Mercedes-Benz ML 270 CDI
Five-cylinder diesel with common rail. Unusual cylinder count, good balance of power and economy. Prone to blocked swirl flaps.
Diesel Duty
Only 120 kW diesel in an SUV. Adequate for daily use, not for excitement.
Engine Weaknesses 6
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.
The OM612 was delivered without a diesel particulate filter. EGR system, intake system and engine bay accumulate soot deposits over time.
Symptoms: Soot clouds on acceleration, visible soot deposits in engine bay, elevated particle readings at MOT
Vehicle Weaknesses 7
The US-built W163 received insufficient corrosion protection from the factory. Boot lid, sills, wheel arches and bonnet are particularly susceptible.
The wiring harness at the ABS hydraulic block chafes against the wheel arch liner and causes ABS and ETS failures. A known design fault.
Brake lines are known to corrode through. Complete replacement requires removal of the rear axle, driveshaft and fuel tank. A safety-critical problem.
The automatic transmission suffers premature torque converter wear, particularly on the ML 400 CDI and with frequent trailer use.
The transfer case chain stretches from around 100,000 km and can jump. Noises on pull-away are an early warning. In the worst case, total drivetrain failure.
Ladder frame rusts heavily, particularly at the rear and at longitudinal member sections. Suspension mounting points can be so weakened by corrosion that the vehicle's roadworthiness is at risk.
Cables in the tailgate transition break through constant opening and closing. Rear screen wiper, third brake light and number plate lighting are affected.