Mercedes-Benz S 320 CDI

The Bosch high-pressure pump can cause rail pressure drop at high mileage. Difficult starting and erratic injection behaviour follow.

Symptoms: Hard starting (especially cold), engine only starts after several attempts, hesitation under load

The OM648 uses Bosch high-pressure injectors that tend to leak at high mileages. A faulty injector leads to poor combustion and increased soot production.

Symptoms: Rough idle, black smoke, power loss, frequent DPF regeneration, rising oil level

The OM648 turbocharger suffers bearing damage from insufficient oil supply or contaminated oil. Faulty oil return lines and blocked oil drillings contribute to the damage.

Symptoms: Whistling or rattling from the turbo area, blue smoke under acceleration, oil loss at the turbo

The crankshaft torsional vibration damper (harmonic balancer) disintegrates. Can cause severe engine damage if not replaced in time.

Symptoms: Vibrations at certain rpm ranges, knocking noise from the front, belt thrown off

Injectors develop leaks at the sealing seat. Two injector generations (with/without IMA coding) create confusion. Wrong types cause injection quantity problems.

Symptoms: Hissing at the injector head, oil film on injector bolts, rough running, elevated quantity correction values

The OM648 tends to timing chain rattle after cold start at higher mileages. Initially audible for only a few seconds, later persistent.

Symptoms: Metallic rattle after cold start (30–60 seconds), rpm-dependent rattling at 1,500–2,500 rpm

The OM648 oil cooler gaskets harden with age and develop leaks. The gasket itself is inexpensive, but replacement requires removal of the intercooler and coolant lines.

Symptoms: Oil drops bottom-right of the engine, oil smell after driving, dropping oil level with no other leaks visible

The OM648 dual-mass flywheel wears at high mileages. Repair usually includes the clutch as well and is carried out as a complete package.

Symptoms: Rattling and knocking when changing gear, vibrations at idle especially on shut-down, metallic noises

The Airmatic compressor runs continuously when there are leaks in the system and burns out. Without swift intervention, total suspension failure and blocked ride-height control follow.

Air spring bag seals age and become leaky. The vehicle drops on one side or completely. All four struts typically need replacement by around 250,000 km.

Three SAM modules in the engine bay and interior are vulnerable to water ingress through blocked drain channels. Secondary damage can exceed the vehicle's residual value.

The hollow-section sills of the W220 rust from the inside out. Nothing is visible externally for a long time until the rust is already well advanced. Pre-facelift models (1998–2002) are particularly affected.

The W220 rusts at the underbody, wheel arches and weld seams, particularly where underbody protection has not been renewed regularly.