Mercedes-Benz S430 W220

The W220 was the first S-Class with AIRMATIC and the system ages poorly. Rubber air bladders deteriorate and develop leaks, typically starting at the rear between 80,000-150,000 km. A leaking strut causes one corner to drop overnight or after extended parking. The compressor then runs constantly to compensate, which eventually burns it out as well. The OEM relay (Tyco brand) is known to stick, keeping the compressor running even after pressure is restored, accelerating failure. An OEM front strut costs €600-800, a rear strut €400-600. Aftermarket alternatives from Arnott are available for €250-400 per strut. Compressor replacement runs €400-700 including a new relay. A full AIRMATIC refresh (four struts plus compressor) costs €2,500-4,000 at an independent specialist. Coil spring conversion kits are available for €800-1,200, eliminating the system entirely. Pre-2003 valve blocks use integrated solenoids that are more failure-prone than the updated design used from 2003 onwards.

The 722.6 five-speed automatic uses a conductor plate mounted on the valve body that contains speed sensors and solenoid contacts. Over time, these contacts corrode and fail, particularly on cars with infrequent fluid changes. Symptoms include sudden locking into second gear (limp mode), harsh or delayed shifts, and transmission fault codes. The conductor plate itself costs €60-100 as a part. Labor involves dropping the valve body, which runs 3-5 hours at a specialist. Total repair at an independent shop is €500-800. If the problem was ignored and the valve body or internal clutch packs were damaged, a full rebuild can reach €1,500-1,800. Mercedes originally marketed the transmission fluid as a lifetime fill, but specialists strongly recommend changes every 60,000-80,000 km. The 13-pin connector at the transmission can also leak fluid into the TCM, causing similar symptoms. This is a widespread issue affecting all Mercedes models with the 722.6, reported extensively on forums.

The W220 uses an Electronic Ignition Switch (EIS/EZS) that communicates with the key's infrared transponder. Over time, the EIS module degrades, leading to intermittent starting failures that worsen over time. Early symptoms include delayed key recognition or needing multiple attempts to start. Eventually, the car may not start at all. Mercedes dealers quote €1,500-2,500 for a new EIS module with programming. Third-party specialists can repair the existing module for €500-700, which involves resoldering or replacing worn components on the circuit board. The key and steering lock must be matched to the new or repaired EIS. If the ESL (Electronic Steering Lock) also fails simultaneously, costs increase by €300-500. This issue typically surfaces on cars over 15 years old or those with high key-cycle counts.

The W220 is notorious for parasitic battery drain. The car has multiple modules that should enter sleep mode after parking but frequently fail to do so. Common culprits include the COMAND system, the TeleAid module, the PSE pump (soft-close system), door control modules, and the alarm siren. The SAM (Signal Acquisition Module) units can also draw excessive current, especially if water has entered through blocked drainage channels under the rear seat. Normal quiescent draw should be under 80 mA after a 20-minute sleep cycle, but faulty modules can draw 300-500 mA. Diagnosis requires systematic fuse-pulling with an ammeter, which takes 2-4 hours at a specialist. A new battery costs €150-250. Identifying and replacing a faulty module adds €200-600. Owners who park the car for extended periods should use a trickle charger. Three SAM modules are located in the car (two in the engine bay, one under the rear seat), and water ingress into the rear SAM is a particularly common cause.

Bosch supplied wiring harnesses with a biodegradable rubber insulation material designed for easier recycling. Unfortunately, this material degrades over time from engine heat, becoming brittle and crumbling away. The headlight wiring is most commonly affected because daytime running lights generate sustained heat in a confined space. Exposed conductors can short-circuit, causing headlight flickering, failure, or blown fuses. The engine bay harness is also susceptible but degrades more slowly. Aftermarket replacement headlight harnesses are available for €50-100 per side. A DIY repair using liquid electrical tape or heat-shrink tubing is possible for €20-50. If the engine wiring harness needs full replacement, costs reach €800-1,500 including labor. This is an age-related issue that affects nearly all W220s over 15 years old to some degree.

The M113 engine develops oil leaks as the valve cover gaskets and crankcase breather hoses harden with age. The three breather hoses that connect the valve covers to the intake manifold become brittle and crack, often breaking during removal. Oil leaking onto hot exhaust components produces a burning smell. Using only genuine Mercedes gaskets is recommended, as aftermarket gaskets are reported to leak again prematurely. A complete valve cover reseal including gaskets, breather hoses, and new bolts costs €300-500 at an independent specialist and €500-800 at a Mercedes dealer. This typically becomes necessary between 100,000-150,000 km. The rear main seal can also develop leaks at higher mileages, but this is a less urgent concern as it is a slow seep rather than a drip.

The crankshaft position sensor on the M113 is a known weak point, though inexpensive to replace. Typical symptoms start as random stalling that initially resolves on its own, then progresses to more frequent no-start conditions, particularly when the engine is hot. The sensor is located at the rear of the engine near the firewall, making access somewhat awkward. A new OEM sensor costs €30-60, and the repair takes about an hour. Total cost at an independent shop is €100-200. At a dealer, expect €200-300. This is often one of the first engine-related items to fail on the M113, typically between 80,000-150,000 km. Specialists recommend replacing it preventively during other engine work.

The W220 has four catalytic converters (two per bank). The rear catalytic converters are most commonly affected, with their internal ceramic substrate fracturing and rattling inside the housing. This typically produces a distinctive metallic rattling at around 2,500 RPM, particularly when the exhaust system is at operating temperature. Mercedes originally provided an extended warranty of 8 years / 125,000 km for this issue, which has now expired on all W220s. Aftermarket rear catalytic converters are available for €100-200 each, with welding and installation running €100-200 per unit. Full OEM replacement costs €400-600 per converter. Broken substrate fragments can migrate into the muffler but rarely cause drivability issues beyond the rattling noise and potentially failing emissions testing.

The M113 uses hydraulic engine mounts that provide exceptional vibration isolation when new but degrade faster than conventional rubber mounts. Failed mounts produce a noticeable vibration at idle and during low-speed manoeuvres, which is particularly evident in the cabin of an S-Class where refinement expectations are high. The front mounts are more expensive (€120-180 each) than the rear mount (€20-40). Replacement of both front mounts is recommended simultaneously. The top bolt on each front mount is difficult to access, adding labor time. Total replacement cost for both front mounts is €400-600 at an independent specialist and €600-900 at a Mercedes dealer. Mount failure typically occurs between 100,000-150,000 km.