Mercedes-Benz S 350d
Modern inline-six diesel with aluminium block and steel pistons. Efficient and powerful, few known weaknesses to date. Timing chain long-lived.
Diesel Cruiser
210 kW Diesel — sovereign and economical on long motorway runs.
Engine Weaknesses 6
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
Vehicle Weaknesses 14
The active electro-hydraulic ABC suspension requires intensive maintenance. Hydraulic lines, valve blocks and pumps can develop leaks. Hydraulic oil change required every 50,000 km.
Air bags and pressure hoses develop leaks. The compressor runs continuously and overheats. Repair: air bag pair 2,500–3,500 €, compressor 1,000–1,300 €.
Air struts on Airmatic and Magic Body Control suspensions develop leaks. Vehicle drops, suspension warning light appears. Repair per corner is very costly.
The hydraulic Magic Body Control suspension is prone to valve block and hydraulic pump failures. Contamination in the oil causes system failures.
The COMAND infotainment system freezes sporadically or fails completely. System faults increase from around 100,000 km.
Radar and camera sensors for adaptive cruise control and emergency braking can cause malfunctions due to dirt or defects. Calibration after repair is expensive.
The COMAND navigation system shows read errors, freezes or fails to boot. A defective drive unit is the most common cause.
Matrix LED headlights are not repairable -- individual modules cannot be replaced. Moisture and electronic failures require complete headlight replacement.
Window regulators fail or become unresponsive. Cause is often a software fault in the door control unit, fixable by update.
Brake discs and pads wear quickly due to the high vehicle weight. Particularly during spirited driving.
The pneumatic control unit operates soft-close, central locking and rear headrests via a shared pump. Leaks cause all functions to fail simultaneously.
The Comand NTG5 infotainment system shows display failures, freezing and navigation start errors. Temperature-dependent malfunctions occur frequently.
Seat heating mats and massage pneumatics in the multicontour seats are wear items. Heating mats fail internally, the PSE pump loses pressure for the massage function.
The rubber seal of the Keyless Go microswitch in door handles becomes brittle through UV and temperature cycling. Moisture enters, the switch corrodes.
Reports & Tests
187 owner complaints filed with NHTSA (2013–2020). Most reported: Other (43), Steering (22), Engine (20).