OBD2 code P0400: EGR A Flow
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 under load or rough idle, depending on direction
- Higher NOx, emission test failed
Possible Causes
- EGR passages or valve carboned up
- EGR valve stiff or faulty
- Leak in the intake or EGR pipe
- MAP or MAF sensor inaccurate
Tools Required
Interactive Diagnostic
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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 P0400
What does code P0400 mean? ▾
OBD2 code P0400: EGR A Flow. 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 P0400? ▾
Code P0400 may cause: Check engine light on, Pinging under load or rough idle, depending on direction, Higher NOx, emission test failed. The intensity of these symptoms varies depending on the vehicle and driving conditions.
What causes code P0400? ▾
The most common causes of code P0400 are: EGR passages or valve carboned up, EGR valve stiff or faulty, Leak in the intake or EGR pipe, MAP or MAF sensor inaccurate. A proper OBD2 diagnostic will pinpoint the exact cause.
Is it serious to drive with code P0400? ▾
Code P0400 has moderate severity (Warning). Short-term driving remains possible, but a prompt check is recommended to prevent worsening.
How do I fix code P0400? ▾
Start by reading the code with an OBD2 scanner, then follow the interactive decision tree on this page. Priority causes to check: EGR passages or valve carboned up, EGR valve stiff or faulty, Leak in the intake or EGR pipe, MAP or MAF sensor inaccurate. Difficulty: Medium · Estimated time: 30-60min.