Mercedes-Benz ML 320 CDI
V6 diesel with common rail and piezo injectors. Powerful and refined. Known for blocked oil coolers, swirl flap failure and EGR problems. High mileages possible with good maintenance.
Diesel Sense
165 kW diesel in an SUV — sensible, economical and adequate. Driving fun is found elsewhere.
Engine Weaknesses 7
The best-known problem of the OM642: the oil cooler gaskets in the V-section of the engine fail. Oil leaks into the coolant or externally. Particularly prone on vehicles built up to 2009.
Symptoms: Oil loss warning, oil spots under the left side of the vehicle, oil streaks visible on the belt tensioner
The plastic linkages of the swirl flaps in the OM642 intake manifold break. Aluminium repair kits are available and more durable. In the event of complete failure there is a risk of debris entering the engine.
Symptoms: Engine warning light, fault codes for intake flap/swirl flap, power loss particularly at low rpm
Piezo injectors seal poorly from heat, diesel enters the engine oil. Oil loses lubrication properties, tar-like residue around injectors is the typical telltale sign.
Symptoms: Rough idle, increased fuel consumption, knocking noises, oil level rising due to diesel contamination, engine oil smells of diesel
Variable turbine geometry actuator linkage seizes due to soot deposits. Engine enters limp mode. Fault codes P0404, P2598, P2385. If runner damage occurs, turbo costs from €1,300.
Symptoms: Sudden power loss on kickdown, limp mode, black smoke, engine oil in intercooler area
The standard oil pump delivers insufficient pressure at high revs and temperatures. No warning in the cockpit. Connecting rod bearings wear unnoticed between 150,000–200,000 km, total engine failure looms.
Symptoms: Cold knocking at idle, metallic rattling during load changes, fine metal particles in oil filter, oil pressure drop only measurable late
With frequent short-trip driving the EGR system on the OM642 becomes heavily coked. Soot deposits in the intake manifold significantly reduce airflow.
Symptoms: Power loss particularly under load, poor throttle response, soot clouds, elevated fuel consumption
Thin-walled glow plugs corrode in the cylinder head and break during removal. Broken heating element requires time-consuming drilling out. Replace all 6 plugs preventively.
Symptoms: Difficult cold starting, extended pre-glow time required, glow indicator flashes, white smoke at cold start in winter
Vehicle Weaknesses 7
Water enters through defective tail light seals and damages the rear SAM module. Mainly pre-facelift models up to 2008 are affected.
Airmatic air struts develop leaks, particularly at certain ride height settings. The compressor pumps continuously and eventually burns out.
The 7G-Tronic transmission control unit develops faults at higher mileages. Gear engagement becomes impossible, limp mode activates.
Aluminium steering rack bolts corrode due to road salt. If all three bolts fracture, power steering fails completely. KBA recall 012425.
Pressure reservoir, compressor and air bags are highly vulnerable. Vehicle drops on one side or completely. Repair costs are very high due to expensive original parts and high labour rates.
Brake lines under the rear axle are prone to corrosion, particularly in high-salt regions. Line clips encourage moisture accumulation. Replacement requires lowering the rear axle.
The rear SAM fails when water enters through tail lights. Result: failure of lighting, wipers and displays. Mainly pre-facelift models up to 2008 affected.