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Exhaust Gas Recirculation Flow Insufficient Detected
🟡 SERVICE SOON POWERTRAIN · EGR System
EGR monitor detected exhaust gas flow is below expected rate during commanded EGR on test.
What You'll Notice
- Engine ping / knock at light throttle on acceleration
- Rough cold start in some configurations
- MIL on
Probable Causes
- Clogged EGR passages — carbon buildup blocking flow port in intake manifold
- Faulty EGR valve (stuck closed or diaphragm failure on vacuum-operated type)
- DPFE sensor failure (Ford-specific — differential pressure sensor)
- Clogged EGR cooler (diesel engines)
Direct Repair Steps
- Remove EGR valve; inspect and clean passages with EGR cleaner and a wire brush
- Test EGR valve operation: vacuum-type — apply 15 inHg, idle should drop; electronic — command with scan tool
- Ford DPFE sensor: inspect hoses for cracks, test sensor output voltage (0.5 V key-on, rises with EGR flow)
- Replace EGR valve if stuck or diaphragm is perforated ($25–120 DIY)
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Check PriceQuick answers
What does P0401 mean?
EGR monitor detected exhaust gas flow is below expected rate during commanded EGR on test.
Is P0401 serious?
It depends on the system and symptoms, but the page ranks the severity and likely causes so you can decide whether to stop driving or continue with caution.
What should I buy before troubleshooting P0401?
A reliable OBD2 scanner helps confirm the code, read live data, and avoid guessing before repairs.