P0400
- Powertrain
- Generic (SAE)
- Emissions
Diagnose soon
Usually safe to drive short distances, but the fault will not clear itself and can worsen or fail an emissions test.
Exhaust Gas Recirculation Flow Malfunction
This code is in our catalogue but has not yet been through editorial review, so the guidance below is limited to what our structured data supports. We publish deeper diagnostic content only after a code has been reviewed — here is why.
A general fault has been detected in the exhaust gas recirculation (EGR) system. EGR routes a portion of exhaust back into the intake to reduce combustion temperature and NOx emissions. Most EGR codes today are caused by carbon buildup blocking the valve.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Usually safe to drive short distances, but the fault will not clear itself and can worsen or fail an emissions test.
- Urgency
- Diagnose soon
- Will it pass emissions
- No
- Check engine light
- Solid
- Clearing the light
- A completed drive cycle is normally required before the monitor re-runs and the light can clear.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | EGR valve clogged with carbon | Very common | — |
| 2 | Intake EGR passages blocked | Common | — |
| 3 | DPFE / EGR position sensor failed | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
- EGR Valve
- EGR Cooler
- Dpfe Sensor
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Awaiting review
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