Mercedes-Benz E 450
Return to the inline-six after years of the M276 V6 — and the difference is immediately noticeable. Smoother, more even rev build-up, torque plateau from 1,600–4,000 rpm without any weakness. The 48V mild-hybrid system with integrated starter-generator (ISG) is not a marketing term: 16 kW of boost on pull-away fills turbo lag completely; measurable fuel saving in sail mode. When buying, check the 48V battery — failure costs 2,000–4,000 EUR, primarily affecting build years up to 2022. Electric coolant pumps can fail from 80,000 km. Change oil every 10,000 km, do not rely on Longlife — HPFP and camshaft adjusters are sensitive to old oil. Cold-start wastegate bushing rattle is by design and not a fault. Overall a very accomplished engine that holds 250,000 km without issues when maintained correctly.
E450 T-Model — Inline-Six Estate for High-Mileage Drivers
270 kW in the E-Class estate: the most sensible way to drive the M256. Large boot, all-wheel drive, 48V mild hybrid — under 9 litres on motorways is achievable. The inline-six gives the T-Model a composure four-cylinders cannot match. No adrenalin, but an all-round convincing powertrain for families and high-mileage drivers.
Engine Weaknesses 9
Frequently reported problem: 48V battery of the EQ Boost system fails and costs 2,000–4,000 EUR to replace. Design issue with earth connection in early vehicles.
Symptoms: EQ Boost deactivated, start-stop system failed, hybrid warning light, sporadic starting problems
The known Mercedes problem of leaking camshaft solenoids also affects the M256 (same solenoid technology as M276/M270). Oil migrates by capillary action and destroys lambda sensors and the ECU.
Symptoms: Lambda sensor fault codes, MIL, rough running. Multiple electrical faults simultaneously as it progresses
M256 shows elevated oil consumption from approx. 100,000 km, attributable to the PCV system and cylinder walls. Regular oil level checks necessary.
Symptoms: Dropping oil level, occasional bluish smoke after warm-up phase
The beltless M256 operates exclusively electric coolant pumps. Pump motors fail internally and trigger temperature warnings. Bleeding requires specialist diagnostic equipment.
Symptoms: Coolant temperature warning, irregular operating temperature, occasional overheating warning
The camshaft-driven high-pressure pump on the M256 can wear prematurely with irregular oil changes. Injectors can be damaged by metal debris.
Symptoms: Fuel pressure fault codes, rough idle, starting problems, hesitation under load, elevated fuel consumption
With predominantly short-trip use the OPF cannot fully regenerate. Power drop and elevated consumption result. Virtually no risk for motorway drivers.
Symptoms: Power drop at higher load, elevated fuel consumption, occasional particulate filter warning, engine runs rougher
The M256 uses Camtronic variable valve actuation — same technology as M276/M270 with documented failures. Wear on the adjustment unit or solenoid valve is possible. Oil quality is decisive.
Symptoms: Hesitation at low rpm, camshaft position sensor fault code, rough idle, engine warning with power reduction
Direct injection on the M256 inline-six causes carbon deposits on intake valves. Walnut blasting every 60,000–80,000 km recommended.
Symptoms: Hesitation in the lower rev range, rough idle, sporadic misfires on cold start
Rattling on cold start from the wastegate guide bush with design-inherent play. BorgWarner states this is necessary so the wastegate does not stick at operating temperature. Mercedes classes it as state of the art — not a defect.
Symptoms: Rattling or clattering in the first seconds after cold start, disappears after warm-up
Vehicle Weaknesses 14
An incorrectly routed gearbox wiring harness allows water ingress with an increased fire risk. Mercedes issued a recall.
Following software updates, the ECU in individual C238 units was permanently damaged. One owner reported a seven-month workshop stay.
A serial design defect: the tension cables in the soft-top headliner fray and snap after approximately 200–300 roof cycles. Mercedes revised the design from May 2020.
The electric parking brake generates fault messages and seizes, particularly in cold weather. Grinding noises when applying indicate worn components.
The soft-top tension cords fray after just a few hundred opening cycles. A design fault that led Mercedes to carry out goodwill repairs.
At higher mileages the electric motors in the roof kinematics or the hydraulic unit can fail. The roof can then no longer open or close fully.
Brake discs on the W213 show juddering after just a few thousand kilometres. Individual cases report renewed juddering after warranty replacement.
Elevated MOT failure rates at suspension mounts. The double wishbone front axle shows wear at bearings and joints.
Infotainment and driver assistance systems are prone to faults. Brake assist and cruise control warning messages appear without cause. Often resolved via software update.
The electric parking brake is prone to corrosion and seizing. Multiple recall actions for the brake system have been documented.
The electric parking brake generates fault messages and seizes, especially in cold weather. Grinding and creaking noises when releasing are common.
The optional Airmatic air suspension is prone to compressor and air bag failures. Replacement requires removal of the rear axle and is expensive.
The rotary push controller on the centre console is mechanically fragile and shows signs of failure after heavy use.
MBUX system freezes or reboots. Bluetooth connections drop, voice control unresponsive. Software updates only fix some issues.