P0400 to P0402: exhaust gas recirculation flow
The engine computer measured less exhaust gas recirculation than it asked for (P0401), or more (P0402). P0400 is the general flow fault.
SeverityModerateUsually not urgent today, but it can get worse if left.
Can you keep driving?Drive gently, check it soonWhat does P0401 mean?
The EGR valve feeds a little exhaust gas back into the intake to lower the combustion temperature and NOx emissions. The computer opens the valve and looks for the expected change in manifold pressure, in the mixture or on a dedicated sensor. Too little flow usually means carbon has narrowed the passages; too much means the valve is not closing.
What causes P0401?
- Carbon build-up in the EGR valve or its passages, very common on diesels and direct-injection petrol engines
- An EGR valve that sticks open or closed
- A faulty position sensor, or a vacuum supply problem on vacuum-operated valves
- A blocked EGR cooler on engines that have one
What to check first for P0401
- Compare the commanded and actual EGR position on a scan tool
- Inspect the valve and its passages for carbon
- Check the vacuum lines or the electrical connector, depending on the type of valve
- Ask whether the manufacturer has a software update for this fault
Can you drive with P0401?
Usually safe to drive to a workshop. Too little flow raises NOx and can cause knocking; a valve stuck open can make the engine idle roughly or stall, and in that case keep the trip short.
Since May 2018 an engine warning light that stays on is a major defect at the MOT, so the car fails until the fault is fixed.
Codes on this page
- P0400Exhaust Gas Recirculation Flow
- P0401Exhaust Gas Recirculation Flow Insufficient Detected
- P0402Exhaust Gas Recirculation Flow Excessive Detected
Related codes
Checked on · Rafael Soares
These are the generic meanings every manufacturer shares. Each brand adds its own detail, so your car's handbook, its service information and a qualified mechanic have the last word. OdoKeep has no connection with any manufacturer, and the app does not read codes from the car.
