P0401 on a Mercedes-Benz: Causes, Fixes & Repair Cost
🟠 Moderate severity · drivable
Safe to drive short term, but on a diesel the sooty EGR valve can eventually cause limp mode, so plan the repair soon.
What P0401 means on a Mercedes-Benz
On a Mercedes-Benz, P0401 means the engine computer detected too little exhaust gas flowing through the EGR system. On Mercedes this code mostly shows up on CDI diesel engines, where soot clogs the EGR valve and the EGR cooler and reduces flow.
Is P0401 common on Mercedes-Benzs?
P0401 is common on Mercedes diesel models like the E-Class, ML-Class, and Sprinter with CDI engines. The EGR valve and cooler clog with soot over time; gasoline Mercedes models rarely trigger this code.
Commonly reported on: C-Class, E-Class, ML-Class, Sprinter.
Symptoms
- Check engine light is on
- Rough idle or hesitation
- Reduced fuel economy on a diesel
- Possible limp mode on heavy EGR failure
Common causes
- most common: EGR valve caked with soot
- common: Clogged EGR cooler
- common: Carbon buildup in the EGR intake passages
- less common: Faulty EGR position sensor
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Remove and clean the EGR valve | Yes | $50–150 |
| Replace the EGR valve | Mechanic | $300–700 |
| Replace or flush the clogged EGR cooler | Mechanic | $500–1200 |
Frequently asked questions
Other common Mercedes-Benz codes
P0401 on other brands
Looking for the full (non-brand-specific) guide? See the P0401 code page →
Browse all Mercedes-Benz codes: Mercedes-Benz hub →
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.