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.
Scan your own car in about 60 seconds: see whether P0400 is really what it has, how urgent it is, and what the fix should cost. Free on iPhone and Android, on any ELM327 adapter.
Get Skanyx freeP0400 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.
P0400 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0400 and illuminates the check engine light.
If your vehicle has triggered P0400, you may notice one or more of these symptoms:
Here are the most common causes of P0400:
Generally yes, for short-term driving. The vehicle is generally safe to drive in the short term, but EGR faults can cause increased NOx emissions, rough idle, and reduced fuel economy. Repair before the next emissions inspection.
Follow these steps to pinpoint the root cause of P0400:
Repair costs for P0400 vary depending on the root cause and your vehicle. Here are typical estimates:
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Full repair guides
Engines known for this code
P0400 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:
The 1.9 TDI and 2.0 TDI engines are well-known for EGR valve carbon clogging, especially in stop-and-go city driving. The EGR cooler on the 2.0 TDI (CR) can also crack, leading to coolant loss. Regular motorway driving helps keep the EGR cleaner.
The 1.7 CDTi (Z17DTH/A17DTJ) is very susceptible to EGR clogging, particularly in urban driving. The EGR valve on these engines is electrically operated and can seize in the open position, causing rough idle and excessive smoke.
The 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.
These codes are often seen alongside P0400 or indicate related issues:
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.
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.
Diesel engines soot the EGR up far faster than petrol engines, so a diesel reaches the point of needing a clean much sooner. How quickly depends on how the car is driven: short trips and stop-start use load it fastest.
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.
No. Blocking or deleting the EGR system breaks the emissions type approval the car was registered under, which is why it is prohibited across the EU, and an inspector who finds it has grounds to reject the vehicle, with the checks and the penalties set by each country. It also significantly increases NOx emissions. The correct approach is to clean or replace the faulty component.
A 15 euro Bluetooth adapter and a free phone app read the exact fault code a shop charges 30 to 100 euros to pull. Here is how to do it yourself in 5 minutes.
Fixing P0401 starts with cleaning the EGR valve, under 20 euros if you do it yourself. Replacement runs 160-550 euros. Here is how to know which one you need.
A bad EGR valve causes rough idle, hesitation, and a P0401 code. Here is what the valve does, the symptoms of stuck open vs stuck closed, and the repair cost.
A flashing check engine light means the engine is misfiring right now. Pull over and read the code: the fix is usually $80 to $400, the delay costs $1,500 up.
An unfamiliar symbol just lit up and you need to know whether to stop. Read the colour first, then find your symbol in the table: every one carries its verdict.
Your car logged P0400. Skanyx reads it on any standard Bluetooth OBD2 adapter, tells you whether it is safe to keep driving, and shows the €50-€1400 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.
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