OBD2 code P0401: EGR A Flow Insufficient Detected
Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx.
Detected Root Component
EGR Valve
Technical Component Diagrams
EGR Valve Layout
Diag Expert technical diagram
EGR Valve Connector
Diag Expert technical diagram
Observed Symptoms
- Check engine light on
- Pinging or knocking under load (petrol)
- Higher NOx, emission test failed
- Often no noticeable symptoms
Possible Causes
- EGR passages, valve or cooler carboned up
- EGR valve faulty or stuck closed
- Ford: DPFE sensor or its hoses blocked, cracked or swapped
- Diesel: air mass meter drifting or air leak after the turbo
- Vacuum control of the valve faulty
Tools Required
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Parts likely to be the cause (Vanne EGR)
Vanne EGR
Photo d'illustration : Vanne EGR
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Frequently asked questions about code P0401
What does code P0401 mean? ▾
OBD2 code P0401: EGR A Flow Insufficient Detected. Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx.
What are the symptoms of code P0401? ▾
Code P0401 may cause: Check engine light on, Pinging or knocking under load (petrol), Higher NOx, emission test failed, Often no noticeable symptoms. The intensity of these symptoms varies depending on the vehicle and driving conditions.
What causes code P0401? ▾
The most common causes of code P0401 are: EGR passages, valve or cooler carboned up, EGR valve faulty or stuck closed, Ford: DPFE sensor or its hoses blocked, cracked or swapped, Diesel: air mass meter drifting or air leak after the turbo. A proper OBD2 diagnostic will pinpoint the exact cause.
Is it serious to drive with code P0401? ▾
Code P0401 has moderate severity (Warning). Short-term driving remains possible, but a prompt check is recommended to prevent worsening.
How do I fix code P0401? ▾
Start by reading the code with an OBD2 scanner, then follow the interactive decision tree on this page. Priority causes to check: EGR passages, valve or cooler carboned up, EGR valve faulty or stuck closed, Ford: DPFE sensor or its hoses blocked, cracked or swapped, Diesel: air mass meter drifting or air leak after the turbo. Difficulty: Medium · Estimated time: 45-90min.