Engine and gearbox (P)
P0401: EGR Flow Insufficient
The exhaust gas recirculation (EGR) system is not allowing enough exhaust gases to flow back into the intake manifold. This can affect emissions and engine performance.
Checked by a licensed car technician · last reviewed 29 September 2026
Symptoms
- Check engine light on
- Rough idle
- Reduced fuel efficiency
- Increased emissions
Common causes
- Carbon blockage in EGR passages
- Stuck EGR valve
- Failed EGR position sensor
- Faulty EGR solenoid
- Vacuum leak
How to check it yourself
- Inspect EGR valve for movement
- Check for carbon buildup in EGR passages
- Test EGR position sensor
- Inspect vacuum lines for leaks
- Verify EGR solenoid operation
Can I keep driving?
The car can still be driven, but it may run less efficiently and produce higher emissions.
General guidance, not a professional inspection. Confirm faults with measurements before buying parts, and use a qualified mechanic for brakes, steering, fuel leaks, airbags, and other safety-critical work. Terms and disclaimer