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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

Detailed page for trouble code P0401.

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Code

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: 27 EN: 41 RU: 80
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

Generic P — Powertrain

EGR A Flow Insufficient Detected

Brand: Generic
Type: P — Powertrain
Views: UK: 28 EN: 42 RU: 89
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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Key sections:
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Short description

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199,00 UAH
Contents
Key sections:
  • 00 - Technical data
  • 1 Engine number
  • 2 Engine data (Codes: BBK / BHF; 4.163 l; 253 kW @7000 rpm; torque 410–420 Nm; bore 84.5 mm; stroke 92.8 mm; compression ratio 11.5; RON 98)
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  • 4 General repair instructions (cleanliness, fuel system, contact corrosion)
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  • 1.1 Removing engine (tools, drain fluids, remove bumper, lock carrier, disconnect wiring, fuel, coolant, A/C lines, suspension components, propshaft, exhaust, support engine on platform, lower assembly)
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Workshop Manual
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Short description

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Contents
Key sections:
  • 01 - Self-diagnosis, electrical checks
  • 1 Auxiliary heater self-diagnosis
  • 1.1 Technical data of self-diagnosis
  • 1.2 Function
  • 1.3 Fault recognition
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  • 1.5 Technical data of self-diagnosis
  • 1.6 Test requirements for self-diagnosis
  • 1.7 Safety precautions
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  • 2.1 Connecting vehicle diagnostic VAS 5051A/K-wire adapter
  • 2.1.1 Control unit identification
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Audi A4 / A4 Cabriolet (1.8T 4‑cyl turbo) — Motronic Injection & Ignition System Service Manual (Edition 01.2015)

Workshop Manual
Years: 2001 Manual in English Pages: 34 851.0 KB
Short description

Service manual for Audi A4 (2001‑) and A4 Cabriolet (2003‑) with 1.8L 4‑cylinder turbo engines. Covers Motronic fuel injection and ignition systems, diagnostic and maintenance procedures. Includes technical data, removal/installation steps and system checks.

199,00 UAH
Contents
Key sections:
  • 24 - Mixture preparation - injection
  • 1 Safety precautions and rules for cleanliness
  • 1.1 General notes on self-diagnosis
  • 1.2 Safety precautions when using testers and measuring instruments during a road test
  • 1.3 Rules for cleanliness and instructions for working on fuel system
  • 1.4 Checking vacuum system
  • 2 Injection system
  • 2.1 Technical data
  • 2.2 Overview of fitting locations - injection system
  • 3 Intake manifold
  • 3.1 Exploded view - intake manifold
  • 3.2 Removing and installing intake manifold
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Audi A8 (2003) — Electrical System Workshop Manual (Edition 08.2014)

Workshop Manual
Years: 2003 Manual in English Pages: 369 9.1 MB
Short description

Comprehensive workshop manual for the Audi A8 (2003) electrical system — Edition 08.2014. Covers battery, alternator, starter, instrument cluster, wiper/washer systems, exterior/interior lighting and wiring repair procedures with step-by-step illustrations. Includes diagnostic and adjustment procedures and torque/data specifications.

199,00 UAH
Contents
Key sections:
  • 27 - Starter, current supply, CCS
  • 1 Contact corrosion
  • 2 Battery
  • 2.1 Battery - general notes
  • 2.2 Maintenance-free batteries
  • 2.3 Disconnecting and connecting battery
  • 2.4 Removing and installing battery
  • - Remove luggage compartment side trim (right-side)
  • - Connect battery charger for back-up power
  • - Detach earth and positive cables, central venting hose
  • - Remove battery retainer plate and lift battery out
  • - Installation notes, adaptation via Vehicle diagnostic tester
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Audi Q4 e-tron (Type F4) - Self-study Programme SSP 685

Workshop Manual
Years: 2021 Manual in English Pages: 186 82.7 MB
Short description

Official Audi Service Training self‑study programme SSP 685 for the Audi Q4 e‑tron (Type F4). Covers body, power units, power transmission, running gear, electrics & electronics, high‑voltage system, thermal management, driver assist and infotainment. Intended for internal service training and technical familiarisation; not a workshop repair manual.

199,00 UAH
Contents
Key sections:
  • Introduction
  • - Introduction to Audi Q4 e-tron
  • - Dimensions
  • Body
  • - Body structure and materials
  • - Joining techniques
  • - Securing high-voltage battery and force progression
  • - Body assembly (doors, rear lid, panoramic sunroof)
  • - Dash panel and centre console
  • Power units
  • - Technical data: rear electric motor (VX90)
  • - Technical data: front electric motor (VX89)
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Audi Q8 (2018) — Electrical System Workshop Manual (Edition 05.2019)

Workshop Manual
Years: 2018 Manual in English Pages: 645 14.8 MB
Short description

Workshop manual for the Audi Q8 (2018) — Electrical System. Includes technical data, safety notes and step‑by‑step repair procedures for battery/charging, starter/alternator, lighting, washer/wiper and wiring. Edition 05.2019.

199,00 UAH
Contents
Key sections:
  • 00 - Technical data
  • 1 Safety precautions
  • 1.1 Safety precautions when working on vehicles with start/stop system
  • 1.2 Safety precautions when using testers and measuring instruments during a road test
  • 1.3 Notes on use and safety for LED headlights and Audi laser lights
  • 2 Repair notes
  • 2.1 Rules for cleanliness
  • 2.2 General notes
  • 2.3 Contact corrosion
  • 2.4 ESD (electrostatic discharge) workplace
  • 2.5 Routing and attachment of lines and wiring
  • 2.6 Identification plates
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Audi Servicing Manual — 7‑Speed Dual Clutch Transmission 0CJ / 0CL / 0CK / 0DN / 0DP / 0HL (Edition 05.2018)

Workshop Manual
Years: 2008–2019 Manual in English Pages: 128 11.1 MB
Short description

Service manual for the 7‑Speed dual‑clutch (DSG) transmissions 0CJ/0CL/0CK/0DN/0DP/0HL fitted to various Audi models. Includes repair information, clutch and gearbox disassembly/assembly, mechatronic and hydraulic system procedures, seals and differential work. Edition 05.2018.

199,00 UAH
Contents
Key sections:
  • 00 - General, Technical Data
  • 1 Repair Information
  • 1.1 General Repair Information
  • 1.2 Contact Corrosion
  • 1.3 ATF Pump, Deactivating and Draining the Hydraulic Pump Reservoir
  • 2 Rules for Cleanliness when Working on DSG® Transmission
  • 30 - Clutch
  • 1 Clutch
  • 1.1 Overview - Flywheel and Dual Clutch
  • 1.2 Flywheel, Removing and Installing
  • 1.3 Dual Clutch, Removing and Installing
  • 1.4 Input Shaft Seal, Replacing
Buy
LAND ROVER 3

Land Rover Defender 300Tdi — Workshop Manual (1996 model year)

Workshop Manual
Defender 300Tdi Years: 1996 Manual in English 7.5 MB
Short description

Official workshop manual for the Land Rover Defender 300Tdi (from 1996 model year). Contains specifications, adjustment, fault diagnosis and step-by-step repair and overhaul procedures for engine, transmission, axles, suspension, brakes, electrical and body. Intended for dealer workshops and trained technicians.

199,00 UAH
Contents
Key sections:
  • 01 INTRODUCTION
  • 04 GENERAL SPECIFICATION DATA
  • 05 ENGINE TUNING DATA
  • 07 GENERAL FITTING REMINDERS
  • 09 LUBRICANTS, FLUIDS AND CAPACITIES
  • 10 MAINTENANCE
  • 12 ENGINE Tdi
  • - Description and operation
  • - Fault diagnosis
  • - Adjustment
  • - Repair and overhaul procedures
  • 19 FUEL SYSTEM Tdi
Buy

Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)

Workshop Manual
Defender Years: 1999–2002 Manual in English 7.6 MB
Short description

Workshop Manual Supplement and Body Repair Manual for the Land Rover Defender. Includes general specifications, maintenance schedules, tuning data and step‑by‑step repair procedures for engine, transmission, suspension, brakes, electrical and body repairs. Covers Defender models from 1999 and 2002 model years.

199,00 UAH
Contents
Key sections:
  • 01 - INTRODUCTION
  • - Introduction
  • - Dimensions
  • - References
  • - Repairs and replacements
  • - Poisonous substances
  • - Fuel handling precautions
  • - Synthetic rubber
  • - Recommended sealants
  • - Used engine oil precautions
  • - Accessories and conversions
  • - Wheels and tyres
Buy

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
Contents
Key sections:
  • 1 INTRODUCTION
  • 1.1 About this document
  • 1.2 Battery voltage
  • 1.3 Electrical precautions
  • 1.4 Battery disconnecting / charging
  • 1.5 Disciplines / greases
  • 1.6 Abbreviations
  • 1.7 HeVAC, sensors abbreviations
  • 1.8 How to use this document
  • 1.9 Connector detail format
  • 1.10 Fault diagnosis
  • 1.11 Wire colour codes
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Code

P0401

GWM P — Powertrain

- Exhaust gas recirculation system too low

Brand: GWM
Type: P — Powertrain
Views: UK: 2 EN: 4 RU: 14
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: 9 EN: 23 RU: 54
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
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

P0401

LAND ROVER P — Powertrain

Insufficient exhaust gas recirculation flow detected

Brand: LAND ROVER
Type: P — Powertrain
Views: UK: 6 EN: 20 RU: 48
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
Workshop Manuals

Repair manuals for LAND ROVER

3

Land Rover Defender 300Tdi — Workshop Manual (1996 model year)

Workshop Manual
Defender 300Tdi Years: 1996 Manual in English 7.5 MB
Short description

Official workshop manual for the Land Rover Defender 300Tdi (from 1996 model year). Contains specifications, adjustment, fault diagnosis and step-by-step repair and overhaul procedures for engine, transmission, axles, suspension, brakes, electrical and body. Intended for dealer workshops and trained technicians.

199,00 UAH
Contents
Key sections:
  • 01 INTRODUCTION
  • 04 GENERAL SPECIFICATION DATA
  • 05 ENGINE TUNING DATA
  • 07 GENERAL FITTING REMINDERS
  • 09 LUBRICANTS, FLUIDS AND CAPACITIES
  • 10 MAINTENANCE
  • 12 ENGINE Tdi
  • - Description and operation
  • - Fault diagnosis
  • - Adjustment
  • - Repair and overhaul procedures
  • 19 FUEL SYSTEM Tdi
Buy

Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)

Workshop Manual
Defender Years: 1999–2002 Manual in English 7.6 MB
Short description

Workshop Manual Supplement and Body Repair Manual for the Land Rover Defender. Includes general specifications, maintenance schedules, tuning data and step‑by‑step repair procedures for engine, transmission, suspension, brakes, electrical and body repairs. Covers Defender models from 1999 and 2002 model years.

199,00 UAH
Contents
Key sections:
  • 01 - INTRODUCTION
  • - Introduction
  • - Dimensions
  • - References
  • - Repairs and replacements
  • - Poisonous substances
  • - Fuel handling precautions
  • - Synthetic rubber
  • - Recommended sealants
  • - Used engine oil precautions
  • - Accessories and conversions
  • - Wheels and tyres
Buy

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
Contents
Key sections:
  • 1 INTRODUCTION
  • 1.1 About this document
  • 1.2 Battery voltage
  • 1.3 Electrical precautions
  • 1.4 Battery disconnecting / charging
  • 1.5 Disciplines / greases
  • 1.6 Abbreviations
  • 1.7 HeVAC, sensors abbreviations
  • 1.8 How to use this document
  • 1.9 Connector detail format
  • 1.10 Fault diagnosis
  • 1.11 Wire colour codes
Buy
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

P0401

MITSUBISHI P — Powertrain

EGR flow insufficient

Brand: MITSUBISHI
Type: P — Powertrain
Views: UK: 12 EN: 25 RU: 57
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
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

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