Mercedes-Benz CLS 350
Four-cylinder turbo with 48V belt starter-generator. Modern, efficient engine with EQ Boost mild hybrid. Timing chain long-lived.
Solid Foundation
220 kW — practically motored for everyday use, nothing exciting.
Engine Weaknesses 12
Defective exhaust valves and soft valve guides lead to severe cylinder head damage. Often just after the warranty expires. Mercedes USA extended the warranty to 15 years/150,000 miles.
Symptoms: Sudden severe misfires, CEL flashing, power drop, dangerous stalling at motorway speed
The electric motor is integrated into the 9G-Tronic. With faults in the high-voltage cables the gearbox must be removed — extremely costly repair.
Symptoms: Fault message 'Hybrid drivetrain disturbed', no electric drive possible, vehicle runs as pure combustion engine only, sometimes emergency shutdown
The hydraulic chain tensioner on the M264 can lose oil pressure after extended standstill. On cold start the timing chain rattles briefly until oil pressure builds.
Symptoms: Brief rattling on cold start (2–5 seconds), disappears after warm-up
The integrated starter-generator (ISG) of the M264 EQ Boost system can fail. Start-stop function and boost support are lost. Expensive replacement.
Symptoms: Start-stop function deactivated, no EQ Boost on pull-away, 48V system fault message, rougher engine start
The M264 uses multiple electric coolant pumps. Internal motor defects trigger fault codes. Bleeding requires the Mercedes diagnostic tool.
Symptoms: Coolant temperature warning, fault codes P0A0500/P00B700/P0C7300, irregular engine temperature
The PHEV lithium-ion battery measurably loses capacity at high mileage. Faulty temperature sensors can trigger emergency shutdown of the hybrid drivetrain.
Symptoms: Electric range drops significantly, warning 'Stop immediately', unexpected shutdown of hybrid drivetrain
The 48V lithium-ion battery of the EQ Boost system loses capacity over time. With severe degradation the boost function is curtailed.
Symptoms: Reduced EQ Boost output, more frequent start-stop deactivation, 48V warning on display
The camshaft adjuster solenoid valves on the M264 can leak internally. Variable timing no longer functions correctly, engine runs rough.
Symptoms: Rough idle, camshaft position fault codes, slight power loss in the lower rev range
Direct injection without port injection leads to carbon deposits on intake valves, especially with short-trip use. Impairs intake flow and combustion.
Symptoms: Hesitation and rough idle from approx. 80,000 km, slight power drop, elevated fuel consumption, knock tendency under load
The OPF requires temperatures above 600°C for active regeneration. With frequent short trips under 10 km the filter cannot regenerate and becomes progressively blocked.
Symptoms: Check engine light, elevated fuel consumption, forced long-distance drive needed for regeneration, engine power reduced
Turbocharging and direct injection thermally stress spark plugs more heavily. Ignition coils can electrically fatigue at high mileage and cause misfires.
Symptoms: Misfires, rough engine running, hesitation on acceleration, check engine light, poor throttle response
Valve cover gasket and rear crankshaft seal tend to leak at higher mileage. Oil loss on the hot engine can cause smoke.
Symptoms: Oil smell when parked, visible oil puddles under the vehicle, dropping oil level, bluish smoke from engine bay
Vehicle Weaknesses 7
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.
Reports & Tests
32 owner complaints filed with NHTSA (2018–2024). Most reported: Wheels (15), Electrical (9), Engine (4).