Mercedes-Benz C 300 de
Completely new aluminium diesel with NANOSLIDE coating and integrated particulate filter. Noticeably quieter and cleaner than the OM651. Few typical faults known to date.
306 hp Diesel Hybrid
225 kW system output with 700 Nm torque — powerful thrust and electric gliding alternating.
Engine Weaknesses 11
Known weak point: the narrow camshaft lobes and rocker arms in the OM654 wear prematurely due to inadequate lubrication. Mercedes issued TSBs.
Symptoms: Ticking or knocking from engine bay, misfires, rough running, engine warning light
Over 800,000 Mercedes diesel vehicles with OM654/OM656 were recalled due to a leaking electric coolant pump. Coolant loss can lead to overheating.
Symptoms: Coolant loss, overheating warning, coolant warning light, engine temperature rises
NOx sensors wear out from soot particles and deliver erroneous readings. Consequence: incorrect AdBlue injection, CEL illumination; if unaddressed, an engine start inhibit may follow. Both sensors can be affected.
Symptoms: CEL, AdBlue warning, fault code P20EE or P204F, message 'No start after X km', rough idle
Early OM654 units had overly soft rocker arms. From engine number 80278367 (10/07/2018) a reinforced version A6540505701 was fitted. Older examples may develop camshaft damage.
Symptoms: Clattering or ticking noise in the valvetrain, poor cold start, increased oil consumption, rough idle
Recall (action code 0591016) affects approximately 10,700 vehicles (built 01/2016–02/2021): individual bolts or chain links wear and can cause chain snap with engine damage.
Symptoms: Rattling on cold start, sudden power loss and engine damage in the event of chain snap, engine warning light
A blocked DPF or coked EGR increases exhaust back pressure. The pressure pushes the turbo shaft axially into the compressor housing, the thrust bearing wears and the turbocharger fails.
Symptoms: Power loss and boost pressure fault, blue smoke from exhaust, whistling from turbocharger, oil leaking from turbo
With predominantly short-trip use the OM654 DPF does not regenerate fully. Leads to oil dilution from stored diesel fuel and premature DPF blockage.
Symptoms: DPF warning light, rising oil level from fuel dilution, power reduction
EGR valve coking up with frequent short-distance use. Clogged passages cause juddering, fault codes and limp mode. Euro 6d exhaust gas recirculation is heavily loaded by design.
Symptoms: Juddering and power loss at part throttle, CEL, increased fuel consumption, rough idle
DPF does not regenerate fully during short-distance driving. Accumulating soot particles lead to warnings, limp mode and, if neglected, filter replacement or engine damage through oil dilution.
Symptoms: DPF warning light, increased fuel consumption, power reduction, engine oil smells of diesel from post-injection
With frequent short-trip driving unburnt fuel enters the engine oil through DPF post-injection. This dilutes the oil, reduces lubrication, and promotes wear in the valve train.
Symptoms: Oil level rising above maximum (oil increase), frequent DPF regeneration cycles, engine warning light, limp mode after aborted regenerations
The OM654 high-pressure injection system operates at up to 2,050 bar. At high mileage or with poor fuel quality, injectors wear and develop quantity errors.
Symptoms: Juddering and knocking, rough idle, starting problems, elevated fuel consumption, in extreme cases cylinder misfires
Vehicle Weaknesses 7
Longitudinal members, jack-point attachment holes and rear axle subframe rust through. MB offers goodwill replacement.
Polycarbonate blind cover of the panoramic roof incorrectly bonded. When opening, the blind can come loose. Recalled by MB.
Ball joints on the wheel-side wishbone and rubber-metal bushes wear. New suspension geometry makes repairs more involved.
Some W205 models discharge the battery unusually quickly during extended parking. Cause: elevated quiescent current draw from control units.
The W205 shows above-average front axle issues from the second MOT onwards according to TÜV statistics. Worn control arms and drop links are the main causes.
W205 A/C fails with 'Air conditioning off' without a fault code in the onboard computer. Often the compressor or A/C control unit is defective.
Panoramic roof on the W205 creaks when opening and closing. Guide linkage can bend and jam the roof. Repair often requires complete removal.