P0402: Exhaust Gas Recirculation A Flow Excessive Detected
What to do
Expect a rough or surging idle and possible stalling when coming to a stop, easing once moving. Driveable but unpleasant; worth fixing rather than living with.
What this code means
More exhaust gas is entering the intake than was commanded. Because recirculated gas is inert, an excess of it behaves like a large vacuum leak that contains no oxygen: the engine runs rough, stumbles, and may stall when returning to idle. The distinguishing feature against an ordinary vacuum leak is that fuel trim does not swing lean — the module is not seeing unmetered air, it is seeing displaced air.
Almost always this is a valve that is not closing rather than one opening too far. Carbon on the seat holds it fractionally open, and at idle even a small opening is a large proportion of total flow, which is why the symptom is worst at idle and disappears under load. A valve stuck open at idle is also one of the few EGR faults a driver actually notices.
Likely causes
Start here
- EGR valve stuck open · moderate
- Failed EGR vacuum solenoid · easy
Less common
- Damaged EGR valve seat or diaphragm · moderate
- Faulty exhaust gas differential pressure sensor · easy
- Faulty EGR position sensor · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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