P0401 exhaust gas recirculation flow insufficient detected
P0401 tends to return a few days after it's cleared, because whatever is restricting the EGR flow hasn't gone anywhere. We read the live EGR data at your home, yard or depot and tell you what will stop it coming back.
Why P0401 comes back after clearing
Clearing the code switches the light off and wipes the stored record, but the valve, pipes and cooler stay as they were. The ECU reruns its EGR flow test once the engine is warm and the vehicle is at a steady speed.
If the flow is still short, the test fails and P0401 is logged again, sometimes the same day. A van can flick between light on and light off for weeks this way without the fault getting any closer to a fix.
The usual causes behind P0401
| Cause | How it's checked |
|---|---|
| Carbon build-up in the EGR valve | Commanded valve position compared with actual position on live data |
| Blocked EGR passages or intake | Flow readings, plus a look inside where access allows |
| Blocked or failing EGR cooler | Cooler codes such as P2457, temperature readings and any coolant loss |
| Faulty EGR position sensor or air flow sensor | Sensor figures compared with what the engine is actually doing |
| Wiring or connector fault at the valve | Circuit checks and related codes such as P0403 |
| Split vacuum pipe or faulty solenoid on vacuum-operated valves | Vacuum test |
Symptoms
- The engine management light returning days after it was cleared
- Often no obvious change in power, which is why the code gets cleared and forgotten
- A lumpy idle or hesitation where carbon makes the valve stick now and then
- A harsher diesel knock at light throttle, as combustion runs hotter with less exhaust gas fed back
- Coolant going down or white smoke, if a failing EGR cooler is part of the problem
Using the vehicle with P0401 showing
Most vehicles keep going with P0401 stored and feel no different at first. Some may limit power if it repeats, the lit light is an MOT fail and carbon keeps building. If coolant is dropping too, get it checked before going further.
Vans and fleets with P0401
Stop-start routes are hard on EGR valves, as the engine rarely gets hot enough to keep carbon at bay. We come to your yard or depot and check vans between jobs, so none comes off the road for a garage to find the fault.
Businesses with regular work for us can open a trade account. Details are on our trade and partners page.
How we stop P0401 coming back
Live EGR diagnosis, £100 + VAT
We compare the valve's commanded and actual position and the change in airflow, which tells a sticking valve apart from a blocked cooler or a sensor fault. You get a clear diagnosis to hand to your garage.
Valve or cooler replacement
A garage replaces whichever valve or cooler is at fault. Our EGR valve replacement cost guide covers what to expect.
EGR delete, £220 + VAT
A software delete stops the ECU running its EGR flow test, so P0401 has nothing to report.
Reviews
Why does P0401 come back after it's been cleared?
Clearing only removes the record. The restriction is still in the valve, pipes or cooler, so the next failed flow test logs the code again.
Can a remap cause P0401?
A badly written map that changes airflow targets without allowing for the EGR system can upset the flow test. A well set-up remap keeps within safe limits and leaves the EGR system doing its job.
Can another fault set off P0401?
Yes. A failing air flow sensor, perhaps logging P0101, a boost leak or a split intake pipe can all throw out the ECU's flow calculation, so the EGR valve takes the blame.
Can you check P0401 on our vans at the depot?
Yes. We work at yards and depots across Greater Manchester, Lancashire, Merseyside, Cheshire and Huddersfield. Tell us how many vans are showing the code when you book.
What should I tell you when I book for P0401?
The registration, the full code including any extra digits, how often it has come back and any other warnings. Mention coolant loss too, as that points towards the EGR cooler.
What does P2457 mean?
P2457 is the code for EGR cooling system performance. The cooler isn't bringing the exhaust gas temperature down as expected, often because it's blocked with soot or leaking, and it can turn up alongside P0401. Our EGR cooler failure guide covers the signs.
Can an EGR delete be done on a vehicle used on the road?
No. We only carry out EGR deletes on vehicles used off-road or for export, as Is EGR delete legal? explains.
Stop P0401 coming back
Book a fault check and we'll find what's restricting the EGR flow, at home, at work or at the depot between jobs.
More fault codes explained
Eccles, Manchester M30 0SF