P0400 means the engine control unit has detected that exhaust gas recirculation flow is not within the expected range. The EGR system recirculates a portion of exhaust gas back into the intake to lower combustion temperatures and reduce NOx emissions. A blockage or valve failure disrupts this flow.
DTC/P0400·Peugeot
P0400 on Peugeot: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Peugeot
P0400 on a Peugeot means the engine control unit has detected that exhaust gas recirculation flow is not within the expected range. The EGR system recirculates a portion of exhaust gas back into the intake to lower combustion temperatures and reduce NOx emissions. A blockage or valve failure disrupts this flow.
Repair cost on Peugeot€53 - €945
What does P0400 mean on a Peugeot?
Peugeot 308
2007-2024The 1.6 HDi (DV6) engine shares its EGR system with the Ford 1.6 TDCi and is equally prone to carbon clogging. The 2.0 HDi has a more robust EGR setup but the cooler can develop leaks after 100,000 km.
What causes P0400 on a Peugeot?
Beyond the generic causes listed on the main P0400 page, these are the Peugeot-specific patterns we see most often:
Peugeot 308Carbon clogging on 1.6 HDi EGR valve
Peugeot 308EGR cooler leak on 2.0 HDi after high mileage
How to diagnose P0400 on a Peugeot with OBD2
Follow these steps to pinpoint the root cause of P0400:
- Check for companion EGR codes (P0401, P0402, P0403) that may help narrow down whether the issue is insufficient flow, excessive flow, or an electrical fault
- Remove the EGR valve and visually inspect for carbon buildup. A heavily clogged valve is the most common cause and can be cleaned with carburettor cleaner
- With the EGR valve removed, inspect the intake and exhaust passages for carbon blockage. Use a flashlight and probe to check passage diameter
- Test the EGR valve operation by applying vacuum (vacuum-operated) or commanding it open with a scan tool (electronic). It should open and close smoothly
- If the valve operates correctly, check the DPFE sensor or EGR position sensor readings on the scan tool against manufacturer specifications
How much does P0400 cost to fix on a Peugeot? (EUR)
Estimated repair costs on a Peugeot (Peugeot parts and labour typically run 5% above the average for this code).
Prices estimated as of May 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0400 on Peugeot
These codes commonly cluster with P0400 on Peugeot vehicles:
FAQ: P0400 on Peugeot
What does the EGR system do?
The Exhaust Gas Recirculation system routes a small amount of exhaust gas back into the engine intake. This lowers combustion temperatures and significantly reduces nitrogen oxide (NOx) emissions, which are a major component of smog.
Can I drive with P0400?
Yes, for a short time. The vehicle will run, but you may notice rough idle, knocking under load, and poor fuel economy. The main risk is failing an emissions test and potentially causing increased engine wear from higher combustion temperatures.
How often does the EGR valve need cleaning?
On diesel engines, EGR cleaning every 40,000 to 60,000 km is advisable due to higher soot levels. Petrol engines accumulate carbon more slowly, but a cleaning every 80,000 to 100,000 km is good preventive maintenance.
What is the difference between P0400 and P0401?
P0400 is a general EGR flow malfunction, meaning the flow is outside the expected range. P0401 specifically means insufficient EGR flow, which is usually caused by a clogged valve or blocked passage. P0400 is less specific about the direction of the fault.
Is it OK to delete or block the EGR valve?
In the EU, blocking or deleting the EGR system is illegal and will cause the vehicle to fail its periodic roadworthiness test (TUV, MOT, ITV, etc.). It also significantly increases NOx emissions. The correct approach is to clean or replace the faulty component.
Looking for the full P0400 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0400 guideSkanyx · Peugeot
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