Code result
P0400
Exhaust Gas Recirculation Flow Malfunction
Moderate severity
What it means
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?
Use caution
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical.
Most likely causes
EGR valve clogged with carbon
highOne of the most commonly reported causes for this code — check this first.
Intake EGR passages blocked
mediumA plausible cause — test and verify before replacing parts.
DPFE / EGR position sensor failed
lowLess common, but worth ruling out after the more likely causes.
Related help
Get the full diagnosis
Add your vehicle and see step-by-step repair help, recalls, and TSBs in Wrenchify.
Diagnose P0400 freeNo credit card required