P0402: Exhaust gas recirculation (EGR) flow excessive
The exhaust gas recirculation (EGR) system is flowing more exhaust than expected, often because the EGR valve doesn’t close fully.
Updated
What P0402 means
The EGR valve leads some exhaust gas back into the intake to lower the nitrogen oxide (NOx) emissions. The engine computer decides how much, depending on the engine speed and load: petrol engines use little or none at idle and under full load, diesels also use it at idle and light load.
When the engine computer sees more exhaust gas flowing than it asked for, often while it has commanded the valve shut, it stores P0402. It’s the opposite of P0401, too little flow.
Can I keep driving?
Drive gently
Drive gently and have it checked soon. Too much exhaust gas can make the engine run rough or lose power, and a petrol engine can stall when you slow down or stop, so leave extra room in traffic.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
Too much exhaust gas leaves too little fresh air to burn the fuel properly. A petrol engine can stumble or stall when you stop, at junctions or in slow traffic; a diesel may run rough, smoke or lose power.
Symptoms
- A rough or uneven idle.
- Stalling when slowing down or stopping.
- Hesitation when pulling away.
- Hard starting on some cars.
Common causes
- EGR valve stuck open, often by carbon. Carbon on the valve seat can keep it from closing.
- Faulty EGR control valve or position sensor. The part that opens the valve, or the sensor that reports its position, doesn’t do its job.
- Wiring fault. A damaged wire or corroded connector to the EGR valve or its sensor.
Typical fixes
- Have the EGR valve checked for carbon that holds it open, and cleaned or replaced.
- Have the valve’s control and position sensor checked, and their wiring.
- Clear the code after the repair. Under emissions readiness, the EGR self-test shows when the car has re-tested the system.
Questions
Can I drive with P0402?
Gently, and have it checked soon. Too much exhaust gas can make the engine run rough or lose power, and a petrol engine can stall when you slow down or stop, so leave extra room in traffic.
What is the difference between P0401 and P0402?
P0401 means too little exhaust gas flows back, often from carbon clogging the passages. P0402 means too much flows, often because the valve doesn’t close.