Code
P1550
BMW
P — Powertrain
Idle Speed Control Valve Closing Solenoid Control Circuit Electrical
Views:
UK: 29
EN: 51
RU: 38
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the idle control solenoid circuit
- Corroded, bent, or damaged connector pins at solenoid or ECM
- Failed idle speed control valve closing solenoid (coil open or shorted)
- Faulty ECM/PCM driver output
- Poor ground or supply voltage to the solenoid
- Aftermarket wiring, recent repairs or harness chafing/damage
Symptoms
- Check Engine Light (MIL) illuminated
- Unstable or rough idle
- Idle too high or too low, possible stalling
- Difficulty achieving stable idle after cold start
- Hesitation or surging at low RPM
- Codes return immediately or intermittently
What to check
- Read freeze frame and live data; note when the code set (key on/engine off, cranking, running)
- Visually inspect wiring and connectors for damage, corrosion, or loose pins at solenoid and ECM
- Check related fuses and engine grounds
- Measure supply voltage to solenoid with key ON (should be near battery voltage if solenoid has fused feed)
- Measure solenoid coil resistance with connector disconnected
- Backprobe the control wire while cranking/idle to observe voltage or PWM
Signal parameters
- Supply voltage to solenoid: ~11–14 V (with ignition ON) — verify in service manual
- Solenoid coil resistance: typically low (single to low double-digit ohms). Compare to manufacturer spec before replacing
- Control signal: usually switched to ground or PWM from ECM; duty cycle varies with idle requirements
- Expected control voltage when driven: pulses or switched ground; voltage on control wire may toggle between near 0 V and battery voltage or show PWM waveform on scope
- No continuity to ground or open circuit indicates wiring or solenoid fault; short to battery indicates shorted wiring
Diagnostic algorithm
- Retrieve and record freeze frame and all stored codes; confirm P1550 is current and not historical only.
- Perform a full visual inspection of the idle control valve, solenoid connector, wiring harness, and ECM connector for damage or corrosion.
- With ignition OFF, disconnect solenoid connector and measure coil resistance across the terminals; compare to BMW spec. An open or very high resistance indicates a failed solenoid.
- With connector disconnected, check continuity from solenoid connector pins to the ECM connector pins to confirm no open or high resistance in the harness.
- With ignition ON (engine off) measure supply voltage at the solenoid power pin; verify proper battery voltage. Check ground continuity to chassis.
- Backprobe the control/driver wire with engine running or during cranking to observe behavior. Use a scope if available to confirm PWM frequency and duty cycle; a steady short to ground or battery indicates a fault.
- Wiggle the harness and connectors while monitoring the signal to find intermittent faults caused by movement.
- If wiring and solenoid test good, consult manufacturer service data for ECM driver tests. Replace solenoid only after confirming wiring and supply are good. If ECM driver suspected, perform ECM bench tests or replacement per BMW procedures.
- After repairs, clear codes, perform functional test (cold/hot idle) and road test to confirm the fault does not return.
Likely causes
- Broken or chafed wire between solenoid and ECM
- Failed solenoid coil (open or high resistance)
- Loose/corroded connector terminal at solenoid
- Bad ground at engine harness or battery negative
- ECM driver transistor fault (less common)
Fault status
Status
P1550 — Idle Speed Control Valve Closing Solenoid Control Circuit Electrical: The engine control module detected an electrical problem in the idle speed control valve closing solenoid circuit (open, short, or implausible signal). The fault may cause unstable idle and illumination of the malfunction indicator lamp.
Repair difficulty: Medium
Diagnostic time: 0.5–2.5 hours
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Code
P1550
FORD
P — Powertrain
Power Steering Pressure Sensor Out of Self-Test Range
Views:
UK: 31
EN: 55
RU: 45
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the idle control solenoid circuit
- Corroded, bent, or damaged connector pins at solenoid or ECM
- Failed idle speed control valve closing solenoid (coil open or shorted)
- Faulty ECM/PCM driver output
- Poor ground or supply voltage to the solenoid
- Aftermarket wiring, recent repairs or harness chafing/damage
Symptoms
- Check Engine Light (MIL) illuminated
- Unstable or rough idle
- Idle too high or too low, possible stalling
- Difficulty achieving stable idle after cold start
- Hesitation or surging at low RPM
- Codes return immediately or intermittently
What to check
- Read freeze frame and live data; note when the code set (key on/engine off, cranking, running)
- Visually inspect wiring and connectors for damage, corrosion, or loose pins at solenoid and ECM
- Check related fuses and engine grounds
- Measure supply voltage to solenoid with key ON (should be near battery voltage if solenoid has fused feed)
- Measure solenoid coil resistance with connector disconnected
- Backprobe the control wire while cranking/idle to observe voltage or PWM
Signal parameters
- Supply voltage to solenoid: ~11–14 V (with ignition ON) — verify in service manual
- Solenoid coil resistance: typically low (single to low double-digit ohms). Compare to manufacturer spec before replacing
- Control signal: usually switched to ground or PWM from ECM; duty cycle varies with idle requirements
- Expected control voltage when driven: pulses or switched ground; voltage on control wire may toggle between near 0 V and battery voltage or show PWM waveform on scope
- No continuity to ground or open circuit indicates wiring or solenoid fault; short to battery indicates shorted wiring
Diagnostic algorithm
- Retrieve and record freeze frame and all stored codes; confirm P1550 is current and not historical only.
- Perform a full visual inspection of the idle control valve, solenoid connector, wiring harness, and ECM connector for damage or corrosion.
- With ignition OFF, disconnect solenoid connector and measure coil resistance across the terminals; compare to BMW spec. An open or very high resistance indicates a failed solenoid.
- With connector disconnected, check continuity from solenoid connector pins to the ECM connector pins to confirm no open or high resistance in the harness.
- With ignition ON (engine off) measure supply voltage at the solenoid power pin; verify proper battery voltage. Check ground continuity to chassis.
- Backprobe the control/driver wire with engine running or during cranking to observe behavior. Use a scope if available to confirm PWM frequency and duty cycle; a steady short to ground or battery indicates a fault.
- Wiggle the harness and connectors while monitoring the signal to find intermittent faults caused by movement.
- If wiring and solenoid test good, consult manufacturer service data for ECM driver tests. Replace solenoid only after confirming wiring and supply are good. If ECM driver suspected, perform ECM bench tests or replacement per BMW procedures.
- After repairs, clear codes, perform functional test (cold/hot idle) and road test to confirm the fault does not return.
Likely causes
- Broken or chafed wire between solenoid and ECM
- Failed solenoid coil (open or high resistance)
- Loose/corroded connector terminal at solenoid
- Bad ground at engine harness or battery negative
- ECM driver transistor fault (less common)
Fault status
Status
P1550 — Idle Speed Control Valve Closing Solenoid Control Circuit Electrical: The engine control module detected an electrical problem in the idle speed control valve closing solenoid circuit (open, short, or implausible signal). The fault may cause unstable idle and illumination of the malfunction indicator lamp.
Repair difficulty: Medium
Diagnostic time: 0.5–2.5 hours
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Code
P1550
LINCOLN
P — Powertrain
Power Steering Pressure Sensor Out of Self-Test Range
Views:
UK: 31
EN: 43
RU: 35
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the idle control solenoid circuit
- Corroded, bent, or damaged connector pins at solenoid or ECM
- Failed idle speed control valve closing solenoid (coil open or shorted)
- Faulty ECM/PCM driver output
- Poor ground or supply voltage to the solenoid
- Aftermarket wiring, recent repairs or harness chafing/damage
Symptoms
- Check Engine Light (MIL) illuminated
- Unstable or rough idle
- Idle too high or too low, possible stalling
- Difficulty achieving stable idle after cold start
- Hesitation or surging at low RPM
- Codes return immediately or intermittently
What to check
- Read freeze frame and live data; note when the code set (key on/engine off, cranking, running)
- Visually inspect wiring and connectors for damage, corrosion, or loose pins at solenoid and ECM
- Check related fuses and engine grounds
- Measure supply voltage to solenoid with key ON (should be near battery voltage if solenoid has fused feed)
- Measure solenoid coil resistance with connector disconnected
- Backprobe the control wire while cranking/idle to observe voltage or PWM
Signal parameters
- Supply voltage to solenoid: ~11–14 V (with ignition ON) — verify in service manual
- Solenoid coil resistance: typically low (single to low double-digit ohms). Compare to manufacturer spec before replacing
- Control signal: usually switched to ground or PWM from ECM; duty cycle varies with idle requirements
- Expected control voltage when driven: pulses or switched ground; voltage on control wire may toggle between near 0 V and battery voltage or show PWM waveform on scope
- No continuity to ground or open circuit indicates wiring or solenoid fault; short to battery indicates shorted wiring
Diagnostic algorithm
- Retrieve and record freeze frame and all stored codes; confirm P1550 is current and not historical only.
- Perform a full visual inspection of the idle control valve, solenoid connector, wiring harness, and ECM connector for damage or corrosion.
- With ignition OFF, disconnect solenoid connector and measure coil resistance across the terminals; compare to BMW spec. An open or very high resistance indicates a failed solenoid.
- With connector disconnected, check continuity from solenoid connector pins to the ECM connector pins to confirm no open or high resistance in the harness.
- With ignition ON (engine off) measure supply voltage at the solenoid power pin; verify proper battery voltage. Check ground continuity to chassis.
- Backprobe the control/driver wire with engine running or during cranking to observe behavior. Use a scope if available to confirm PWM frequency and duty cycle; a steady short to ground or battery indicates a fault.
- Wiggle the harness and connectors while monitoring the signal to find intermittent faults caused by movement.
- If wiring and solenoid test good, consult manufacturer service data for ECM driver tests. Replace solenoid only after confirming wiring and supply are good. If ECM driver suspected, perform ECM bench tests or replacement per BMW procedures.
- After repairs, clear codes, perform functional test (cold/hot idle) and road test to confirm the fault does not return.
Likely causes
- Broken or chafed wire between solenoid and ECM
- Failed solenoid coil (open or high resistance)
- Loose/corroded connector terminal at solenoid
- Bad ground at engine harness or battery negative
- ECM driver transistor fault (less common)
Fault status
Status
P1550 — Idle Speed Control Valve Closing Solenoid Control Circuit Electrical: The engine control module detected an electrical problem in the idle speed control valve closing solenoid circuit (open, short, or implausible signal). The fault may cause unstable idle and illumination of the malfunction indicator lamp.
Repair difficulty: Medium
Diagnostic time: 0.5–2.5 hours
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Code
P1550
MERCURY
P — Powertrain
Power Steering Pressure Sensor Out of Self-Test Range
Views:
UK: 29
EN: 44
RU: 42
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the idle control solenoid circuit
- Corroded, bent, or damaged connector pins at solenoid or ECM
- Failed idle speed control valve closing solenoid (coil open or shorted)
- Faulty ECM/PCM driver output
- Poor ground or supply voltage to the solenoid
- Aftermarket wiring, recent repairs or harness chafing/damage
Symptoms
- Check Engine Light (MIL) illuminated
- Unstable or rough idle
- Idle too high or too low, possible stalling
- Difficulty achieving stable idle after cold start
- Hesitation or surging at low RPM
- Codes return immediately or intermittently
What to check
- Read freeze frame and live data; note when the code set (key on/engine off, cranking, running)
- Visually inspect wiring and connectors for damage, corrosion, or loose pins at solenoid and ECM
- Check related fuses and engine grounds
- Measure supply voltage to solenoid with key ON (should be near battery voltage if solenoid has fused feed)
- Measure solenoid coil resistance with connector disconnected
- Backprobe the control wire while cranking/idle to observe voltage or PWM
Signal parameters
- Supply voltage to solenoid: ~11–14 V (with ignition ON) — verify in service manual
- Solenoid coil resistance: typically low (single to low double-digit ohms). Compare to manufacturer spec before replacing
- Control signal: usually switched to ground or PWM from ECM; duty cycle varies with idle requirements
- Expected control voltage when driven: pulses or switched ground; voltage on control wire may toggle between near 0 V and battery voltage or show PWM waveform on scope
- No continuity to ground or open circuit indicates wiring or solenoid fault; short to battery indicates shorted wiring
Diagnostic algorithm
- Retrieve and record freeze frame and all stored codes; confirm P1550 is current and not historical only.
- Perform a full visual inspection of the idle control valve, solenoid connector, wiring harness, and ECM connector for damage or corrosion.
- With ignition OFF, disconnect solenoid connector and measure coil resistance across the terminals; compare to BMW spec. An open or very high resistance indicates a failed solenoid.
- With connector disconnected, check continuity from solenoid connector pins to the ECM connector pins to confirm no open or high resistance in the harness.
- With ignition ON (engine off) measure supply voltage at the solenoid power pin; verify proper battery voltage. Check ground continuity to chassis.
- Backprobe the control/driver wire with engine running or during cranking to observe behavior. Use a scope if available to confirm PWM frequency and duty cycle; a steady short to ground or battery indicates a fault.
- Wiggle the harness and connectors while monitoring the signal to find intermittent faults caused by movement.
- If wiring and solenoid test good, consult manufacturer service data for ECM driver tests. Replace solenoid only after confirming wiring and supply are good. If ECM driver suspected, perform ECM bench tests or replacement per BMW procedures.
- After repairs, clear codes, perform functional test (cold/hot idle) and road test to confirm the fault does not return.
Likely causes
- Broken or chafed wire between solenoid and ECM
- Failed solenoid coil (open or high resistance)
- Loose/corroded connector terminal at solenoid
- Bad ground at engine harness or battery negative
- ECM driver transistor fault (less common)
Fault status
Status
P1550 — Idle Speed Control Valve Closing Solenoid Control Circuit Electrical: The engine control module detected an electrical problem in the idle speed control valve closing solenoid circuit (open, short, or implausible signal). The fault may cause unstable idle and illumination of the malfunction indicator lamp.
Repair difficulty: Medium
Diagnostic time: 0.5–2.5 hours
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Code
P1550
NISSAN
P — Powertrain
TCC Solenoid Valve
Views:
UK: 32
EN: 72
RU: 43
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the idle control solenoid circuit
- Corroded, bent, or damaged connector pins at solenoid or ECM
- Failed idle speed control valve closing solenoid (coil open or shorted)
- Faulty ECM/PCM driver output
- Poor ground or supply voltage to the solenoid
- Aftermarket wiring, recent repairs or harness chafing/damage
Symptoms
- Check Engine Light (MIL) illuminated
- Unstable or rough idle
- Idle too high or too low, possible stalling
- Difficulty achieving stable idle after cold start
- Hesitation or surging at low RPM
- Codes return immediately or intermittently
What to check
- Read freeze frame and live data; note when the code set (key on/engine off, cranking, running)
- Visually inspect wiring and connectors for damage, corrosion, or loose pins at solenoid and ECM
- Check related fuses and engine grounds
- Measure supply voltage to solenoid with key ON (should be near battery voltage if solenoid has fused feed)
- Measure solenoid coil resistance with connector disconnected
- Backprobe the control wire while cranking/idle to observe voltage or PWM
Signal parameters
- Supply voltage to solenoid: ~11–14 V (with ignition ON) — verify in service manual
- Solenoid coil resistance: typically low (single to low double-digit ohms). Compare to manufacturer spec before replacing
- Control signal: usually switched to ground or PWM from ECM; duty cycle varies with idle requirements
- Expected control voltage when driven: pulses or switched ground; voltage on control wire may toggle between near 0 V and battery voltage or show PWM waveform on scope
- No continuity to ground or open circuit indicates wiring or solenoid fault; short to battery indicates shorted wiring
Diagnostic algorithm
- Retrieve and record freeze frame and all stored codes; confirm P1550 is current and not historical only.
- Perform a full visual inspection of the idle control valve, solenoid connector, wiring harness, and ECM connector for damage or corrosion.
- With ignition OFF, disconnect solenoid connector and measure coil resistance across the terminals; compare to BMW spec. An open or very high resistance indicates a failed solenoid.
- With connector disconnected, check continuity from solenoid connector pins to the ECM connector pins to confirm no open or high resistance in the harness.
- With ignition ON (engine off) measure supply voltage at the solenoid power pin; verify proper battery voltage. Check ground continuity to chassis.
- Backprobe the control/driver wire with engine running or during cranking to observe behavior. Use a scope if available to confirm PWM frequency and duty cycle; a steady short to ground or battery indicates a fault.
- Wiggle the harness and connectors while monitoring the signal to find intermittent faults caused by movement.
- If wiring and solenoid test good, consult manufacturer service data for ECM driver tests. Replace solenoid only after confirming wiring and supply are good. If ECM driver suspected, perform ECM bench tests or replacement per BMW procedures.
- After repairs, clear codes, perform functional test (cold/hot idle) and road test to confirm the fault does not return.
Likely causes
- Broken or chafed wire between solenoid and ECM
- Failed solenoid coil (open or high resistance)
- Loose/corroded connector terminal at solenoid
- Bad ground at engine harness or battery negative
- ECM driver transistor fault (less common)
Fault status
Status
P1550 — Idle Speed Control Valve Closing Solenoid Control Circuit Electrical: The engine control module detected an electrical problem in the idle speed control valve closing solenoid circuit (open, short, or implausible signal). The fault may cause unstable idle and illumination of the malfunction indicator lamp.
Repair difficulty: Medium
Diagnostic time: 0.5–2.5 hours
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Code
P1550
Other
P — Powertrain
PSPS Out Of Self Test Range
Views:
UK: 32
EN: 43
RU: 38
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the idle control solenoid circuit
- Corroded, bent, or damaged connector pins at solenoid or ECM
- Failed idle speed control valve closing solenoid (coil open or shorted)
- Faulty ECM/PCM driver output
- Poor ground or supply voltage to the solenoid
- Aftermarket wiring, recent repairs or harness chafing/damage
Symptoms
- Check Engine Light (MIL) illuminated
- Unstable or rough idle
- Idle too high or too low, possible stalling
- Difficulty achieving stable idle after cold start
- Hesitation or surging at low RPM
- Codes return immediately or intermittently
What to check
- Read freeze frame and live data; note when the code set (key on/engine off, cranking, running)
- Visually inspect wiring and connectors for damage, corrosion, or loose pins at solenoid and ECM
- Check related fuses and engine grounds
- Measure supply voltage to solenoid with key ON (should be near battery voltage if solenoid has fused feed)
- Measure solenoid coil resistance with connector disconnected
- Backprobe the control wire while cranking/idle to observe voltage or PWM
Signal parameters
- Supply voltage to solenoid: ~11–14 V (with ignition ON) — verify in service manual
- Solenoid coil resistance: typically low (single to low double-digit ohms). Compare to manufacturer spec before replacing
- Control signal: usually switched to ground or PWM from ECM; duty cycle varies with idle requirements
- Expected control voltage when driven: pulses or switched ground; voltage on control wire may toggle between near 0 V and battery voltage or show PWM waveform on scope
- No continuity to ground or open circuit indicates wiring or solenoid fault; short to battery indicates shorted wiring
Diagnostic algorithm
- Retrieve and record freeze frame and all stored codes; confirm P1550 is current and not historical only.
- Perform a full visual inspection of the idle control valve, solenoid connector, wiring harness, and ECM connector for damage or corrosion.
- With ignition OFF, disconnect solenoid connector and measure coil resistance across the terminals; compare to BMW spec. An open or very high resistance indicates a failed solenoid.
- With connector disconnected, check continuity from solenoid connector pins to the ECM connector pins to confirm no open or high resistance in the harness.
- With ignition ON (engine off) measure supply voltage at the solenoid power pin; verify proper battery voltage. Check ground continuity to chassis.
- Backprobe the control/driver wire with engine running or during cranking to observe behavior. Use a scope if available to confirm PWM frequency and duty cycle; a steady short to ground or battery indicates a fault.
- Wiggle the harness and connectors while monitoring the signal to find intermittent faults caused by movement.
- If wiring and solenoid test good, consult manufacturer service data for ECM driver tests. Replace solenoid only after confirming wiring and supply are good. If ECM driver suspected, perform ECM bench tests or replacement per BMW procedures.
- After repairs, clear codes, perform functional test (cold/hot idle) and road test to confirm the fault does not return.
Likely causes
- Broken or chafed wire between solenoid and ECM
- Failed solenoid coil (open or high resistance)
- Loose/corroded connector terminal at solenoid
- Bad ground at engine harness or battery negative
- ECM driver transistor fault (less common)
Fault status
Status
P1550 — Idle Speed Control Valve Closing Solenoid Control Circuit Electrical: The engine control module detected an electrical problem in the idle speed control valve closing solenoid circuit (open, short, or implausible signal). The fault may cause unstable idle and illumination of the malfunction indicator lamp.
Repair difficulty: Medium
Diagnostic time: 0.5–2.5 hours
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Code
P1550
SCION
P — Powertrain
Power steering pressure sensor circuit malfunction
Views:
UK: 13
EN: 17
RU: 14
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the idle control solenoid circuit
- Corroded, bent, or damaged connector pins at solenoid or ECM
- Failed idle speed control valve closing solenoid (coil open or shorted)
- Faulty ECM/PCM driver output
- Poor ground or supply voltage to the solenoid
- Aftermarket wiring, recent repairs or harness chafing/damage
Symptoms
- Check Engine Light (MIL) illuminated
- Unstable or rough idle
- Idle too high or too low, possible stalling
- Difficulty achieving stable idle after cold start
- Hesitation or surging at low RPM
- Codes return immediately or intermittently
What to check
- Read freeze frame and live data; note when the code set (key on/engine off, cranking, running)
- Visually inspect wiring and connectors for damage, corrosion, or loose pins at solenoid and ECM
- Check related fuses and engine grounds
- Measure supply voltage to solenoid with key ON (should be near battery voltage if solenoid has fused feed)
- Measure solenoid coil resistance with connector disconnected
- Backprobe the control wire while cranking/idle to observe voltage or PWM
Signal parameters
- Supply voltage to solenoid: ~11–14 V (with ignition ON) — verify in service manual
- Solenoid coil resistance: typically low (single to low double-digit ohms). Compare to manufacturer spec before replacing
- Control signal: usually switched to ground or PWM from ECM; duty cycle varies with idle requirements
- Expected control voltage when driven: pulses or switched ground; voltage on control wire may toggle between near 0 V and battery voltage or show PWM waveform on scope
- No continuity to ground or open circuit indicates wiring or solenoid fault; short to battery indicates shorted wiring
Diagnostic algorithm
- Retrieve and record freeze frame and all stored codes; confirm P1550 is current and not historical only.
- Perform a full visual inspection of the idle control valve, solenoid connector, wiring harness, and ECM connector for damage or corrosion.
- With ignition OFF, disconnect solenoid connector and measure coil resistance across the terminals; compare to BMW spec. An open or very high resistance indicates a failed solenoid.
- With connector disconnected, check continuity from solenoid connector pins to the ECM connector pins to confirm no open or high resistance in the harness.
- With ignition ON (engine off) measure supply voltage at the solenoid power pin; verify proper battery voltage. Check ground continuity to chassis.
- Backprobe the control/driver wire with engine running or during cranking to observe behavior. Use a scope if available to confirm PWM frequency and duty cycle; a steady short to ground or battery indicates a fault.
- Wiggle the harness and connectors while monitoring the signal to find intermittent faults caused by movement.
- If wiring and solenoid test good, consult manufacturer service data for ECM driver tests. Replace solenoid only after confirming wiring and supply are good. If ECM driver suspected, perform ECM bench tests or replacement per BMW procedures.
- After repairs, clear codes, perform functional test (cold/hot idle) and road test to confirm the fault does not return.
Likely causes
- Broken or chafed wire between solenoid and ECM
- Failed solenoid coil (open or high resistance)
- Loose/corroded connector terminal at solenoid
- Bad ground at engine harness or battery negative
- ECM driver transistor fault (less common)
Fault status
Status
P1550 — Idle Speed Control Valve Closing Solenoid Control Circuit Electrical: The engine control module detected an electrical problem in the idle speed control valve closing solenoid circuit (open, short, or implausible signal). The fault may cause unstable idle and illumination of the malfunction indicator lamp.
Repair difficulty: Medium
Diagnostic time: 0.5–2.5 hours
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Code
P1550
VOLKSWAGEN
P — Powertrain
Charge Pressure Deviation
Views:
UK: 28
EN: 41
RU: 40
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the idle control solenoid circuit
- Corroded, bent, or damaged connector pins at solenoid or ECM
- Failed idle speed control valve closing solenoid (coil open or shorted)
- Faulty ECM/PCM driver output
- Poor ground or supply voltage to the solenoid
- Aftermarket wiring, recent repairs or harness chafing/damage
Symptoms
- Check Engine Light (MIL) illuminated
- Unstable or rough idle
- Idle too high or too low, possible stalling
- Difficulty achieving stable idle after cold start
- Hesitation or surging at low RPM
- Codes return immediately or intermittently
What to check
- Read freeze frame and live data; note when the code set (key on/engine off, cranking, running)
- Visually inspect wiring and connectors for damage, corrosion, or loose pins at solenoid and ECM
- Check related fuses and engine grounds
- Measure supply voltage to solenoid with key ON (should be near battery voltage if solenoid has fused feed)
- Measure solenoid coil resistance with connector disconnected
- Backprobe the control wire while cranking/idle to observe voltage or PWM
Signal parameters
- Supply voltage to solenoid: ~11–14 V (with ignition ON) — verify in service manual
- Solenoid coil resistance: typically low (single to low double-digit ohms). Compare to manufacturer spec before replacing
- Control signal: usually switched to ground or PWM from ECM; duty cycle varies with idle requirements
- Expected control voltage when driven: pulses or switched ground; voltage on control wire may toggle between near 0 V and battery voltage or show PWM waveform on scope
- No continuity to ground or open circuit indicates wiring or solenoid fault; short to battery indicates shorted wiring
Diagnostic algorithm
- Retrieve and record freeze frame and all stored codes; confirm P1550 is current and not historical only.
- Perform a full visual inspection of the idle control valve, solenoid connector, wiring harness, and ECM connector for damage or corrosion.
- With ignition OFF, disconnect solenoid connector and measure coil resistance across the terminals; compare to BMW spec. An open or very high resistance indicates a failed solenoid.
- With connector disconnected, check continuity from solenoid connector pins to the ECM connector pins to confirm no open or high resistance in the harness.
- With ignition ON (engine off) measure supply voltage at the solenoid power pin; verify proper battery voltage. Check ground continuity to chassis.
- Backprobe the control/driver wire with engine running or during cranking to observe behavior. Use a scope if available to confirm PWM frequency and duty cycle; a steady short to ground or battery indicates a fault.
- Wiggle the harness and connectors while monitoring the signal to find intermittent faults caused by movement.
- If wiring and solenoid test good, consult manufacturer service data for ECM driver tests. Replace solenoid only after confirming wiring and supply are good. If ECM driver suspected, perform ECM bench tests or replacement per BMW procedures.
- After repairs, clear codes, perform functional test (cold/hot idle) and road test to confirm the fault does not return.
Likely causes
- Broken or chafed wire between solenoid and ECM
- Failed solenoid coil (open or high resistance)
- Loose/corroded connector terminal at solenoid
- Bad ground at engine harness or battery negative
- ECM driver transistor fault (less common)
Fault status
Status
P1550 — Idle Speed Control Valve Closing Solenoid Control Circuit Electrical: The engine control module detected an electrical problem in the idle speed control valve closing solenoid circuit (open, short, or implausible signal). The fault may cause unstable idle and illumination of the malfunction indicator lamp.
Repair difficulty: Medium
Diagnostic time: 0.5–2.5 hours
Similar codes
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