Mercedes-Benz C 200 CDI
Mercedes' first common rail diesel. Economical and torquey, but prone to injector problems and torque limiter failures.
Uninspiring Entry Diesel
90 kW CDI is enough for everyday driving and nothing more. The W203 is capable of better — this engine does not show it.
Engine Weaknesses 6
The dual-mass flywheel on the OM611 wears particularly quickly with a manual gearbox due to the high torque at low revs. LUK recommends preventive replacement from 150,000 km during clutch work.
Symptoms: Rattling and chattering at warm idle, vibrations when pulling away and changing gear, judder at low revs, noise disappears when pressing the clutch
Injector sealing rings wear and allow combustion gases to escape into the injector bore. Deposits on the seating face make disassembly considerably harder.
Symptoms: Poor cold starting, rough idle, faint hissing with engine running, increased fuel consumption
Plastic inlet channel shut-off flaps become brittle through EGR soot deposits and break. Fragments can enter the engine.
Symptoms: Hissing on acceleration, reduced engine braking, engine warning light, power drop
The vacuum actuator for boost pressure control fails; the turbocharger has no more boost pressure regulation. Often only the actuator is defective, but the turbo unit must be replaced.
Symptoms: Severely reduced acceleration, black smoke under load, limp mode, boost pressure fault message
The EGR valve on the OM611 becomes contaminated with soot and carbonised oil and can no longer close fully. Typical problem with short-trip and taxi use.
Symptoms: Power loss, limp mode, engine won't rev past 3,000 rpm, smoke on acceleration, rpm fluctuations at idle
On the OM611, the O-rings on the fuel filter housing harden and allow air into the fuel system. Engine stumbles or barely starts after extended standing.
Symptoms: Starting difficulties after standing, engine stumbles and cuts out, air bubbles visible in transparent fuel lines
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.