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EmissionsSeverity Medium: diagnose soon

P0402Exhaust Gas Recirculation "A" Flow Excessive Detected

What it means

More exhaust gas is flowing back than the ECU wants, typically because the EGR valve doesn't close. At idle this replaces fresh air and the engine runs rough.

Symptoms

  • Rough idle or stalling
  • Loss of power, sometimes limp mode
  • Black smoke (diesel) or pinging under load (petrol)

Common causes

  • EGR valve stuck open with carbon
  • Faulty EGR position sensor
  • Control solenoid stuck
  • Wrong vacuum routing

What to check first

  1. Compare requested and actual air mass at idle
  2. Inspect the valve for carbon holding it open
  3. Run the actuator test
Can I drive with P0402? Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.
Practise it: EGR valve stuck open (diesel) in the engine simulator shows this fault in live data, tests and on the scope.Open in the simulator

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

How to test the parts behind P0402

EGR valveWiring, typical values, multimeter and scope tests

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P0402: questions and answers

What does P0402 mean?

P0402: Exhaust Gas Recirculation "A" Flow Excessive Detected. More exhaust gas is flowing back than the ECU wants, typically because the EGR valve doesn't close. At idle this replaces fresh air and the engine runs rough.

What are the symptoms of P0402?

Rough idle or stalling. Loss of power, sometimes limp mode. Black smoke (diesel) or pinging under load (petrol).

What causes P0402?

EGR valve stuck open with carbon. Faulty EGR position sensor. Control solenoid stuck. Wrong vacuum routing.

How do you diagnose P0402?

1. Compare requested and actual air mass at idle 2. Inspect the valve for carbon holding it open 3. Run the actuator test

Can I drive with P0402?

Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.