P0408
EGR Sensor B Circuit High
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
- Record freeze frame, clear codes, and re-run to verify repeatability.
- 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.
- 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.
- Inspect connector and wiring visually; repair any damaged insulation, chafed wiring, or corroded terminals. Wiggle harness while monitoring signal to find intermittent faults.
- 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.
- 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
Similar codes
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P0408
- High Sensor B of the Exhaust Gas Recirculation
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
- Record freeze frame, clear codes, and re-run to verify repeatability.
- 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.
- 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.
- Inspect connector and wiring visually; repair any damaged insulation, chafed wiring, or corroded terminals. Wiggle harness while monitoring signal to find intermittent faults.
- 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.
- 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
Similar codes
P0408
Exhaust Gas Recirculation Sensor B Circuit High
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
- Record freeze frame, clear codes, and re-run to verify repeatability.
- 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.
- 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.
- Inspect connector and wiring visually; repair any damaged insulation, chafed wiring, or corroded terminals. Wiggle harness while monitoring signal to find intermittent faults.
- 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.
- 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
Similar codes
Manual library for HUMMER
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P0408
Sensor exhaust gas recirculation B circuit low
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
- Record freeze frame, clear codes, and re-run to verify repeatability.
- 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.
- 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.
- Inspect connector and wiring visually; repair any damaged insulation, chafed wiring, or corroded terminals. Wiggle harness while monitoring signal to find intermittent faults.
- 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.
- 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
Similar codes
Manual library for LAND ROVER
Browse 274 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
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LAND ROVER: 2023
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Discovery Sport
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Range Rover
- Autobiography, 4.4L Eng VIN 7 · 4.4L Eng VIN 72022: Range Rover Autobiography
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Range Rover Evoque
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Range Rover Velar
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LAND ROVER: 2021
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Discovery Sport
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- SVAutobiography
- SVAutobiography Dynamic
- SVAutobiography Dynamic Blk.
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Range Rover Evoque
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Range Rover Sport
- Autobiography, 2.0L Eng VIN Y · 2.0L Eng VIN Y2021: Range Rover Sport Autobiography
- Autobiography, 5.0L Eng VIN E · 5.0L Eng VIN E2021: Range Rover Sport Autobiography
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- Autobiography Dynamic, 5.0L Eng VIN E · 5.0L Eng VIN E2021: Range Rover Sport Autobiography Dynamic
- HSE Dynamic
- HSE Silver Edition, 2.0L Eng VIN Y · 2.0L Eng VIN Y2021: Range Rover Sport HSE Silver Edition
- HSE Silver Edition, 3.0L Eng VIN K · 3.0L Eng VIN K2021: Range Rover Sport HSE Silver Edition
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Range Rover Velar
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LAND ROVER: 2020
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Defender
- 90 First Edition
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- 110 First Edition
- 110 First Edition
- 110 HSE
- 110 HSE
- 110 S
- 110 S
- 110 SE
- 110 SE
- 110 X
- 110 X
- 110, 2.0L Eng VIN X · 2.0L Eng VIN X2020: Defender 110
- 110, 2.0L Eng VIN X · 2.0L Eng VIN X2020: Defender 110
- 110, 3.0L Eng VIN U · 3.0L Eng VIN U2020: Defender 110
- 110, 3.0L Eng VIN U · 3.0L Eng VIN U2020: Defender 110
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Discovery
- HSE, 3.0L Eng VIN K · 3.0L Eng VIN K2020: Discovery HSE
- HSE, 3.0L Eng VIN K · 3.0L Eng VIN K2020: Discovery HSE
- HSE, 3.0L Eng VIN V · 3.0L Eng VIN V2020: Discovery HSE
- HSE, 3.0L Eng VIN V · 3.0L Eng VIN V2020: Discovery HSE
- HSE Luxury, 3.0L Eng VIN K · 3.0L Eng VIN K2020: Discovery HSE Luxury
- HSE Luxury, 3.0L Eng VIN K · 3.0L Eng VIN K2020: Discovery HSE Luxury
- HSE Luxury, 3.0L Eng VIN V · 3.0L Eng VIN V2020: Discovery HSE Luxury
- HSE Luxury, 3.0L Eng VIN V · 3.0L Eng VIN V2020: Discovery HSE Luxury
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- SE, 3.0L Eng VIN K · 3.0L Eng VIN K2020: Discovery SE
- SE, 3.0L Eng VIN K · 3.0L Eng VIN K2020: Discovery SE
- SE, 3.0L Eng VIN V · 3.0L Eng VIN V2020: Discovery SE
- SE, 3.0L Eng VIN V · 3.0L Eng VIN V2020: Discovery SE
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- Base, 3.0L Eng VIN K · 3.0L Eng VIN K2020: Range Rover Base
- Base, 3.0L Eng VIN K · 3.0L Eng VIN K2020: Range Rover Base
- Base, 3.0L Eng VIN U · 3.0L Eng VIN U2020: Range Rover Base
- Base, 3.0L Eng VIN U · 3.0L Eng VIN U2020: Range Rover Base
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- SVAutobiography
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- SVAutobiography Dynamic
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Range Rover Evoque
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- Autobiography Dynamic, 2.0L Eng VIN Y · 2.0L Eng VIN Y2020: Range Rover Sport Autobiography Dynamic
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Range Rover Velar
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- SVAutobiography Dyn.
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LAND ROVER: 2019
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Discovery
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- HSE Luxury, 3.0L Eng VIN V · 3.0L Eng VIN V2019: Discovery HSE Luxury
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Discovery Sport
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- SVAutobiography
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Range Rover Sport
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- HSE, 3.0L Eng VIN U · 3.0L Eng VIN U2019: Range Rover Sport HSE
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- SE, 3.0L Eng VIN U · 3.0L Eng VIN U2019: Range Rover Sport SE
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Range Rover Velar
- 2019 Range Rover Velar Base
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- R-Dynamic SE, 3.0L Eng VIN V · 3.0L Eng VIN V2019: Range Rover Velar R-Dynamic SE
- R-Dynamic SE, 3.0L Eng VIN V · 3.0L Eng VIN V2019: Range Rover Velar R-Dynamic SE
- S, 2.0L Eng VIN N · 2.0L Eng VIN N2019: Range Rover Velar S
- S, 2.0L Eng VIN X · 2.0L Eng VIN X2019: Range Rover Velar S
- S, 3.0L Eng VIN V · 3.0L Eng VIN V2019: Range Rover Velar S
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