P0401
PowertrainEmission Controlsmoderate severityEGR Flow Insufficient Detected
What P0401 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
Where to start: Clean EGR passages and valve. This is maintenance, not just a repair. Replace EGR valve if cleaning fails.
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