P0400 on Mercedes-Benz: How to Diagnose & Fix
Exhaust Gas Recirculation (EGR) Flow Malfunction
1 Mercedes-Benz model · 1 documented issue · $550-$1,900 repair
P0400 on Mercedes-Benz by model: symptoms, diagnosis and fix
Sprinter diesels (OM642 V6 and OM651 4-cylinder) recirculate soot-laden exhaust through the EGR valve and cooler. Over tens of thousands of miles the valve and the cooler's small passages choke with hard carbon, causing the valve to stick, EGR flow to read out of range, rough running, power loss and limp mode. Short-trip/urban duty cycles accelerate the buildup. The cooler is often more clogged than the valve and frequently cannot be cleaned, requiring replacement.
Common Symptoms
- Reduced power / limp mode
- Rough idle
- Check engine light
- Hesitation under load
- Failed emissions test
How to Fix
Scan for EGR codes, then clean or replace the EGR valve and inspect the EGR cooler. A clogged cooler usually must be replaced rather than cleaned. Clear adaptation/fault codes after the repair. Periodic highway driving and quality low-ash diesel oil help slow recurrence.
Sources for this issue (2)
P0400 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0400 mean on a Mercedes-Benz?
P0400 stands for "Exhaust Gas Recirculation (EGR) Flow Malfunction." P0400 is a generic powertrain code indicating the engine computer detected a problem with exhaust gas recirculation (EGR) flow — either too much, too little, or incorrect flow compared to what was commanded. The EGR system routes a small amount of exhaust back into the intake to lower combustion temperatures and reduce emissions. A fault can cause rough idle, pinging/knock, increased emissions, and failed emissions testing, though it is generally not an immediate driving hazard. On Mercedes-Benz it is documented across 1 model: Sprinter.
What are the most common causes of P0400?
The most common causes of P0400 are: Clogged or carbon-blocked EGR passages, Faulty EGR valve (stuck open or closed), Faulty EGR position or DPFE/flow sensor, Vacuum or electrical control fault to the EGR valve, Blocked or cracked EGR tube, Wiring/connector issues, PCM fault (rare). The specific cause varies by vehicle.
How much does it cost to fix P0400 on a Mercedes-Benz?
Published repair estimates on Mercedes-Benz range from $550 to $1,900 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0400 on a different make?
View P0400 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.