Mercedes-Benz OM642 engine (2005-on)

Available from 2005, the Mercedes-Benz OM642 was a 3.0-litre V6 turbo-diesel engine which replaced the five- and six-cylinder OM647 and OM648 engines.

Manufactured in Marienfelde, Berlin, and Stuttgart-Untertürkheim, the 2987 cc OM642 engine had 83.0 mm bores, a 92.0 mm stroke, a 72-degree ‘V’ angle, an aluminium block and cylinder head, common-rail direct injection (operating at up to 1600 bar) with piezo injectors each with eight injection nozzles, a variable geometry turbocharger (VGT or variable nozzle turbine, VNT), double overhead camshafts (duplex chain driven), compression ratio of 18.0:1 and a diesel particulate filter. Furthermore, the OM642 engine had a counter-rotating balance shaft between the cylinder banks.

In early 2014, Mercedes-Benz’s ‘Nanoslide’ cylinder wall coating was introduced for the OM642 BlueTEC turbo-diesel engine for greater fuel efficiency and mass reduction.

OM642 Engine Problems

Knocking or ticking noise at idle – crankshaft main bearing

In February 2013, Mercedes-Benz issued Service Bulletin LI03.20-P-048278 for Mercedes-Benz models that had OM642 diesel engines. According to LI03.20-P-048278, these vehicles may exhibit an intermittent knocking, ticking or knocking noise at idle and at engine speeds up to 1500 rpm. Specifically,

• The noise would occur after a mileage of approximately 32,000 kilometres or after an oil change;
• The noise could be clearly heard in the area of the first crankshaft main bearing;
• The noise would not be present when the poly-V belt was removed;
• The noise was a pulse-like crackling that occurred at irregular intervals; and,
• 20 pulses (ticking) represented a ‘justifiable complaint’.

These symptoms were attributed to a ‘run-in effect’ or defect of the first crankshaft main bearing shells. To verify the complaint, the poly-V belt was to be removed to see if that eliminated the noise. To fix, the bearing shells of the first crankshaft main bearing were to be replaced.

Oil cooler leaks

Pre-2010 OM642 engines were susceptible to oil cooler leaks due to heat-related seal degradation. In 2010, Mercedes-Benz introduced more durable Viton seals which could be identified by their purple colour (the previously used seals were orange).

TWC temperature sensor

The TWC temperature sensor (part no. A005 153 40 28) was susceptible to failure and was subsequently replaced with part no. A007 153 74 28. When the temperature sensor fails, the check engine light may illuminate and issue the OBD-2 diagnostic code P2031.

Swirl valves, blown fuse and ‘limp home’ mode

The positive crankcase ventilation system vents to the inlet of the turbocharger. However, the vented air may contain too much oil to easily pass through the swirl motor valves which are downstream of the turbocharger. Once this oil and sludge begins to accumulate, the swirl motor valves may become inoperative and blow a fuse that controls other sensors which are required for the engine and emissions systems to operate properly. As a result, the vehicle will enter ‘limp home” mode and limit engine speed to 3000 rpm.