Car Model Guide/ Mercedes-Benz/ C-Class/ W204/ C 320 CDI OM642/ Issues

C 320 CDI OM642, known issues

W204 · 2007–2011 · R3 Demands diligence

Recorded issues6
Walk-away0
Over €1,0004
Checkable at viewing2/6
Likely spend€2,950

Likely spend is the mid cost of every issue rated common or universal, added together, what an unmaintained example owes over the next few years, not a prediction for any one car. Worst case if everything here failed at once is €7,600, which isn't a realistic scenario but is a useful ceiling.

All issues, by system

Engine

Oil cooler seal leakOM642 3.0 V6 CDI€900–€1,600
Oil weeping down the back of the block, burning smell, oil in the valley beneath the intake. The oil cooler sits in the vee under the intake manifold and its seals harden with age. Access requires the intake off, so labour dominates the bill.
Check: Look down the back of the engine with a torch for wet oil and fresh cleaning. A suspiciously spotless engine bay on a 200,000 km V6 deserves a question.
EnginecommonDetectable at viewingevidence: documented150–280k km

Emissions

DPF clogging and forced regenerationDPF€250–€1,800
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.
EmissionscommonPartly detectableevidence: documented120–250k km
EGR cooler leakEGR cooler€400–€1,000
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.
EmissionsoccasionalPartly detectableevidence: manufacturer120–250k km

Transmission

7G-Tronic conductor plate and 13-pin connector leak (722.9)Mercedes 7G-Tronic seven-speed automatic (722.9)€400–€900
Harsh, delayed or jerky shifts, holding a gear then banging the next in, and limp mode, often with speed-sensor or gear-ratio fault codes. The speed sensors in the conductor plate (mechatronic) fail, and/or the external 13-pin connector leaks fluid that wicks up the wiring into the control unit. Early units are the most affected.
Check: Test-drive through every gear cold and warm. Scan the transmission, and pull the external 13-pin plug to check for fluid on the pins.
TransmissioncommonPartly detectableevidence: documented120–220k km

Electrical

Electronic steering lock failureW204 body€600–€1,400
Key won't turn, no crank, or a car that starts intermittently and then refuses. The electronic steering lock module fails, immobilising the car. It strands rather than degrades.
Check: Can't be checked reliably on a viewing, it fails without warning. Ask whether it has been replaced; a receipt is worth having, and a car that has already had one is lower risk than one that has not.
ElectricaloccasionalNot detectable at viewingevidence: documented80–200k km

Turbo & intake

Intake-port shut-off (swirl) actuator failureOM642 3.0 V6 CDI€400–€900
Limp mode and power loss, usually with fault code P2015 stored. The actuator motor that drives the intake-port shut-off flaps in the manifold fails, frequently after being shorted by oil dripping from the turbo-inlet seal above it; the flaps or linkage can also seize.
Check: Scan for P2015 and related intake codes; a car that has thrown it before is likely to again unless the oil-leak cause was addressed.
Turbo & intakeoccasionalDetectable at viewingevidence: documented120–220k km

How to read this

Every issue is authored once against the part that actually carries it: the engine, the gearbox, the chassis or a shared component, and inherited by every variant that has that part. The badge next to each issue says where it comes from, so you can tell an OM642 problem from an E9x problem.

Evidence tiers. Manufacturer means a recall, technical bulletin or revised part number. Documented means workshop data or multiple independent sources. Reported means owner consensus with no hard confirmation, and never sets a risk level on its own.

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