Mercedes-Benz E 270 CDI

The most notorious problem in the OM612/OM646 CDI family: failing injector sealing rings allow combustion gases to escape. A black, tar-like mass forms around the injectors.

Symptoms: Black tar visible around injectors, hissing or knocking under load, diesel smell in interior

The EGR cooler on the OM612 can develop internal leaks and introduce coolant into the intake. This leads to white smoke, coolant loss and in the worst case hydro-lock.

Symptoms: White smoke from exhaust, coolant loss, sweet smell from exhaust, coolant in air filter housing

Cylinder head cracks can form in the OM612 between two valves, only becoming visible under load.

Symptoms: Coolant loss without visible leak, white smoke, bubbling in coolant reservoir under load.

The variable turbine geometry on the single turbocharger can suffer vane breakage. Metal fragments enter the engine; catastrophic secondary damage is possible.

Symptoms: Turbo noise changes character, power loss, oil smoke, engine warning light

In the OM612, swirl flap shafts and actuating levers break due to oil carbon deposits. Complete intake manifold replacement required.

Symptoms: Power loss under rapid acceleration, soot clouds, engine limp mode, swirl flap fault codes.

Bacterial contamination in the electrophoretic coating bath compromised paint adhesion. Rust appears on doors, roof, boot lid and trim strips. Mercedes offered goodwill repairs.

Strut towers corrode severely and can break away from the bodywork. Safety-critical defect: the vehicle can drop uncontrollably.

Wheel arches, sills and strut towers rust heavily. Hidden rust forms beneath the sill cladding.

Front and rear strut towers rust through. At the front the towers can break while driving. At the rear this is an economic write-off.

Electronic ignition lock wears out over time. Key turns but vehicle won't start. Problems worsen in cold weather.