Trouble code
P0401
Exhaust Gas Recirculation Flow Insufficient
What P0401 means
The EGR system is not flowing the exhaust gas the computer commanded, usually because the passages are carboned up.
Symptoms you may notice
- Pinging under load
- Rough idle
- Failed emissions test
Common causes, cheapest first
- Carbon blocked EGR passages
- Stuck EGR valve
- Failed EGR position sensor or solenoid
- Blocked EGR cooler on diesels
Before you buy anythingClean the passages before replacing the valve. On many engines the ports clog solid with carbon and a new valve bolted onto a blocked passage sets the same code within a week.
What to do next
- Confirm the code with your own scan tool, or have it read free at a chain parts store.
- Decode your VIN so you know your exact engine and build date.
- Work down the causes above from cheapest to most expensive.
- Search NHTSA for a recall or service bulletin covering this symptom on your vehicle.
- Read the engine buying guide before ordering.
P0401 is a generic OBD-II code, standardized across every make and model sold in the US from 1996 onward. The meaning is the same on any vehicle; the specific part and its location are not.
Parts
Parts commonly needed for P0401
These go to Amazon. We earn a commission if you buy, at no extra cost to you — see our affiliate disclosure. Which one you actually need depends on diagnosis — read the note above first.
Confirm fitment against your VIN on the listing page before ordering. A part that matches your year and model can still be wrong for your build date or engine code.