OBD-II code · Powertrain (generic)
P0400 Exhaust Gas Recirculation Flow Malfunction
A general fault has been detected in the exhaust gas recirculation (EGR) system. EGR routes a portion of exhaust back into the intake to reduce combustion temperature and NOx emissions. Most EGR codes today are caused by carbon buildup blocking the valve.
Is it safe to drive with P0400?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyEGR valve clogged with carbon
- PossibleIntake EGR passages blocked
- Less likelyDPFE / EGR position sensor failed
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 1–5 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Egr Valve, Egr Cooler, Dpfe Sensor
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.