P0400EGR A Flow
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. P0400 is the general flow fault of EGR system A, used where the module does not classify the error as too little (P0401) or too much (P0402). Ford petrol engines with a stepper-motor valve open and close the valve at steady part load and compare intake manifold pressure with and without EGR; too small a normalised difference (below 1.0) sets P0400, MIL after two trips. GM diesels use the code differently, for air-mass checks with excessive EGR rate. EGR is then usually switched off.
- What you may notice
- Check engine light on
- Pinging under load or rough idle, depending on direction
- Higher NOx, emission test failed
- Likely causes
- LikelyEGR passages or valve carboned up
- PossibleEGR valve stiff or faulty
- PossibleLeak in the intake or EGR pipe
- RareMAP or MAF sensor inaccurate
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.