P0401
EGR A Flow Insufficient Detected
Exhaust gas recirculation
Generic OBD-II
Medium
What it means
P0401 means the engine control module commanded exhaust gas recirculation but measured less flow than expected. The EGR system routes a little exhaust back into the intake to lower combustion temperatures and emissions; when flow is too low, usually from carbon buildup, the car still drives but runs hotter in the cylinders and will fail an emissions test.
Medium
Can I keep driving? Yes, you can keep driving — the car runs normally, but expect possible light pinging and a failed emissions test until it's fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Light knock or pinging under load (higher combustion temperatures)
- Slightly rough idle or minor hesitation
- Will fail an emissions/smog test
Common causes
Most likely first
- Carbon-clogged EGR passages or ports (the most common cause)Likely
- EGR valve stuck closed or not opening fullyCommon
- Faulty EGR temperature or position sensor giving a false low-flow readingCommon
- Wiring or connector fault in the EGR circuitLess often
- Failed engine control module (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data, then remove the EGR valve and inspect the valve and passages for carbon buildup.
- Clean the clogged EGR ports and valve; this resolves many P0401s without new parts.
- Test the EGR valve operation and replace it if it won't open or seal.
- Check the EGR temperature/position sensor and its wiring for correct signal.
- Clear the code and drive a full cycle to confirm the flow monitor passes.
FAQ
Quick answers
Is it safe to drive with P0401?+
Yes, short-term. The engine runs, but insufficient EGR raises combustion temperatures and can cause pinging, so fix it before long trips or towing.
Can I just clear P0401?+
It will come back within a drive cycle or two unless the clogged passages or valve are actually cleaned or repaired.
Related codes
Often seen with P0401
Read & clear P0401 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX