What does P0400 mean?
The exhaust gas recirculation (EGR) system feeds a small amount of exhaust back into the intake. That lowers combustion temperatures and cuts NOx emissions. This code means the computer found a problem with EGR flow or control.
The part is electrically connected, but it is not doing what the computer commanded.
Codes are a starting point. They tell you which test failed, not which part to replace. Check for other stored codes and fix those in a sensible order.
Symptoms
- Check engine light
- Pinging under load (insufficient flow)
- Rough idle or stalling (excessive flow or stuck-open valve)
- Failed emissions test
Common causes
- Sticking or worn component
- Restricted passage or linkage
- Wiring with high resistance
- Low battery or charging voltage
- Carbon buildup in the EGR valve or passages
- Failed EGR valve
- Faulty EGR position or pressure sensor (DPFE on older Fords)
How to diagnose P0400
- Command the component with a scan tool and watch whether it responds.
- Check the component's actual movement or flow.
- Inspect wiring and voltage supply.
- Command the EGR valve with a scan tool and watch the position feedback.
- Check passages for carbon buildup.
How to fix it
- Clean the EGR valve and passages
- Replace the EGR valve
- Replace the EGR sensor
- Repair vacuum lines or wiring
Estimated repair cost
Likely repairs for P0400 run from about $150 to $1,500, depending on the cause.
| Repair | Typical range (parts + labor) |
|---|---|
| Diagnostic fee (scan + testing) | $100 - $200 |
| EGR valve/passage cleaning | $150 - $600 |
| EGR valve replacement (gasoline) | $250 - $700 |
| EGR valve replacement (diesel) | $400 - $1,500 |
These are rough US estimates for an independent shop in 2026, based on typical parts prices and standard labor times. Dealers, big trucks, luxury brands and high-cost areas often run higher. They are not quotes. Use the repair cost estimator to adjust for your vehicle.
How serious is P0400?
Moderate severity
Usually drivable. Fix it to avoid pinging and failed emissions tests.
P0400 FAQ
What does P0400 mean?
P0400 stands for "Exhaust Gas Recirculation Flow". The exhaust gas recirculation (EGR) system feeds a small amount of exhaust back into the intake.
Can I drive with a P0400 code?
Usually drivable. Fix it to avoid pinging and failed emissions tests.
How much does it cost to fix P0400?
It depends on the cause. The likely repairs for P0400 range from about $150 to $1,500 at an independent shop in the US, plus a diagnostic fee of roughly $100-$200. These are rough estimates; dealer prices and some vehicles run higher.
What is the most common cause of P0400?
The most common causes are: sticking or worn component; restricted passage or linkage; wiring with high resistance.