Injector seat leaks and seized injectors
Attaches to OM646 at engine level · Fuel · carried by 2 variants across 2 chassis
Overview
Injector seat leaks and seized injectors is a common fault recorded against OM646 at engine level, typically from 150–280k km. It shows up as a chuffing noise from the engine bay, a diesel smell in the cabin, and black carbon deposits building up around the injector. Where it's documented, the repair runs €400–€1,200 (seals and injector removal at a specialist, more if one seizes, costs dated 2026-07), and it can be checked before you buy. 2 variants across 2 chassis in this database inherit it.
What happens
Symptom. A chuffing noise from the engine bay, a diesel smell in the cabin, and black carbon deposits building up around the injector.
Cause. The copper seat washer fails and combustion gases leak past the injector, carbonising the seat. Left alone the injector can seize in the head, and extraction then becomes the expensive part of the job.
How to check it
Static checks
Look for black tarry deposits around the injectors with the cover off, and listen for a rhythmic chuffing at idle.
Engine off, ideally on a lift.
Every variant that carries this
| Variant | Chassis | Body | Years | Risk | Good buy | Cost as % of good buy |
|---|---|---|---|---|---|---|
| E 220 CDI OM646 | W211 | sedan | 2002–2009 | R3 | €3,150 | 25% |
| E 220 CDI OM646 | S211 | wagon | 2003–2009 | R3 | €3,350 | 24% |
The last column is the point. The same repair is an inconvenience on one variant and a reason to scrap the car on another. A failure costing a quarter of the vehicle's value changes the purchase decision regardless of how rare it is.