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Home / DTC / P0401 — Restriction in the EGR passages usually caused by carbon buildup, The EGR Valve is defective, Lack of proper vacuum or electrical signal to the EGR valve, Malfunctioning EGR Vacuum supply solenoid, Lack of proper EGR system feedback to the computer from the: Manifold Absolute Pressure Sensor (MAP), Differential EGR Pressure Feedback Sensor (DPFE), EGR Valve Position Sensor (EVP), EGR Temperature Sensor

P0401 — Restriction in the EGR passages usually caused by carbon buildup, The EGR Valve is defective, Lack of proper vacuum or electrical signal to the EGR valve, Malfunctioning EGR Vacuum supply solenoid, Lack of proper EGR system feedback to the computer from the: Manifold Absolute Pressure Sensor (MAP), Differential EGR Pressure Feedback Sensor (DPFE), EGR Valve Position Sensor (EVP), EGR Temperature Sensor

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P0401

AUDI P — Powertrain

Restriction in the EGR passages usually caused by carbon buildup, The EGR Valve is defective, Lack of proper vacuum or electrical signal to the EGR valve, Malfunctioning EGR Vacuum supply solenoid, Lack of proper EGR system feedback to the computer from the: Manifold Absolute Pressure Sensor (MAP), Differential EGR Pressure Feedback Sensor (DPFE), EGR Valve Position Sensor (EVP), EGR Temperature Sensor

Brand: AUDI
Type: P — Powertrain
Views: UK: 45 EN: 67 RU: 130
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Carbon buildup/clogged EGR passages or EGR cooler
  • EGR valve stuck closed or mechanically seized
  • Failed EGR valve (electrical or vacuum-actuated)
  • Faulty EGR vacuum supply solenoid or hose leaks (vacuum systems)
  • Loss of electrical drive to EGR actuator (wiring, connector, fuse)
  • Defective or incorrect feedback from MAP, DPFE (differential pressure), EGR valve position sensor, or EGR temperature sensor

Symptoms

  • Check Engine Light (MIL) illuminated; code P0401 stored
  • Poor idle, hesitation or stumble under light load
  • Slight roughness or increased NOx emissions
  • Possible reduced fuel economy or increased combustion knock under some conditions
  • Engine may run normally at wide-open-throttle (EGR usually disabled at WOT)

What to check

  • Read freeze-frame data and confirming operating conditions when code set (engine temp, load, RPM, commanded EGR duty)
  • Use scan tool to command EGR open/closed and observe live data (EGR position, DPFE, MAP, EGR temp)
  • Visually inspect EGR valve, actuator, solenoid, vacuum hoses and electrical connectors for damage or leaks
  • Check vacuum supply (if vacuum system) for presence and leakage under command
  • Backprobe and monitor EGR valve position sensor or actuator signal during commanded cycles
  • Inspect and test DPFE/differential pressure or MAP sensor signals for plausibility

Signal parameters

  • EGR commanded vs actual: when commanded open, EGR position signal should change and remain stable
  • DPFE/differential pressure: should show increased differential when EGR is commanded open
  • MAP: small drop in manifold absolute pressure or transient change when EGR opens at part load
  • EGR temperature (if equipped): downstream temp should rise slightly when hot exhaust gas is recirculated
  • Vacuum at EGR (vacuum systems): vacuum present when solenoid energized/commanded
  • EGR solenoid coil supply: 12 V supply and switching ground from ECM when commanded (verify with meter/scan tool)

Diagnostic algorithm

  1. Verify the code and capture freeze-frame data. Note engine coolant temp, load, RPM and conditions when P0401 set.
  2. With a capable scan tool, command the EGR valve open/closed while monitoring EGR position, DPFE (or MAP), and EGR temp. Observe whether feedback changes as commanded.
  3. If EGR does not move when commanded, check actuator type: for vacuum systems test vacuum source and control solenoid; for electronic actuators check power, ground and control signal with connector connected.
  4. Inspect wiring and connectors for corrosion, broken wires, or pins pushed out. Wiggle-test while monitoring live data to detect intermittent faults.
  5. Inspect EGR valve and passages for carbon buildup. Remove valve for visual check and clean passages if clogged. On vehicles with EGR coolers, inspect cooler for blockage.
  6. Test DPFE/differential pressure or MAP sensor operation: compare sensor response to commanded EGR and known-good patterns. Replace sensor if out of range or nonresponsive.
  7. If cleaning restores movement but code returns, consider replacing EGR valve/actuator or EGR cooler as needed. After repair clear codes and perform a road test under conditions that previously set the code.
  8. If all hardware and sensors test OK but ECM logic persists, verify software updates/TSBs for EGR strategy; consult manufacturer procedures before replacing ECM.

Likely causes

  • Carbon/clogging in valve, passages, or EGR cooler (most common)
  • EGR valve not actuating due to failed solenoid or vacuum supply
  • Wiring/connectors to EGR actuator or feedback sensors are damaged or corroded
  • DPFE/differential pressure sensor or MAP sensor giving incorrect readings
  • EGR valve position sensor failed or out of tolerance

Fault status

⚠️ Status
P0401 — Insufficient exhaust gas recirculation flow detected. ECM commanded EGR but measured EGR flow/feedback is below expected threshold. Inspect EGR valve, passages, control solenoid/vacuum, and feedback sensors (DPFE/MAP/EGR position/temperature).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

Similar codes

P0400 P0402 P0403 P0404 P0405
Repair manuals

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Code

P0401

Generic P — Powertrain

EGR A Flow Insufficient Detected

Brand: Generic
Type: P — Powertrain
Views: UK: 45 EN: 349 RU: 155
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Carbon buildup/clogged EGR passages or EGR cooler
  • EGR valve stuck closed or mechanically seized
  • Failed EGR valve (electrical or vacuum-actuated)
  • Faulty EGR vacuum supply solenoid or hose leaks (vacuum systems)
  • Loss of electrical drive to EGR actuator (wiring, connector, fuse)
  • Defective or incorrect feedback from MAP, DPFE (differential pressure), EGR valve position sensor, or EGR temperature sensor

Symptoms

  • Check Engine Light (MIL) illuminated; code P0401 stored
  • Poor idle, hesitation or stumble under light load
  • Slight roughness or increased NOx emissions
  • Possible reduced fuel economy or increased combustion knock under some conditions
  • Engine may run normally at wide-open-throttle (EGR usually disabled at WOT)

What to check

  • Read freeze-frame data and confirming operating conditions when code set (engine temp, load, RPM, commanded EGR duty)
  • Use scan tool to command EGR open/closed and observe live data (EGR position, DPFE, MAP, EGR temp)
  • Visually inspect EGR valve, actuator, solenoid, vacuum hoses and electrical connectors for damage or leaks
  • Check vacuum supply (if vacuum system) for presence and leakage under command
  • Backprobe and monitor EGR valve position sensor or actuator signal during commanded cycles
  • Inspect and test DPFE/differential pressure or MAP sensor signals for plausibility

Signal parameters

  • EGR commanded vs actual: when commanded open, EGR position signal should change and remain stable
  • DPFE/differential pressure: should show increased differential when EGR is commanded open
  • MAP: small drop in manifold absolute pressure or transient change when EGR opens at part load
  • EGR temperature (if equipped): downstream temp should rise slightly when hot exhaust gas is recirculated
  • Vacuum at EGR (vacuum systems): vacuum present when solenoid energized/commanded
  • EGR solenoid coil supply: 12 V supply and switching ground from ECM when commanded (verify with meter/scan tool)

Diagnostic algorithm

  1. Verify the code and capture freeze-frame data. Note engine coolant temp, load, RPM and conditions when P0401 set.
  2. With a capable scan tool, command the EGR valve open/closed while monitoring EGR position, DPFE (or MAP), and EGR temp. Observe whether feedback changes as commanded.
  3. If EGR does not move when commanded, check actuator type: for vacuum systems test vacuum source and control solenoid; for electronic actuators check power, ground and control signal with connector connected.
  4. Inspect wiring and connectors for corrosion, broken wires, or pins pushed out. Wiggle-test while monitoring live data to detect intermittent faults.
  5. Inspect EGR valve and passages for carbon buildup. Remove valve for visual check and clean passages if clogged. On vehicles with EGR coolers, inspect cooler for blockage.
  6. Test DPFE/differential pressure or MAP sensor operation: compare sensor response to commanded EGR and known-good patterns. Replace sensor if out of range or nonresponsive.
  7. If cleaning restores movement but code returns, consider replacing EGR valve/actuator or EGR cooler as needed. After repair clear codes and perform a road test under conditions that previously set the code.
  8. If all hardware and sensors test OK but ECM logic persists, verify software updates/TSBs for EGR strategy; consult manufacturer procedures before replacing ECM.

Likely causes

  • Carbon/clogging in valve, passages, or EGR cooler (most common)
  • EGR valve not actuating due to failed solenoid or vacuum supply
  • Wiring/connectors to EGR actuator or feedback sensors are damaged or corroded
  • DPFE/differential pressure sensor or MAP sensor giving incorrect readings
  • EGR valve position sensor failed or out of tolerance

Fault status

⚠️ Status
P0401 — Insufficient exhaust gas recirculation flow detected. ECM commanded EGR but measured EGR flow/feedback is below expected threshold. Inspect EGR valve, passages, control solenoid/vacuum, and feedback sensors (DPFE/MAP/EGR position/temperature).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

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P0400 P0402 P0403 P0404 P0405
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Code

P0401

GWM P — Powertrain

- Exhaust gas recirculation system too low

Brand: GWM
Type: P — Powertrain
Views: UK: 21 EN: 28 RU: 63
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Carbon buildup/clogged EGR passages or EGR cooler
  • EGR valve stuck closed or mechanically seized
  • Failed EGR valve (electrical or vacuum-actuated)
  • Faulty EGR vacuum supply solenoid or hose leaks (vacuum systems)
  • Loss of electrical drive to EGR actuator (wiring, connector, fuse)
  • Defective or incorrect feedback from MAP, DPFE (differential pressure), EGR valve position sensor, or EGR temperature sensor

Symptoms

  • Check Engine Light (MIL) illuminated; code P0401 stored
  • Poor idle, hesitation or stumble under light load
  • Slight roughness or increased NOx emissions
  • Possible reduced fuel economy or increased combustion knock under some conditions
  • Engine may run normally at wide-open-throttle (EGR usually disabled at WOT)

What to check

  • Read freeze-frame data and confirming operating conditions when code set (engine temp, load, RPM, commanded EGR duty)
  • Use scan tool to command EGR open/closed and observe live data (EGR position, DPFE, MAP, EGR temp)
  • Visually inspect EGR valve, actuator, solenoid, vacuum hoses and electrical connectors for damage or leaks
  • Check vacuum supply (if vacuum system) for presence and leakage under command
  • Backprobe and monitor EGR valve position sensor or actuator signal during commanded cycles
  • Inspect and test DPFE/differential pressure or MAP sensor signals for plausibility

Signal parameters

  • EGR commanded vs actual: when commanded open, EGR position signal should change and remain stable
  • DPFE/differential pressure: should show increased differential when EGR is commanded open
  • MAP: small drop in manifold absolute pressure or transient change when EGR opens at part load
  • EGR temperature (if equipped): downstream temp should rise slightly when hot exhaust gas is recirculated
  • Vacuum at EGR (vacuum systems): vacuum present when solenoid energized/commanded
  • EGR solenoid coil supply: 12 V supply and switching ground from ECM when commanded (verify with meter/scan tool)

Diagnostic algorithm

  1. Verify the code and capture freeze-frame data. Note engine coolant temp, load, RPM and conditions when P0401 set.
  2. With a capable scan tool, command the EGR valve open/closed while monitoring EGR position, DPFE (or MAP), and EGR temp. Observe whether feedback changes as commanded.
  3. If EGR does not move when commanded, check actuator type: for vacuum systems test vacuum source and control solenoid; for electronic actuators check power, ground and control signal with connector connected.
  4. Inspect wiring and connectors for corrosion, broken wires, or pins pushed out. Wiggle-test while monitoring live data to detect intermittent faults.
  5. Inspect EGR valve and passages for carbon buildup. Remove valve for visual check and clean passages if clogged. On vehicles with EGR coolers, inspect cooler for blockage.
  6. Test DPFE/differential pressure or MAP sensor operation: compare sensor response to commanded EGR and known-good patterns. Replace sensor if out of range or nonresponsive.
  7. If cleaning restores movement but code returns, consider replacing EGR valve/actuator or EGR cooler as needed. After repair clear codes and perform a road test under conditions that previously set the code.
  8. If all hardware and sensors test OK but ECM logic persists, verify software updates/TSBs for EGR strategy; consult manufacturer procedures before replacing ECM.

Likely causes

  • Carbon/clogging in valve, passages, or EGR cooler (most common)
  • EGR valve not actuating due to failed solenoid or vacuum supply
  • Wiring/connectors to EGR actuator or feedback sensors are damaged or corroded
  • DPFE/differential pressure sensor or MAP sensor giving incorrect readings
  • EGR valve position sensor failed or out of tolerance

Fault status

⚠️ Status
P0401 — Insufficient exhaust gas recirculation flow detected. ECM commanded EGR but measured EGR flow/feedback is below expected threshold. Inspect EGR valve, passages, control solenoid/vacuum, and feedback sensors (DPFE/MAP/EGR position/temperature).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

Similar codes

P0400 P0402 P0403 P0404 P0405
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Code

P0401

HUMMER P — Powertrain

Exhaust Gas Recirculation (EGR) Flow Insufficient

Brand: HUMMER
Type: P — Powertrain
Views: UK: 25 EN: 48 RU: 104
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Carbon buildup/clogged EGR passages or EGR cooler
  • EGR valve stuck closed or mechanically seized
  • Failed EGR valve (electrical or vacuum-actuated)
  • Faulty EGR vacuum supply solenoid or hose leaks (vacuum systems)
  • Loss of electrical drive to EGR actuator (wiring, connector, fuse)
  • Defective or incorrect feedback from MAP, DPFE (differential pressure), EGR valve position sensor, or EGR temperature sensor

Symptoms

  • Check Engine Light (MIL) illuminated; code P0401 stored
  • Poor idle, hesitation or stumble under light load
  • Slight roughness or increased NOx emissions
  • Possible reduced fuel economy or increased combustion knock under some conditions
  • Engine may run normally at wide-open-throttle (EGR usually disabled at WOT)

What to check

  • Read freeze-frame data and confirming operating conditions when code set (engine temp, load, RPM, commanded EGR duty)
  • Use scan tool to command EGR open/closed and observe live data (EGR position, DPFE, MAP, EGR temp)
  • Visually inspect EGR valve, actuator, solenoid, vacuum hoses and electrical connectors for damage or leaks
  • Check vacuum supply (if vacuum system) for presence and leakage under command
  • Backprobe and monitor EGR valve position sensor or actuator signal during commanded cycles
  • Inspect and test DPFE/differential pressure or MAP sensor signals for plausibility

Signal parameters

  • EGR commanded vs actual: when commanded open, EGR position signal should change and remain stable
  • DPFE/differential pressure: should show increased differential when EGR is commanded open
  • MAP: small drop in manifold absolute pressure or transient change when EGR opens at part load
  • EGR temperature (if equipped): downstream temp should rise slightly when hot exhaust gas is recirculated
  • Vacuum at EGR (vacuum systems): vacuum present when solenoid energized/commanded
  • EGR solenoid coil supply: 12 V supply and switching ground from ECM when commanded (verify with meter/scan tool)

Diagnostic algorithm

  1. Verify the code and capture freeze-frame data. Note engine coolant temp, load, RPM and conditions when P0401 set.
  2. With a capable scan tool, command the EGR valve open/closed while monitoring EGR position, DPFE (or MAP), and EGR temp. Observe whether feedback changes as commanded.
  3. If EGR does not move when commanded, check actuator type: for vacuum systems test vacuum source and control solenoid; for electronic actuators check power, ground and control signal with connector connected.
  4. Inspect wiring and connectors for corrosion, broken wires, or pins pushed out. Wiggle-test while monitoring live data to detect intermittent faults.
  5. Inspect EGR valve and passages for carbon buildup. Remove valve for visual check and clean passages if clogged. On vehicles with EGR coolers, inspect cooler for blockage.
  6. Test DPFE/differential pressure or MAP sensor operation: compare sensor response to commanded EGR and known-good patterns. Replace sensor if out of range or nonresponsive.
  7. If cleaning restores movement but code returns, consider replacing EGR valve/actuator or EGR cooler as needed. After repair clear codes and perform a road test under conditions that previously set the code.
  8. If all hardware and sensors test OK but ECM logic persists, verify software updates/TSBs for EGR strategy; consult manufacturer procedures before replacing ECM.

Likely causes

  • Carbon/clogging in valve, passages, or EGR cooler (most common)
  • EGR valve not actuating due to failed solenoid or vacuum supply
  • Wiring/connectors to EGR actuator or feedback sensors are damaged or corroded
  • DPFE/differential pressure sensor or MAP sensor giving incorrect readings
  • EGR valve position sensor failed or out of tolerance

Fault status

⚠️ Status
P0401 — Insufficient exhaust gas recirculation flow detected. ECM commanded EGR but measured EGR flow/feedback is below expected threshold. Inspect EGR valve, passages, control solenoid/vacuum, and feedback sensors (DPFE/MAP/EGR position/temperature).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

Similar codes

P0400 P0402 P0403 P0404 P0405
Repair manuals

Manual library for HUMMER

138

Browse 138 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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Code

P0401

LAND ROVER P — Powertrain

Insufficient exhaust gas recirculation flow detected

Brand: LAND ROVER
Type: P — Powertrain
Views: UK: 22 EN: 42 RU: 98
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Carbon buildup/clogged EGR passages or EGR cooler
  • EGR valve stuck closed or mechanically seized
  • Failed EGR valve (electrical or vacuum-actuated)
  • Faulty EGR vacuum supply solenoid or hose leaks (vacuum systems)
  • Loss of electrical drive to EGR actuator (wiring, connector, fuse)
  • Defective or incorrect feedback from MAP, DPFE (differential pressure), EGR valve position sensor, or EGR temperature sensor

Symptoms

  • Check Engine Light (MIL) illuminated; code P0401 stored
  • Poor idle, hesitation or stumble under light load
  • Slight roughness or increased NOx emissions
  • Possible reduced fuel economy or increased combustion knock under some conditions
  • Engine may run normally at wide-open-throttle (EGR usually disabled at WOT)

What to check

  • Read freeze-frame data and confirming operating conditions when code set (engine temp, load, RPM, commanded EGR duty)
  • Use scan tool to command EGR open/closed and observe live data (EGR position, DPFE, MAP, EGR temp)
  • Visually inspect EGR valve, actuator, solenoid, vacuum hoses and electrical connectors for damage or leaks
  • Check vacuum supply (if vacuum system) for presence and leakage under command
  • Backprobe and monitor EGR valve position sensor or actuator signal during commanded cycles
  • Inspect and test DPFE/differential pressure or MAP sensor signals for plausibility

Signal parameters

  • EGR commanded vs actual: when commanded open, EGR position signal should change and remain stable
  • DPFE/differential pressure: should show increased differential when EGR is commanded open
  • MAP: small drop in manifold absolute pressure or transient change when EGR opens at part load
  • EGR temperature (if equipped): downstream temp should rise slightly when hot exhaust gas is recirculated
  • Vacuum at EGR (vacuum systems): vacuum present when solenoid energized/commanded
  • EGR solenoid coil supply: 12 V supply and switching ground from ECM when commanded (verify with meter/scan tool)

Diagnostic algorithm

  1. Verify the code and capture freeze-frame data. Note engine coolant temp, load, RPM and conditions when P0401 set.
  2. With a capable scan tool, command the EGR valve open/closed while monitoring EGR position, DPFE (or MAP), and EGR temp. Observe whether feedback changes as commanded.
  3. If EGR does not move when commanded, check actuator type: for vacuum systems test vacuum source and control solenoid; for electronic actuators check power, ground and control signal with connector connected.
  4. Inspect wiring and connectors for corrosion, broken wires, or pins pushed out. Wiggle-test while monitoring live data to detect intermittent faults.
  5. Inspect EGR valve and passages for carbon buildup. Remove valve for visual check and clean passages if clogged. On vehicles with EGR coolers, inspect cooler for blockage.
  6. Test DPFE/differential pressure or MAP sensor operation: compare sensor response to commanded EGR and known-good patterns. Replace sensor if out of range or nonresponsive.
  7. If cleaning restores movement but code returns, consider replacing EGR valve/actuator or EGR cooler as needed. After repair clear codes and perform a road test under conditions that previously set the code.
  8. If all hardware and sensors test OK but ECM logic persists, verify software updates/TSBs for EGR strategy; consult manufacturer procedures before replacing ECM.

Likely causes

  • Carbon/clogging in valve, passages, or EGR cooler (most common)
  • EGR valve not actuating due to failed solenoid or vacuum supply
  • Wiring/connectors to EGR actuator or feedback sensors are damaged or corroded
  • DPFE/differential pressure sensor or MAP sensor giving incorrect readings
  • EGR valve position sensor failed or out of tolerance

Fault status

⚠️ Status
P0401 — Insufficient exhaust gas recirculation flow detected. ECM commanded EGR but measured EGR flow/feedback is below expected threshold. Inspect EGR valve, passages, control solenoid/vacuum, and feedback sensors (DPFE/MAP/EGR position/temperature).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

Similar codes

P0400 P0402 P0403 P0404 P0405
320

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LAND ROVER

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Code

P0401

MITSUBISHI P — Powertrain

EGR flow insufficient

Brand: MITSUBISHI
Type: P — Powertrain
Views: UK: 34 EN: 48 RU: 102
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Carbon buildup/clogged EGR passages or EGR cooler
  • EGR valve stuck closed or mechanically seized
  • Failed EGR valve (electrical or vacuum-actuated)
  • Faulty EGR vacuum supply solenoid or hose leaks (vacuum systems)
  • Loss of electrical drive to EGR actuator (wiring, connector, fuse)
  • Defective or incorrect feedback from MAP, DPFE (differential pressure), EGR valve position sensor, or EGR temperature sensor

Symptoms

  • Check Engine Light (MIL) illuminated; code P0401 stored
  • Poor idle, hesitation or stumble under light load
  • Slight roughness or increased NOx emissions
  • Possible reduced fuel economy or increased combustion knock under some conditions
  • Engine may run normally at wide-open-throttle (EGR usually disabled at WOT)

What to check

  • Read freeze-frame data and confirming operating conditions when code set (engine temp, load, RPM, commanded EGR duty)
  • Use scan tool to command EGR open/closed and observe live data (EGR position, DPFE, MAP, EGR temp)
  • Visually inspect EGR valve, actuator, solenoid, vacuum hoses and electrical connectors for damage or leaks
  • Check vacuum supply (if vacuum system) for presence and leakage under command
  • Backprobe and monitor EGR valve position sensor or actuator signal during commanded cycles
  • Inspect and test DPFE/differential pressure or MAP sensor signals for plausibility

Signal parameters

  • EGR commanded vs actual: when commanded open, EGR position signal should change and remain stable
  • DPFE/differential pressure: should show increased differential when EGR is commanded open
  • MAP: small drop in manifold absolute pressure or transient change when EGR opens at part load
  • EGR temperature (if equipped): downstream temp should rise slightly when hot exhaust gas is recirculated
  • Vacuum at EGR (vacuum systems): vacuum present when solenoid energized/commanded
  • EGR solenoid coil supply: 12 V supply and switching ground from ECM when commanded (verify with meter/scan tool)

Diagnostic algorithm

  1. Verify the code and capture freeze-frame data. Note engine coolant temp, load, RPM and conditions when P0401 set.
  2. With a capable scan tool, command the EGR valve open/closed while monitoring EGR position, DPFE (or MAP), and EGR temp. Observe whether feedback changes as commanded.
  3. If EGR does not move when commanded, check actuator type: for vacuum systems test vacuum source and control solenoid; for electronic actuators check power, ground and control signal with connector connected.
  4. Inspect wiring and connectors for corrosion, broken wires, or pins pushed out. Wiggle-test while monitoring live data to detect intermittent faults.
  5. Inspect EGR valve and passages for carbon buildup. Remove valve for visual check and clean passages if clogged. On vehicles with EGR coolers, inspect cooler for blockage.
  6. Test DPFE/differential pressure or MAP sensor operation: compare sensor response to commanded EGR and known-good patterns. Replace sensor if out of range or nonresponsive.
  7. If cleaning restores movement but code returns, consider replacing EGR valve/actuator or EGR cooler as needed. After repair clear codes and perform a road test under conditions that previously set the code.
  8. If all hardware and sensors test OK but ECM logic persists, verify software updates/TSBs for EGR strategy; consult manufacturer procedures before replacing ECM.

Likely causes

  • Carbon/clogging in valve, passages, or EGR cooler (most common)
  • EGR valve not actuating due to failed solenoid or vacuum supply
  • Wiring/connectors to EGR actuator or feedback sensors are damaged or corroded
  • DPFE/differential pressure sensor or MAP sensor giving incorrect readings
  • EGR valve position sensor failed or out of tolerance

Fault status

⚠️ Status
P0401 — Insufficient exhaust gas recirculation flow detected. ECM commanded EGR but measured EGR flow/feedback is below expected threshold. Inspect EGR valve, passages, control solenoid/vacuum, and feedback sensors (DPFE/MAP/EGR position/temperature).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

Similar codes

P0400 P0402 P0403 P0404 P0405
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

MITSUBISHI

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