Emission Control (Diesel)

P0401Exhaust Gas Recirculation Flow Insufficient Detected

Medium RiskDifficulty:Moderate1-4 hours
Is it safe to drive?
Short trips, with care

The car usually still drives but may go into limp mode. If neglected for long, the intake manifold and DPF soot up faster.

Will it pass inspection?
Risky

Smoke opacity may rise on a diesel, and going to inspection with the warning light on is risky. Deleting the EGR is illegal.

01 / 06

What does P0401 mean?

The EGR valve, which sends part of the exhaust back into the engine, can't deliver the requested flow. On diesels it's stuck with soot 80% of the time. Short city trips are the main cause. Clean first, replace second; deleting it is not a solution.

P0401 is stored when the ECU opens the EGR valve but doesn't see the expected change in intake pressure or MAF value. On diesels, soot building up in the EGR valve, EGR cooler and intake manifold blocks the flow. The valve's position sensor or motor can also fail.

02 / 06

How to fix P0401

Steps are ordered from cheapest to most expensive. If a step doesn't solve it, move to the next one, and don't let a garage replace parts blindly.

  1. 1

    Long drive / high-rev driving

    DIY

    With light sooting, 20-30 minutes on the motorway (around 3,000 rpm) can help the valve clean itself.

  2. 2

    EGR valve live data / adaptation test

    Pro job

    Compare requested and actual EGR position in diagnostics; run a valve actuation test.

  3. 3

    Remove and clean the EGR valve

    Pro job

    The valve is removed and cleaned of soot, followed by adaptation/relearn.

  4. 4

    Intake manifold and EGR passage cleaning

    Pro job

    With heavy sooting, the manifold is also removed and cleaned.

  5. 5

    EGR valve replacement

    Pro job

    Replaced if the code returns after cleaning or the valve motor is faulty.

Don't replace these first

  • Turbocharger
  • Injectors
  • DPF

These parts are often replaced unnecessarily for P0401. Don't spend money on them before doing the checks above.

03 / 06

P0401 symptoms

  • Check engine / malfunction indicator light
  • Limp mode (power restriction)
  • Rough idle
  • Black smoke
  • Flat spot when accelerating in gear

04 / 06

What causes P0401?

  • EGR valve clogged with sootVery high
  • Clogged EGR cooler / passagesMedium
  • Faulty EGR valve motor or position sensorMedium
  • Sooted intake manifoldMedium
  • Connector / wiring problemLow

05 / 06

Which cars commonly get P0401?

06 / 06

Frequently asked questions

What does fault code P0401 mean?

P0401 stands for “Exhaust Gas Recirculation Flow Insufficient Detected”. The EGR valve, which sends part of the exhaust back into the engine, can't deliver the requested flow. On diesels it's stuck with soot 80% of the time. Short city trips are the main cause. Clean first, replace second; deleting it is not a solution.

Can I drive with code P0401?

Short trips, with care. The car usually still drives but may go into limp mode. If neglected for long, the intake manifold and DPF soot up faster.

Will a car with code P0401 pass vehicle inspection?

Risky. Smoke opacity may rise on a diesel, and going to inspection with the warning light on is risky. Deleting the EGR is illegal.

Can I have the EGR deleted?

Deleting the EGR breaks emissions regulations and causes problems at inspection and in the emissions test. The permanent fix is cleaning or replacement.

Related codes

P0101P2002P0299