Mercedes-Benz S320 CDI W220

The AIRMATIC suspension is standard on the W220 S-Class and the rubber bladders degrade with age. Rear springs typically fail first. Symptoms include one corner sitting lower after overnight parking, the car listing to one side, or the compressor running constantly. Early pre-facelift cars (1999-2002) have worse reliability than the running change from late 2003 onwards. OEM strut replacement at a Mercedes dealer costs €600-800 per corner, while aftermarket alternatives from Arnott or Bilstein run €250-400 per strut. If the compressor pump fails from overwork due to leaking springs, add €400-700 for the pump. A full suspension refresh covering all four struts plus compressor reaches €2,500-3,500 at a dealer. Coil spring conversion kits are available for €800-1,200 as a permanent fix, but they eliminate the ride comfort that defines the S-Class. Most W220s with over 100,000 km will need at least one strut replaced.

The OM613/OM648 common rail system relies on a fuel rail pressure sensor and a fuel cut-off valve (pressure regulator) that deteriorate over time. The pressure sensor can fail or produce erratic readings, leading to uncertain starting, unstable idle, fluctuating revs, and diagnostic error codes. The fuel cut-off valve can also fail entirely, starving the engine of fuel. The pressure sensor itself costs €80-150 and is straightforward to replace. However, if the regulator or high-pressure fuel pump has also degraded, combined repair costs reach €800-1,200. This is one of the most commonly reported drivability issues on the OM613 and OM648 engines. Using clean, high-quality diesel and replacing the fuel filter at every service interval helps extend the system's life.

The copper sealing washers under the injectors degrade over time, allowing exhaust gases and soot to leak around the injector seats. This creates a buildup of hard carbon deposits around the injectors. If caught early, replacing the washers and cleaning the seats costs €200-400. However, if left too long, the carbon deposit welds the injectors into the cylinder head, making removal extremely difficult. Seized injectors often require specialist extraction tools or even cylinder head removal, pushing costs to €1,500-2,500. The OM648 engine is particularly susceptible because its aluminium cylinder head allows more thermal expansion than the OM613's iron block. A preventive reseal every 80,000-100,000 km is strongly recommended.

Mercedes did not fully galvanise W220 body panels until late 2004. Earlier cars used a wax-based protection that fails over time, particularly in salt-belt regions. Rust commonly appears on the wheel arches (front and rear), the boot lid (especially around the licence plate recess), the sills, and less visibly on the subframe mounting points and suspension turrets. Boot lid springs also corrode and break, which is nearly universal on W220s. Surface rust repair per panel costs €300-600 for a body shop respray, but structural rust in the sills or subframe mounts is far more serious and can render the car uneconomical to repair. Facelift cars (2003-2005) are less affected but not immune. Always inspect the underside on a lift.

The crankshaft position sensor on the OM613/OM648 is prone to heat-related failure. The sensor's internal resistance changes when hot, causing the signal to drop out. Typical symptoms include the engine stalling after a long drive and refusing to restart until it has cooled down for 30-60 minutes. The part is inexpensive (€30-60) and replacement is straightforward, taking about an hour. However, diagnosis can be time-consuming if the mechanic is unfamiliar with this well-known issue. The camshaft position sensor can also fail with similar symptoms. Replacing both sensors preventively costs €100-200 in parts plus labour and is recommended at the first sign of intermittent hot-start problems.

The 722.6 five-speed automatic is generally robust, but Mercedes marketed its transmission fluid as a lifetime fill, which it is not. Degraded fluid causes rough shifting, delayed gear engagement, and occasional limp mode. A fluid and filter change costs €200-350 and often resolves symptoms. If the conductor plate (the electronic control unit inside the transmission) has degraded, replacement costs €600-1,200. In some W220s, a faulty Valeo radiator can allow coolant to mix with the transmission fluid through the internal oil cooler, which causes catastrophic transmission damage. If the fluid appears pink or milky, walk away. Regular fluid changes every 60,000 km are strongly recommended despite the factory claim.

The W220 has extensive electronic systems that draw power even when the car is off. When any control module fails to enter sleep mode, parasitic draw exceeds the normal 40-60 mA range and flattens the battery. Common culprits include the COMAND infotainment system, the trunk soft-close mechanism (a stuck trunk release button can draw 5 amps continuously), and door control modules. A new battery costs €150-250, and diagnosing the draw by systematically pulling fuses can take several hours at a specialist (€150-300 in diagnostic time). A quality trickle charger is essential if the car is not driven daily.

The OM613 and OM648 use vacuum-controlled turbocharger wastegate actuators. Over 20+ years, the rubber vacuum hoses become brittle and crack, causing boost leaks that result in limp mode and reduced power. Replacing the vacuum lines is a straightforward and inexpensive fix (€50-100 in parts). However, if the wastegate actuator itself has seized or the turbo has developed internal wear from oil supply problems, a reconditioned turbo costs €800-1,200 and a new unit €1,500-2,500. The OM648 is slightly more prone to turbo issues than the OM613 due to its higher output. Symptoms include black smoke under load, whistling sounds, and the EPC warning light combined with reduced power.

The OM648 engine (2003-2005 facelift models) has variable geometry swirl flaps in the intake manifold that progressively clog with carbon deposits from EGR gases. Symptoms include rough idle, reduced power, and intake system error codes. Cleaning the manifold and flaps costs €300-500 at a specialist. Some owners choose to remove or blank the flaps entirely, which eliminates the problem but may affect low-speed torque characteristics and emissions compliance. This issue does not affect the earlier OM613 engine which does not have variable geometry intake flaps. Regular motorway driving at higher loads helps keep the flaps cleaner.