OBD-II code guide
P0401 Exhaust Gas Recirculation Flow Insufficient
P0401 means the EGR system is not flowing as much exhaust gas as expected.
What it means
The engine computer commanded EGR flow but did not see the expected change.
Common symptoms
- Check engine light
- Pinging under load
- Poor acceleration
- Higher combustion temperature
- Sometimes no obvious symptom
Likely causes
- Clogged EGR passages
- Stuck EGR valve
- Vacuum control fault
- Sensor feedback problem
- Damaged wiring
First checks
- Inspect EGR passages for carbon blockage.
- Check valve control and position feedback.
- Look for vacuum hose faults where applicable.
- Do not replace the valve before checking clogged ports.