Mercedes-Benz S350 W220

The AIRMATIC system is the W220's most notorious weak point. Air struts develop leaks at the rubber bellows as they age, causing the car to sag on one or more corners. The compressor then works overtime to compensate, eventually burning out. The compressor relay (Tyco type) is another common failure point: its contacts can stick closed, causing the pump to run continuously until it self-destructs. Symptoms include an uneven stance after sitting overnight, suspension warning messages, and compressor noise. A single aftermarket air strut costs €400-600 installed at a specialist; OEM struts run €800-1,200 per corner. A new compressor with relay runs €600-900 installed. On a 20-year-old W220, expect at least one or two corners to need attention. Post-2003 facelift cars use slightly improved struts, but age is the primary factor at this point. Some owners convert to conventional coil springs (€800-1,200 for a kit), which eliminates the problem permanently but sacrifices ride quality.

The W220 S-Class (post-facelift models from 2002 onwards) uses Mercedes' Sensotronic Brake Control, an electro-hydraulic braking system. The SBC pump/accumulator can fail, causing a dashboard warning and fallback to conventional hydraulic braking with increased pedal effort. The system has a built-in lifecycle counter that triggers a warning after a set number of brake applications regardless of component condition. Mercedes extended the SBC warranty to 25 years with unlimited mileage in the US, but this extension does not apply universally in Europe. Replacement of the SBC hydraulic unit costs €1,500-2,800 depending on whether new or remanufactured parts are used. Specialist repair outfits can refurbish the unit for less. Always test the brakes thoroughly during a test drive, including emergency stops from moderate speed.

The 722.6 5-speed automatic is fundamentally reliable, but its 13-pin electrical connector is a known weak point. Transmission fluid can wick up through the connector O-rings into the wiring harness, eventually reaching the conductor plate (valve body controller) and causing it to malfunction. Symptoms include delayed gear engagement, harsh shifts, and limp mode (stuck in 2nd gear). The connector and O-ring replacement is a €50-100 repair if caught early. If the conductor plate itself is damaged, replacement costs €400-800 at a specialist (dealer quotes €1,400-1,800). Transmission fluid should be changed every 60,000 km despite Mercedes' claim of a lifetime fill. A transmission service with new fluid, filter, and connector inspection costs €250-400 and is strongly recommended.

The Pneumatic System Equipment (PSE) pump is located in the trunk and provides vacuum pressure for door locks, soft-close doors, trunk operation, and front seat lumbar support. When it fails, multiple convenience features stop working simultaneously. The pump's plastic discharge port can melt from heat when the pump runs excessively (often caused by a vacuum line leak elsewhere). A new PSE pump costs €300-500 for the part, with €100-400 for installation and diagnostics. Before replacing the pump, check vacuum lines and door actuators for leaks, as these can cause the pump to overwork and fail prematurely.

The W220 is notorious for parasitic battery drain. The car's numerous control modules (CAN bus network) may fail to enter sleep mode, drawing well above the acceptable 50 mA standby current. Common culprits include the COMAND head unit, door control modules, trunk soft-close mechanism, and aftermarket accessories. Diagnosis requires systematic fuse-pulling with an ammeter to isolate the offending circuit. A healthy W220 should draw under 50 mA when fully asleep (which can take up to 45 minutes after locking). Solutions range from simple (replacing a faulty relay, €50-100) to complex (replacing a control module, €400-800). Many owners install a battery disconnect switch or trickle charger as a workaround.

The M112 engine's crankshaft position sensor is a well-known failure item. When it starts to degrade, the engine will intermittently fail to start when hot (after a short stop at a petrol station, for example), but starts fine once it cools down. Failures become more frequent as the sensor deteriorates further. The sensor is located at the rear of the engine near the firewall, making access difficult and increasing labor time to 1.5-2 hours. The part costs €50-80; total repair at a specialist is €200-400. This is one of the most common M112 issues but is inexpensive and straightforward once diagnosed.

The M112's valve cover gaskets and rear camshaft plugs are common oil leak sources on high-mileage engines. The gaskets harden over 15-20 years and begin seeping oil down the sides of the engine. The rear camshaft plugs (3 plastic pieces costing about €20 for the set) are another frequent leak point. A complete valve cover gasket replacement on both banks costs €300-600 at an independent specialist, with OEM gaskets recommended over aftermarket for longevity. Left untreated, oil can drip onto exhaust components, creating a burning smell and potential fire hazard.

Mercedes did not fully galvanize body panels on the W220 until approximately 2004 production. Earlier cars used wax-based protection that deteriorates over time, leading to rust on door bottoms, wheel arches, front fenders where they meet the bumper, and the trunk lid. Some owners report corrosion on the sunroof frame and A-pillars as well. Repair costs depend heavily on severity: catching and treating surface bubbles early costs €200-500, while extensive panel replacement and repainting can reach €2,000-3,000. Cars from salt-heavy regions are significantly more affected. The European rust perforation warranty covered 30 years from new, but any cosmetic/structural rust discovered at this age is the owner's responsibility.