P0401 Exhaust gas recirculation (EGR) A flow insufficient
What P0401 means
The EGR system routes some exhaust gas back into the intake to lower combustion temperature and NOx emissions. P0401 means the engine computer commanded EGR flow but detected less than expected. Carbon build-up in the valve or passages is by far the most common reason.
P0401 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.
At a glance
- Severity
- Medium
- Typical repair cost
- 80–600 €
- Workshop time
- 1–5 h
- Repair difficulty
- Medium
- DIY possible
- Yes
- Check engine light
- Yes
- Affects emissions test
- Yes
Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.
Symptoms
- Check engine light on
- Pinging or knocking under load on petrol engines
- Usually no obvious change in driving
- Technical inspection failure for NOx
Common causes
- Carbon deposits blocking the EGR valve or passages
- EGR valve stuck closed or not opening fully
- Blocked EGR cooler (diesels)
- Faulty EGR vacuum solenoid or vacuum hose on vacuum-operated valves
- Faulty MAP or EGR position sensor reading the flow
Can I keep driving with P0401?
You can keep driving. Have the EGR system cleaned or repaired within about a week, particularly before a technical inspection.
What to check first
- Command the EGR valve with a scan tool and watch position and MAP or air-flow response
- Remove the EGR valve and inspect it and the intake passages for carbon
- Clean the valve and passages; on vacuum valves check the hoses and solenoid
- Replace the valve if it sticks or its position sensor is faulty after cleaning
Related codes
- P0400 Exhaust gas recirculation (EGR) A flow malfunction
- P0402 EGR flow excessive detected
- P0403 EGR A control circuit/open
- P0404 EGR A control circuit range/performance
- P0405 EGR sensor A circuit low
- P0406 EGR sensor A circuit high
- P0410 Secondary air injection system A
- P0411 Secondary air injection system incorrect flow detected
Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
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