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Home / DTC / P1508 — IAC Valve Circuit Failure

P1508 — IAC Valve Circuit Failure

Detailed page for trouble code P1508.

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Code

P1508

ACURA P — Powertrain

IAC Valve Circuit Failure

Brand: ACURA
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
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Code

P1508

BMW P — Powertrain

Idle Speed Control Valve Opening Solenoid Control Open Circuit

Brand: BMW
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
Repair manuals

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Code

P1508

BUICK P — Powertrain

IAC System Low RPM

Brand: BUICK
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
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Code

P1508

CADILLAC P — Powertrain

IAC System Low RPM

Brand: CADILLAC
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
206

Browse 206 CADILLAC manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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Code

P1508

CHEVROLET P — Powertrain

IAC System Low RPM

Brand: CHEVROLET
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
456

Browse 456 CHEVROLET manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

CHEVROLET

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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Code

P1508

CHRYSLER P — Powertrain

IAC System Low RPM

Brand: CHRYSLER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
193

Browse 193 CHRYSLER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

CHRYSLER

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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Code

P1508

DAEWOO P — Powertrain

MPS - SIGNAL LOW

Brand: DAEWOO
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
Repair manuals

Manual library for DAEWOO

75

Browse 75 DAEWOO manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

DAEWOO

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

P1508

GM P — Powertrain

IAC System Low RPM

Brand: GM
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
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Code

P1508

GMC P — Powertrain

IAC System Low RPM

Brand: GMC
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
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Code

P1508

HONDA P — Powertrain

IAC Valve Circuit Failure

Brand: HONDA
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
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Code

P1508

HUMMER P — Powertrain

Idle Speed Low - Idle Air Control (IAC) System Not Responding

Brand: HUMMER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
Repair manuals

Manual library for HUMMER

138

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HUMMER

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Code

P1508

INFINITI P — Powertrain

IAC Valve Circuit Failure

Brand: INFINITI
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
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Send to email
Code

P1508

JAGUAR P — Powertrain

Idle Air Control Circuit Open

Brand: JAGUAR
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
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Code

P1508

KIA P — Powertrain

Idle Air Control Valve Closing Coil Voltage High

Brand: KIA
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
Repair manuals

Manual library for KIA

155

Browse 155 KIA manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

KIA

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Keep it short and practical. Up to 500 characters.
Send to email
Code

P1508

LAND ROVER P — Powertrain

Open circuit of control system of slow motion

Brand: LAND ROVER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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Code

P1508

MAZDA P — Powertrain

Idle Air Control Circuit Open

Brand: MAZDA
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
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Code

P1508

OLDSMOBILE P — Powertrain

IAC System Low RPM

Brand: OLDSMOBILE
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
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Code

P1508

Other P — Powertrain

Idle Control System Circuit Open

Brand: Other
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

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P0505 P0506 P0507 P1506
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Code

P1508

SATURN P — Powertrain

IAC System Low RPM

Brand: SATURN
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

P1508

VOLKSWAGEN P — Powertrain

Idle System Learned Value Upper Limit Attained

Brand: VOLKSWAGEN
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between ECM and IAC valve
  • Corroded, bent or loose connector pins at IAC or ECM
  • Failed IAC valve (stuck, seized, burned coil or failed stepper/motor)
  • Poor or missing ground for IAC circuit
  • Blown fuse or fusible link feeding IAC circuit
  • Carbon/soot build-up restricting IAC movement or throttle body air passages

Symptoms

  • Check Engine Light (MIL) with P1508 stored
  • Unstable idle RPM, surging or hunting at idle
  • Engine stalls when coming to idle or after warm-up
  • High idle or low idle not corrected by throttle
  • Poor idle when accessories (A/C, lights) are switched on
  • Difficulty starting or idle drops immediately after start

What to check

  • Read and record freeze frame and all stored codes with a scan tool; note conditions when code set
  • Visually inspect IAC valve connector, wiring harness, and ECM connector for damage, corrosion, or loose pins
  • Check related fuses and fusible links for continuity
  • Back-probe IAC connector and check for battery voltage and ground with key ON (engine OFF)
  • Measure IAC coil/stepper resistance per manufacturer spec and check for open/short to ground/voltage
  • Use a scan tool to command the IAC (step/position or duty) and observe engine RPM response and stepper counts

Signal parameters

  • Connector supply voltage: ~battery voltage with key ON (expected 11–14 V)
  • Control signal: PWM duty cycle or stepper position/counts (varies by vehicle; expected change when commanding IAC)
  • Resistance: IAC windings/stepper coils should show continuity and be within the manufacturer’s ohms spec (no open circuit or short to ground)
  • Backprobe idle stepper position or duty change when commanding IAC (expect measurable movement or RPM change)

Diagnostic algorithm

  1. Verify code and freeze frame data with a scan tool; clear codes and attempt to re-create.
  2. Perform a visual inspection of IAC valve, throttle body, harness and connectors for damage, corrosion or contamination.
  3. Check fuses and primary ground points; repair any poor ground or blown fuse.
  4. With ignition ON, back-probe the IAC power and control pins: verify battery voltage to the power pin and verify control signal presence while commanding IAC from a scan tool.
  5. Measure resistance of IAC coils/stepper. If open/short, replace IAC.
  6. Command IAC with scan tool (open/close or increase/decrease step count or duty) and observe RPM and step count changes; if no response but wiring and voltage OK, replace IAC.
  7. If IAC responds but code returns, remove and clean throttle body/IAC assembly and retest.
  8. Perform continuity checks from ECM connector to IAC connector to find opens/shorts; repair wiring as needed.
  9. If wiring and IAC are good and proper control signal is absent, test ECM output driver per factory procedures or consider ECM replacement after confirming fault.
  10. After repairs, clear codes and road-test to confirm the fault does not return.

Likely causes

  • Wiring harness damage at harness rub point or near throttle body
  • Corroded connector terminals at IAC valve
  • IAC stepper motor internal failure or worn gears
  • Throttle body carbon preventing valve movement
  • Faulty ground strap or engine ground connection

Fault status

⚠️ Status
IAC Valve Circuit Failure — ECM detected abnormal operation (open/short/intermittent) in the Idle Air Control valve circuit. Inspect wiring, connectors, IAC unit, grounds, fuses and ECM outputs.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0505 P0506 P0507 P1506
626

Browse 626 VOLKSWAGEN manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

VOLKSWAGEN

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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