P0401EGR A Flow Insufficient Detected
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. P0401 means too little exhaust is recirculated. Petrol engines open the valve briefly and expect a rise in manifold pressure (GM 2004 V6, MIL on the first trip); older Ford systems measure the pressure drop across an orifice (DPFE sensor). Diesels balance the air mass: if the meter sees more fresh air than the target EGR rate allows, too little exhaust flows (GM, Ford, Saab, usually MIL after two trips). Diesel causes are mostly a coked valve or cooler, petrol causes blocked passages.
- What you may notice
- Check engine light on
- Pinging or knocking under load (petrol)
- Higher NOx, emission test failed
- Often no noticeable symptoms
- Likely causes
- LikelyEGR passages, valve or cooler carboned up
- LikelyEGR valve faulty or stuck closed
- PossibleFord: DPFE sensor or its hoses blocked, cracked or swapped
- PossibleDiesel: air mass meter drifting or air leak after the turbo
- RareVacuum control of the valve faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €100 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.