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Home / DTC / P0408 — EGR Sensor B Circuit High

P0408 — EGR Sensor B Circuit High

Detailed page for trouble code P0408.

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Code

P0408

Generic P — Powertrain

EGR Sensor B Circuit High

Brand: Generic
Type: P — Powertrain
Views: UK: 17 EN: 26 RU: 13
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or damaged EGR sensor harness insulation with intermittent contact
  • Short to battery or to the 5V reference supply on the EGR Sensor B signal wire
  • Failed EGR position/feedback sensor (internal short or internal electronics fault)
  • Poor or corroded connector or terminal at sensor or PCM
  • Bad sensor ground or reference supply at PCM
  • PCM input circuit fault (rare)

Symptoms

  • Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
  • Possible rough idle, hesitation, or stalling under certain conditions
  • Reduced drivability or torque during some load conditions
  • Failed emissions test due to improper EGR operation
  • In some cases no noticeable driveability symptoms aside from MIL

What to check

  • Retrieve freeze frame and all stored codes; note engine conditions when code set
  • Monitor live EGR sensor B data with a scan tool (voltage or position) at key‑on and while running
  • Backprobe the sensor connector: measure signal, reference (usually +5V), and ground
  • Inspect sensor connector and wiring harness for damage, corrosion, pin push‑outs, chafing, or repairs
  • Wiggle harness and connector while monitoring signal for intermittent changes
  • Compare measured signal to expected parameters (see signal_params)

Signal parameters

  • Typical EGR position/feedback sensor output (generic): about 0.5 V when closed, rising up to ~4.5 V when open (varies by manufacturer)
  • Reference supply: stable +5.0 V (approx) at sensor reference pin with key ON
  • Ground: near 0.0 V at sensor ground pin
  • Circuit-high event threshold (generic): sensor signal higher than ~4.7–4.9 V, or sudden jump to battery voltage — triggers P0408 on many systems
  • Note: actual values and circuits vary by manufacturer. Always confirm vehicle-specific specs.

Diagnostic algorithm

  1. Record freeze frame, clear codes, and re-run to verify repeatability.
  2. With key ON (engine OFF) backprobe sensor connector: verify 5V reference present and stable, verify ground continuity to chassis/PCM, measure signal voltage. A signal at or near battery voltage or a constant >4.7V indicates a circuit-high condition.
  3. With engine running, monitor live EGR sensor B output. Observe behavior during idle and commanded EGR events (if tool can actuate EGR). Look for stuck-high or implausible values.
  4. Inspect connector and wiring visually; repair any damaged insulation, chafed wiring, or corroded terminals. Wiggle harness while monitoring signal to find intermittent faults.
  5. If signal stays high with sensor disconnected (voltage present at harness), suspect a short to 5V or battery on the harness or PCM output stuck. Measure continuity between signal wire and 5V/battery circuits.
  6. Measure resistance/continuity from sensor signal and ground pins to the PCM to confirm there are no opens, shorts, or low resistance to supply.

Likely causes

  • Shorted signal wire to vehicle 5V reference or battery (most likely when voltage reads above expected)
  • Failed EGR position/feedback sensor (common)
  • Connector corrosion or poor pin connection at the sensor or PCM
  • Bad ground or intermittent power/reference feed to the sensor

Fault status

⚠️ Status
PCM detected EGR Sensor B signal higher than allowed (circuit high). Possible causes: short to 5V/battery, failed sensor, wiring/connector fault, or less commonly PCM input failure. Verify sensor power/ground, inspect wiring and connector, and test/replace sensor as required.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0406 P0407 P0409 P0401 P0402 P0403
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Code

P0408

GWM P — Powertrain

- High Sensor B of the Exhaust Gas Recirculation

Brand: GWM
Type: P — Powertrain
Views: UK: 6 EN: 10 RU: 2
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or damaged EGR sensor harness insulation with intermittent contact
  • Short to battery or to the 5V reference supply on the EGR Sensor B signal wire
  • Failed EGR position/feedback sensor (internal short or internal electronics fault)
  • Poor or corroded connector or terminal at sensor or PCM
  • Bad sensor ground or reference supply at PCM
  • PCM input circuit fault (rare)

Symptoms

  • Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
  • Possible rough idle, hesitation, or stalling under certain conditions
  • Reduced drivability or torque during some load conditions
  • Failed emissions test due to improper EGR operation
  • In some cases no noticeable driveability symptoms aside from MIL

What to check

  • Retrieve freeze frame and all stored codes; note engine conditions when code set
  • Monitor live EGR sensor B data with a scan tool (voltage or position) at key‑on and while running
  • Backprobe the sensor connector: measure signal, reference (usually +5V), and ground
  • Inspect sensor connector and wiring harness for damage, corrosion, pin push‑outs, chafing, or repairs
  • Wiggle harness and connector while monitoring signal for intermittent changes
  • Compare measured signal to expected parameters (see signal_params)

Signal parameters

  • Typical EGR position/feedback sensor output (generic): about 0.5 V when closed, rising up to ~4.5 V when open (varies by manufacturer)
  • Reference supply: stable +5.0 V (approx) at sensor reference pin with key ON
  • Ground: near 0.0 V at sensor ground pin
  • Circuit-high event threshold (generic): sensor signal higher than ~4.7–4.9 V, or sudden jump to battery voltage — triggers P0408 on many systems
  • Note: actual values and circuits vary by manufacturer. Always confirm vehicle-specific specs.

Diagnostic algorithm

  1. Record freeze frame, clear codes, and re-run to verify repeatability.
  2. With key ON (engine OFF) backprobe sensor connector: verify 5V reference present and stable, verify ground continuity to chassis/PCM, measure signal voltage. A signal at or near battery voltage or a constant >4.7V indicates a circuit-high condition.
  3. With engine running, monitor live EGR sensor B output. Observe behavior during idle and commanded EGR events (if tool can actuate EGR). Look for stuck-high or implausible values.
  4. Inspect connector and wiring visually; repair any damaged insulation, chafed wiring, or corroded terminals. Wiggle harness while monitoring signal to find intermittent faults.
  5. If signal stays high with sensor disconnected (voltage present at harness), suspect a short to 5V or battery on the harness or PCM output stuck. Measure continuity between signal wire and 5V/battery circuits.
  6. Measure resistance/continuity from sensor signal and ground pins to the PCM to confirm there are no opens, shorts, or low resistance to supply.

Likely causes

  • Shorted signal wire to vehicle 5V reference or battery (most likely when voltage reads above expected)
  • Failed EGR position/feedback sensor (common)
  • Connector corrosion or poor pin connection at the sensor or PCM
  • Bad ground or intermittent power/reference feed to the sensor

Fault status

⚠️ Status
PCM detected EGR Sensor B signal higher than allowed (circuit high). Possible causes: short to 5V/battery, failed sensor, wiring/connector fault, or less commonly PCM input failure. Verify sensor power/ground, inspect wiring and connector, and test/replace sensor as required.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0406 P0407 P0409 P0401 P0402 P0403
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

P0408

HUMMER P — Powertrain

Exhaust Gas Recirculation Sensor B Circuit High

Brand: HUMMER
Type: P — Powertrain
Views: UK: 14 EN: 19 RU: 10
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or damaged EGR sensor harness insulation with intermittent contact
  • Short to battery or to the 5V reference supply on the EGR Sensor B signal wire
  • Failed EGR position/feedback sensor (internal short or internal electronics fault)
  • Poor or corroded connector or terminal at sensor or PCM
  • Bad sensor ground or reference supply at PCM
  • PCM input circuit fault (rare)

Symptoms

  • Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
  • Possible rough idle, hesitation, or stalling under certain conditions
  • Reduced drivability or torque during some load conditions
  • Failed emissions test due to improper EGR operation
  • In some cases no noticeable driveability symptoms aside from MIL

What to check

  • Retrieve freeze frame and all stored codes; note engine conditions when code set
  • Monitor live EGR sensor B data with a scan tool (voltage or position) at key‑on and while running
  • Backprobe the sensor connector: measure signal, reference (usually +5V), and ground
  • Inspect sensor connector and wiring harness for damage, corrosion, pin push‑outs, chafing, or repairs
  • Wiggle harness and connector while monitoring signal for intermittent changes
  • Compare measured signal to expected parameters (see signal_params)

Signal parameters

  • Typical EGR position/feedback sensor output (generic): about 0.5 V when closed, rising up to ~4.5 V when open (varies by manufacturer)
  • Reference supply: stable +5.0 V (approx) at sensor reference pin with key ON
  • Ground: near 0.0 V at sensor ground pin
  • Circuit-high event threshold (generic): sensor signal higher than ~4.7–4.9 V, or sudden jump to battery voltage — triggers P0408 on many systems
  • Note: actual values and circuits vary by manufacturer. Always confirm vehicle-specific specs.

Diagnostic algorithm

  1. Record freeze frame, clear codes, and re-run to verify repeatability.
  2. With key ON (engine OFF) backprobe sensor connector: verify 5V reference present and stable, verify ground continuity to chassis/PCM, measure signal voltage. A signal at or near battery voltage or a constant >4.7V indicates a circuit-high condition.
  3. With engine running, monitor live EGR sensor B output. Observe behavior during idle and commanded EGR events (if tool can actuate EGR). Look for stuck-high or implausible values.
  4. Inspect connector and wiring visually; repair any damaged insulation, chafed wiring, or corroded terminals. Wiggle harness while monitoring signal to find intermittent faults.
  5. If signal stays high with sensor disconnected (voltage present at harness), suspect a short to 5V or battery on the harness or PCM output stuck. Measure continuity between signal wire and 5V/battery circuits.
  6. Measure resistance/continuity from sensor signal and ground pins to the PCM to confirm there are no opens, shorts, or low resistance to supply.

Likely causes

  • Shorted signal wire to vehicle 5V reference or battery (most likely when voltage reads above expected)
  • Failed EGR position/feedback sensor (common)
  • Connector corrosion or poor pin connection at the sensor or PCM
  • Bad ground or intermittent power/reference feed to the sensor

Fault status

⚠️ Status
PCM detected EGR Sensor B signal higher than allowed (circuit high). Possible causes: short to 5V/battery, failed sensor, wiring/connector fault, or less commonly PCM input failure. Verify sensor power/ground, inspect wiring and connector, and test/replace sensor as required.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0406 P0407 P0409 P0401 P0402 P0403
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

P0408

LAND ROVER P — Powertrain

Sensor exhaust gas recirculation B circuit low

Brand: LAND ROVER
Type: P — Powertrain
Views: UK: 10 EN: 15 RU: 7
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or damaged EGR sensor harness insulation with intermittent contact
  • Short to battery or to the 5V reference supply on the EGR Sensor B signal wire
  • Failed EGR position/feedback sensor (internal short or internal electronics fault)
  • Poor or corroded connector or terminal at sensor or PCM
  • Bad sensor ground or reference supply at PCM
  • PCM input circuit fault (rare)

Symptoms

  • Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
  • Possible rough idle, hesitation, or stalling under certain conditions
  • Reduced drivability or torque during some load conditions
  • Failed emissions test due to improper EGR operation
  • In some cases no noticeable driveability symptoms aside from MIL

What to check

  • Retrieve freeze frame and all stored codes; note engine conditions when code set
  • Monitor live EGR sensor B data with a scan tool (voltage or position) at key‑on and while running
  • Backprobe the sensor connector: measure signal, reference (usually +5V), and ground
  • Inspect sensor connector and wiring harness for damage, corrosion, pin push‑outs, chafing, or repairs
  • Wiggle harness and connector while monitoring signal for intermittent changes
  • Compare measured signal to expected parameters (see signal_params)

Signal parameters

  • Typical EGR position/feedback sensor output (generic): about 0.5 V when closed, rising up to ~4.5 V when open (varies by manufacturer)
  • Reference supply: stable +5.0 V (approx) at sensor reference pin with key ON
  • Ground: near 0.0 V at sensor ground pin
  • Circuit-high event threshold (generic): sensor signal higher than ~4.7–4.9 V, or sudden jump to battery voltage — triggers P0408 on many systems
  • Note: actual values and circuits vary by manufacturer. Always confirm vehicle-specific specs.

Diagnostic algorithm

  1. Record freeze frame, clear codes, and re-run to verify repeatability.
  2. With key ON (engine OFF) backprobe sensor connector: verify 5V reference present and stable, verify ground continuity to chassis/PCM, measure signal voltage. A signal at or near battery voltage or a constant >4.7V indicates a circuit-high condition.
  3. With engine running, monitor live EGR sensor B output. Observe behavior during idle and commanded EGR events (if tool can actuate EGR). Look for stuck-high or implausible values.
  4. Inspect connector and wiring visually; repair any damaged insulation, chafed wiring, or corroded terminals. Wiggle harness while monitoring signal to find intermittent faults.
  5. If signal stays high with sensor disconnected (voltage present at harness), suspect a short to 5V or battery on the harness or PCM output stuck. Measure continuity between signal wire and 5V/battery circuits.
  6. Measure resistance/continuity from sensor signal and ground pins to the PCM to confirm there are no opens, shorts, or low resistance to supply.

Likely causes

  • Shorted signal wire to vehicle 5V reference or battery (most likely when voltage reads above expected)
  • Failed EGR position/feedback sensor (common)
  • Connector corrosion or poor pin connection at the sensor or PCM
  • Bad ground or intermittent power/reference feed to the sensor

Fault status

⚠️ Status
PCM detected EGR Sensor B signal higher than allowed (circuit high). Possible causes: short to 5V/battery, failed sensor, wiring/connector fault, or less commonly PCM input failure. Verify sensor power/ground, inspect wiring and connector, and test/replace sensor as required.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0406 P0407 P0409 P0401 P0402 P0403
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3

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Defender 300Tdi Years: 1996 Manual in English 7.5 MB
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Land Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)

Workshop Manual
Manual in English Pages: 494 7.1 MB
Short description

Land Rover Range Rover Electrical Library (LRL 0453ENG). Comprehensive manual covering fuse details, earth points, system descriptions, diagnostics and connector pin-outs for electrical troubleshooting and repair. Intended for technicians and service workshops.

199,00 UAH
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Key sections:
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