Mercedes-Benz C 320
Three-valve V6 with individual ignition coils. Smooth and strong. Typical weak points: crankcase breather and intake manifold flaps. High mileages achievable.
V6 Power Without Compromise
160 kW V6 M112 — powerful, refined, without the nervy edge of a supercharger. The W203 with this engine feels like a genuine business sports car.
Engine Weaknesses 7
The camshaft adjuster solenoid on the M112 develops a leak and draws oil by capillary action into the wiring harness. Oil can migrate as far as the engine ECU and destroy it.
Symptoms: Cold-start rattling that disappears after 1–2 seconds, camshaft adjuster fault code, oil traces at wiring connector, later ECU faults
The vacuum hose for the variable intake manifold on the M112 becomes brittle and breaks. The swirl flaps stick. The hose is not available individually — the entire intake manifold is needed.
Symptoms: Power drop, slight hesitation at part throttle, engine runs but without full power
On the M112 V6 the valve cover gaskets become porous over time. Especially the rubber seals on the front cover between the timing cover and engine block fail on virtually all high-mileage M112 engines.
Symptoms: Oil spots on the floor, oil smell after driving, oily engine bay, dropping oil level
The plastic linkage of the variable intake manifold in the M112 typically breaks around 150,000 km. The actuator and tumble flaps freeze in one position — according to forum reports, all M112 engines are eventually affected.
Symptoms: Engine enters limp mode, power drop at higher revs, intake flap fault code, stumbling on acceleration
The M112 V6 has two spark plugs per cylinder sharing a dual-output ignition coil. Neglected plugs prematurely destroy the coils.
Symptoms: Rough idle, individual cylinder misfires, CEL, power loss at cold start
The crankcase ventilation membrane in the M112 wears and causes elevated oil consumption and engine sweating. Engine power can also drop due to false air ingestion.
Symptoms: Oil consumption above 1 L/5,000 km, light oil mist in engine bay, smoke from exhaust
The thermostat on the M112 V6 can stick in the open position. Engine only reaches 70–80°C instead of the target 87°C. Result: increased fuel consumption, poor heater output.
Symptoms: Engine doesn't warm up properly, heater stays cold, increased fuel consumption, temperature gauge permanently low
Vehicle Weaknesses 7
Rear subframe rusts from the inside out. Critical weak point as spring mounts can break away. Pre-facelift models up to 2004 particularly affected.
W203 up to the facelift of March 2004 particularly rust-prone: wheel arches, sills, door lower edges and tailgate. Rear subframe can rust through on older examples.
Rust starts on the rear wheel arches, followed by sills, door lower edges and tailgate. Unsealed flanges encourage corrosion.
MOT regularly cites anti-roll bar mountings, suspension springs and tie rod ends. Common cause of inspection failure on older examples.
Early W203 models (before March 2004) suffer from wiring breaks in electric seats and steering column stalks. SAM module failures documented.
W203 steering jolts during steering movements or is heavy. Causes: worn control arms, track rod ends or defective power steering pump.
SAM modules on the W203 control lighting, wipers and vehicle electrics. Moisture and ageing lead to sporadic complete failure of multiple systems simultaneously.