Back to lookup

Generic gasoline powertrain DTC / Exhaust gas recirculation

P0401: Exhaust gas recirculation flow insufficient detected

The controller detected less exhaust-gas recirculation flow than expected under its monitor conditions.

Generic definition
P0400

Likely cause paths · unconfirmed

A possible restricted EGR flow path

Carbon restriction or a flow-path issue can affect measured recirculation, but the code does not locate a restriction.

  • Note idle quality and when the warning returns.
  • Record any recent intake or exhaust work.

A possible EGR valve, sensor, or control-circuit issue

The valve, feedback signal, wiring, or control may be involved; the DTC alone does not isolate a component.

  • Save related circuit and air-flow codes.
  • Do not force the valve or disconnect wiring.

Likely causes and repair directions are general, conditional orientation. The SAE citation supports the generic DTC definition only; it does not validate these causes, tests, repairs, or fitment to a particular vehicle.

Conditional likely repairs

A code describes a monitored condition; it does not prove a failed part. Use these directions only after confirming the cause.

If confirmed: A possible restricted EGR flow path

If a flow test confirms restriction, service the verified passage according to OEM instructions and confirm flow.

Evidence to confirm

  • The prescribed flow test confirms inadequate flow.
  • The monitor completes after service.

If confirmed: A possible EGR valve, sensor, or control-circuit issue

If circuit or actuator testing confirms a control fault, repair the isolated wiring or component and repeat the system test.

Evidence to confirm

  • Circuit and command/feedback tests isolate the fault.
  • EGR response follows the commanded test after repair.

Guided evidence checks

  1. 01

    Record what happened

    Note when the warning appeared, what the vehicle was doing, and any recent service or change. Do not deliberately recreate an unsafe symptom.

  2. 02

    Make only a safe visual check

    Record warning behavior and drivability changes. Do not touch hot exhaust parts or remove an EGR component.

  3. 03

    Preserve scan-tool evidence

    Qualified technician

    Save the code status, freeze-frame, and available EGR command/feedback data.

  4. 04

    Confirm the system path

    Qualified technician

    A qualified technician should test EGR flow, passages, control circuit, and feedback using the exact vehicle procedure.

Code-specific symptom note

  • Code-specific symptoms are not verified by the cited definition. Record the driver’s actual observations separately.

This generic code reference is not an OEM procedure, does not confirm that a DTC applies to a particular make/model/engine, and is not a repair diagnosis. Follow vehicle-specific service information or consult a qualified technician.