P0401 Code: Exhaust Gas Recirculation (EGR) Flow Insufficient Detected
🟠 Moderate severity · drivable
Drivable, but a clogged EGR system can cause pinging (detonation) under load and may fail an emissions test.
What P0401 means
The exhaust gas recirculation (EGR) system isn't flowing enough exhaust gas back into the intake. The EGR system reduces nitrogen-oxide emissions and lowers combustion temperature; when it's restricted, the computer detects too little flow.
Symptoms
- Check engine light is on
- Possible pinging or knocking under load
- Rough idle
- Failed emissions test (high NOx)
Common causes
- most common: Carbon-clogged EGR valve or passages
- common: Faulty EGR valve
- common: Faulty DPFE sensor (Ford and others)
- less common: Cracked or disconnected EGR vacuum line
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Remove and clean carbon from the EGR valve and passages | Yes | $20–100 |
| Replace the EGR valve | Yes | $100–400 |
| Replace a faulty DPFE sensor | Yes | $40–120 |
| Repair a cracked or disconnected vacuum line | Yes | $5–30 |
Frequently asked questions
Can I drive with a P0401 code?
Yes, but a restricted EGR system can cause pinging under load. Fix it before your next emissions test.
What is the most common cause of P0401?
Carbon buildup clogging the EGR valve and passages. Cleaning them often resolves it.
How much does it cost to fix a P0401?
Cleaning is $20–$100 DIY. A new EGR valve runs $100–$400 depending on the vehicle.
Related codes
P0402
P0402 Code: Exhaust Gas Recirculation (EGR) Flow Excessive Detected
P0404P0404 Code: Exhaust Gas Recirculation (EGR) Circuit Range/Performance
P0400P0400 Code: Exhaust Gas Recirculation (EGR) Flow Malfunction
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.