Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.

P0402: Exhaust gas recirculation flow excessive detected

The engine computer has measured or inferred more EGR flow than it commanded.

What P0402 means

The engine computer has measured or inferred more EGR flow than it commanded. That may represent a valve stuck open, unwanted actuation or a misleading feedback signal rather than genuine excess flow.

Can I still drive?

Prompt attention is appropriate because excessive EGR can destabilise combustion, especially at idle. A short, gentle drive may be acceptable with a steady light and stable engine. Stop if the vehicle stalls or surges in traffic, runs very roughly, responds poorly to the throttle or shows a flashing or red warning.

Symptoms

  • Engine-management light.
  • Rough or unstable idle and surging.
  • Hesitation, reduced power or poor throttle response.
  • Stalling or difficult starting in severe cases.
  • No obvious symptom when the feedback signal is false.

Common causes

  • EGR valve held open by carbon or mechanical damage.
  • Faulty actuator or vacuum solenoid applying unwanted control.
  • Incorrect differential-pressure, position or other feedback-sensor signal.
  • Shorted wiring, connector corrosion or poor earth.
  • Pipe, intake or pressure disturbance affecting inferred flow.
  • Rare module software or hardware fault.

Safe first checks

  • Record all codes and freeze-frame data. Once cold, inspect the valve connector, visible loom and relevant vacuum hoses for damage or disconnection. Check pipe joints for cracks, loose fasteners or soot tracks. Avoid an extended road test if the engine repeatedly stalls. Before any valve replacement, compare commanded and actual position/flow using the correct diagnostic routine.

Typical UK fix cost

Expect £90–£180 for diagnosis. Cleaning or a simple vacuum/connector repair may total £150–£400; a valve, solenoid, sensor or wiring repair generally falls around £250–£900. Integrated cooler/valve assemblies and difficult access may reach £700–£1,500+.

Related models

This is a generic OBD-II code used across many makes and models. The exact test thresholds, component layout and repair route vary by engine and manufacturer, so check vehicle-specific technical information before ordering parts.

Related fault codes

Sources

A diagnostic trouble code identifies a system or circuit to investigate. It does not prove that a named part has failed. Preserve freeze-frame data and seek a vehicle-specific diagnosis before clearing the code.