Mercedes-Benz CLS 400 d

The vacuum-controlled coolant pump can develop leaks between the coolant and vacuum circuits. Coolant enters the EGR solenoid valves; an electrochemical reaction creates a fire hazard.

The Bosch CP4 high-pressure pump is more sensitive to fuel contamination than its predecessors. Poor diesel quality can damage the pump and injectors.

Symptoms: Power loss, hesitation, injection system fault codes, in severe cases engine damage from metal swarf

The switchable coolant pump does not reliably seal between the coolant and vacuum circuits. Coolant can overheat electrical solenoid valves — fire risk. Campaign code 2090008.

Symptoms: No direct driver symptoms — preventive recall. Possible coolant loss, electrical faults, unusual odour

Early OM656 units had overly soft roller rocker arms. From engine number 80278367 (10/07/2018) a reinforced version was fitted. Older engines develop camshaft wear and timing chain problems.

Symptoms: Clattering tick in the valvetrain, especially on cold start, increased oil consumption, CEL, rough running

The variable valve lift system Camtronic shows failures at solenoid valves and actuators, especially up to 2022. Camshaft wear generates metal particles in the oil.

Symptoms: Rough idle, knocking noises while driving, elevated oil consumption, variable valve train fault code

DPF, EGR and SCR/AdBlue system are sensitive to frequent short-trip driving. Premature blockages with warning lights are common.

Symptoms: Engine warning light, DPF warning lamp, power reduction in regeneration mode, elevated AdBlue consumption

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.