Error code P0400 is displayed and the check engine light is on - what does this mean?
The OBD/EOBD system has detected a fault in the exhaust gas recirculation system (EGR system). This DTC P0400 indicates insufficient or blocked exhaust gas recirculation, which can occur with various manufacturers such as Volkswagen, BMW, Mercedes-Benz and others.
What causes can this error code have?
- Blocked or defective EGR valve
- Blocked EGR lines due to soot deposits
- Defective EGR position sensor
- Damaged vacuum lines to the EGR system
- Faulty electrical connections on the EGR valve
- Defective control unit software
- Clogged EGR cooler
- Loose or corroded plug connections
What symptoms occur in parallel with fault code P0400?
- Increased emission values: Poor emission values during the main inspection
- Uneven idling: Engine runs unevenly at idle speed
- Loss of power: Reduced engine power, especially at low engine speeds
- Knocking noises: Combustion noises due to increased combustion temperatures
- Increased fuel consumption: Poorer engine efficiency
- Black smoke: Visible soot particles in the exhaust gas
How to fix the problem of trouble code P0400?
- Repairing trouble code P0400 requires a systematic approach to restore proper EGR function.
- Remove the EGR valve, clean thoroughly or replace completely if defective (costs: 150-400 euros)
- Remove soot deposits from the EGR lines and ducts using a special cleaner
- Check EGR position sensor and replace if malfunctioning (costs: 80-200 euros)
- Check all vacuum lines for cracks and leaks and replace defective hoses
- Check electrical connections on the EGR system, clean and replace if corroded
- Clean or replace EGR cooler professionally if blocked (costs: 200-500 euros)
- Update control unit software or have adaptation values reset after repair
FAQ - Frequently asked questions about DTC P0400
Can I continue driving with error code P0400?
It is possible to continue driving for a short time, but the fault code should be rectified as soon as possible. The defective EGR system leads to increased emissions and can damage the engine in the long term.
How much does it cost to repair fault code P0400?
The repair costs vary between 100-600 euros, depending on the cause. A simple EGR valve cleaning costs around 100-150 euros, while a complete valve replacement can cost 300-400 euros.
How often does the code P0400 occur?
The EOBD fault code P0400 is one of the more common exhaust faults, especially in diesel vehicles with high mileage. Regular maintenance can reduce its occurrence.
Can I repair the P0400 myself?
Basic cleaning work on the EGR valve is possible for experienced hobby mechanics. However, more complex repairs should be left to a specialist workshop.
How long does it take to repair the P0400?
Depending on the complexity, it takes between 1-4 hours to repair OBD code P0400. A simple cleaning can be completed in 1-2 hours, a valve replacement can take longer.
Does P0400 prevent TÜV approval?
Yes, the active error code P0400 leads to a refusal of the MOT, as it impairs the exhaust gas purification. The code must be rectified before the main inspection.