Exhaust gas recirculation
P0400
Exhaust Gas Recirculation Flow
The system that feeds a little exhaust back into the engine to lower emissions isn't flowing the way the computer expects.
Fine to drive
Can I keep driving? Yes, in most cases. It won't hurt the car in the short term, but get it fixed. A check engine light that's already on can't warn you about a new problem. It's safe to drive. You may notice pinging or a rough idle, and it will fail an emissions test.
Common causes
- Carbon blocking the EGR valve or its passages
- A failed EGR valve or position sensor
- A vacuum or wiring fault
Listed roughly from most to least likely. The same code can have different causes on different cars.
What to do
- Have the EGR valve and passages checked for carbon.
- Clean or replace the valve.
- Check the wiring and any vacuum lines.
General guidance. Your owner's manual wins. If a red warning light is on or the car drives differently, stop safely and get help.
Related codes
- P0401Exhaust Gas Recirculation Flow Insufficient Detected
- P0402Exhaust Gas Recirculation Flow Excessive Detected
- P0403Exhaust Gas Recirculation Control Circuit
- P0404Exhaust Gas Recirculation Control Circuit Range/Performance
- P0405Exhaust Gas Recirculation Sensor "A" Circuit Low
Track this automatically in Tagwell Auto
Tagwell Auto keeps your car's service dates and mileage, so when a code shows up you know what was done last. With a Bluetooth reader for the car's diagnostic port (called OBD-II), the phone app can read the code itself.