P0401moderate severityPowertrain
EGR Flow Insufficient Detected
on 2010 BMW M3 E90 4.0L V8 S65 · RWD
What this code means
The EGR system is not flowing enough exhaust gas. This is one of the most common EGR codes.
Symptoms
- Check Engine Light
- Pinging under load
- Failed emissions (high NOx)
- Slight rough idle
Common causes
- Clogged EGR passages (most common)
- EGR valve stuck closed
- Clogged EGR tube
- Faulty DPFE/MAP sensor
- Carbon buildup in intake manifold
Diagnostic steps
- Check EGR passages for carbon restriction
- Test EGR valve by applying vacuum (should open and idle should change)
- Inspect EGR tube between exhaust and valve
- Test DPFE sensor (Ford) or EGR position sensor
- Clean carbon from intake ports
Repair notes
Clean EGR passages and valve. This is maintenance, not just a repair. Replace EGR valve if cleaning fails.
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Other Powertrain codes on this vehicle
29CC
Misfire Cylinder 1
29CD
Misfire Cylinder 2
29CE
Misfire Cylinder 3
29CF
Misfire Cylinder 4
29D0
Misfire Cylinder 5
29D1
Misfire Cylinder 6
29D2
Misfire Cylinder 7
29E0
Lambda Additive/Idle Adaptation Limit, Bank 1
29E1
Lambda Additive/Idle Adaptation Limit, Bank 2
29E2
Lambda Multiplicative Part-Load Adaptation Limit, Bank 1