P0401 Fault Code on Mercedes C-Class — UK Guide (2007–2021)

P0401 on the Mercedes C-Class — what you need to know

Mercedes C-Class diesel P0401 EGR fault is common on the CDI engines. Mercedes EGR valves are expensive — always attempt cleaning before replacement. An EGR blanking plate is sometimes used but affects emissions compliance.

The affected engine variants are: C200 CDI, C220 CDI, C250 CDI. If your Mercedes C-Class is showing fault code P0401, use our AI Diagnostic Report for a full UK-specific analysis including the exact repair costs for your engine and year.

Common causes on the Mercedes C-Class

While P0401 can have several root causes, the most common reasons this code appears on the Mercedes C-Class in UK conditions are related to the specific engine management and emissions systems fitted to this vehicle. Always scan for related fault codes before replacing any parts — a secondary code can point directly to the root cause and save hundreds of pounds.

For the complete diagnosis guide including step-by-step testing procedures, see our main P0401 fault code page.

UK repair costs for P0401 on the Mercedes C-Class

Typical UK repair costs for P0401 on the Mercedes C-Class range from £50 to £400 depending on the exact cause, your engine variant and whether you use an independent garage or a main dealer. Independent garages are typically 30–50% cheaper than franchised dealers for this type of repair.

Always get at least two quotes. Use our AI Diagnostic Report to understand the most likely cause for your specific Mercedes C-Class before spending anything at a garage.

P0401 MOT implications for the Mercedes C-Class

An active P0401 fault code on your Mercedes C-Class is likely to cause an MOT failure. Under DVSA testing standards, an illuminated check engine light is an automatic MOT failure regardless of how the vehicle drives. You must resolve this fault before your MOT test. Read our full MOT guide for more information.