Mercedes-Benz CLS 300d

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

Retaining screws for the turbocharger oil return line may be mixed up. Incorrect screws reduce clamping force, oil can escape and ignite.

C257 AIRMATIC air springs lose pressure over time. Compressor runs frequently and wears additionally. Individual air spring 800–1,500 EUR, compressor 500–1,000 EUR.

MOT weak point: hydraulic bushing on the front axle tie rod. Upper wishbone also frequently cited.

MBUX infotainment and driver assistance systems tend to crash and malfunction. Software updates do not fix all cases.

After map or OTA software updates, the COMAND system can get stuck in a boot loop. Navigation, radio and all MBUX functions fail. Workshop stays of up to 14 days documented.

The optional Air Body Control suspension is prone to leaks at the valve block and air lines. The valve block is a frequent cause — dirt prevents it from sealing properly.

9G-Tronic shows temperature-dependent shift shudder and pull-away problems. Typical after 50,000–70,000 km. Software updates can help but don't always resolve it completely.