Severity: Moderate
Drivable, but it can cause more damage or poor economy. Get it checked within days.
What P0401 means
The computer did not see the EGR flow it expected. On diesels the EGR cooler and valve can clog with soot.
Symptoms
- Usually none
- Pinging under load on gas engines
- Higher NOx
Common causes
Most likely first
- 1Carbon-clogged EGR valve or passages
- 2Failed EGR valve or position sensor
- 3Plugged EGR cooler (diesel)
- 4Vacuum or control fault
How we diagnose it
- Command EGR and watch MAF/MAP response
- Inspect valve and passages for carbon
Every vehicle sets codes under its own conditions. We check the factory diagnostic steps and service bulletins for your VIN, so the repair targets the actual cause.