Fault-Code Library · EGR
P0401: Exhaust-gas recirculation flow insufficient
Measured or inferred EGR flow is lower than the controller expects.
Common symptoms
- •Engine warning light
- •Reduced power
- •Knock or harsh combustion
- •Emissions fault
Likely causes
- •Carbon-blocked EGR passages
- •Sticking EGR valve
- •Sensor plausibility fault
- •Vacuum or actuator problem
First checks
- •Command the EGR while monitoring airflow
- •Inspect passages and cooler for restriction
- •Verify pressure and temperature sensors
Important
Cleaning only the valve may not fix blocked passages or a failed control system.
A fault code identifies a detected condition, not a failed part. Confirm manufacturer-specific subcodes and live data.