OM646 2.1 CDI
The four-cylinder diesel that carried the W211, and a durable one. Bottom ends go a very long way, so the money is in the injectors and the emissions hardware. The later 170 PS version is the one worth finding.
| Configuration | I4, turbocharged | Displacement | 2148 cc |
| Fuel | diesel | Injection | common rail |
| Shared components | DPF · EGR cooler | ||
Cars using this engine
Engine and component issues
Warning light, limp mode, oil level rising above the maximum mark from fuel dilution. The filter needs sustained hot running to regenerate. A car used for short urban trips never completes a regeneration cycle.
Check: Read the DPF soot load and the distance since the last regeneration on a scan tool, and check the engine oil level and smell it for diesel. Ask what the car was used for. A short-trip city diesel is the wrong car regardless of mileage.
A chuffing noise from the engine bay, a diesel smell in the cabin, and black carbon deposits building up around the injector. 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.
Check: Look for black tarry deposits around the injectors with the cover off, and listen for a rhythmic chuffing at idle.
Coolant loss with no visible external leak, white smoke, sweet smell. The EGR cooler cracks internally and leaks coolant into the intake. BMW recalled affected diesels over a fire risk from glycol deposits igniting.
Check: Check coolant level and look for unexplained top-ups in the service history. Verify the recall was carried out. It's free and searchable by VIN.
Chassis, gearbox and body issues aren't listed here. They depend on which car the engine is fitted to. Open a variant page for the merged list.