Mercedes-Benz S350d W222

The W222 uses AIRMATIC air suspension at all four corners as standard. While the W222 generation improved significantly over earlier designs, the rubber air spring bladders still deteriorate over time, particularly in climates with temperature extremes. Typical failure appears between 100,000 and 160,000 km. Symptoms include the car sagging at one corner overnight, the compressor running excessively, or suspension warning messages. An OEM strut costs €700-900 per corner, with aftermarket alternatives from Arnott or Bilstein available for €450-650. It is recommended to replace struts in pairs. The compressor itself can also fail from overwork if a leak goes unaddressed, adding approximately €800-1,200 to the repair. W222 owners report fewer failures than W220 or W221, but the issue remains the most common expensive repair on this generation.

The OM642 V6 has its oil cooler mounted deep in the engine valley between the cylinder banks. The original gaskets harden over time and begin to seep oil, typically between 100,000 and 150,000 km. The seal kit itself costs approximately €30-50, but the repair requires removing the turbocharger, intake manifolds, and EGR cooler to access the oil cooler, resulting in 8-10 hours of labor. Total cost at an independent specialist runs €1,200-1,500, while Mercedes dealer quotes can exceed €2,000. Later production OM642 engines received improved sealing material, but the issue is not fully eliminated. Catching the leak early prevents oil contamination of other components.

The copper seals at the base of each diesel injector can degrade over time, allowing combustion gases to escape. This creates a hard, tar-like carbon buildup around the affected injector known as Black Death. Symptoms include a chuffing or ticking noise from the engine bay and black carbon deposits visible on top of the engine. If caught early, replacing the copper washers costs just €5-15 per injector with €150-300 in labor. However, if the carbon buildup is severe, extraction becomes extremely difficult and time-consuming, and a full injector replacement may be needed at €400-600 per injector. This issue is well-documented across all OM642 applications and typically appears after 80,000-120,000 km. Regular inspection of the injector area is the best prevention.

The OM642 uses variable intake swirl flaps controlled by plastic connecting rods inside the intake manifold. These rods become brittle from heat cycling and eventually break, disconnecting the flap from its actuator. Symptoms include rough idle, reduced power, engine management light, and failed emissions tests. The original replacement uses the same plastic rod design and tends to fail again. Aftermarket repair kits with aluminum replacement rods are available for approximately €50-100 and are considered the permanent fix. However, total repair cost including labor for manifold removal and reinstallation runs €800-1,200 at a specialist. Carbon buildup from the crankcase ventilation system accelerates wear on these components.

The exhaust gas recirculation system on the OM642 is prone to carbon buildup, particularly on vehicles used primarily for short trips or urban driving. The EGR valve can stick open or closed, and the EGR cooler can develop internal blockages. Symptoms include rough idle, loss of power, increased emissions, and engine management warnings. Cleaning the EGR valve can temporarily resolve the issue for €200-400, but replacement of the valve and associated piping typically costs €600-1,000. The EGR cooler replacement adds approximately €400-500 to the bill. This issue is more frequent on vehicles that rarely reach sustained motorway speeds, as higher exhaust temperatures help burn off deposits.

The W222 S350d uses a selective catalytic reduction (SCR) system with AdBlue injection to meet Euro 6 emissions standards. Multiple components can fail independently: NOx sensors (€350-500 per sensor, two fitted), the AdBlue dosing injector (€300-500), and the AdBlue tank heater (€400-800 including the tank assembly in some cases). When any component fails, the car displays warnings and may eventually prevent engine start after a certain number of ignition cycles. Genuine Mercedes parts are significantly more expensive than aftermarket alternatives, and proper diagnosis is essential to avoid replacing working components. The issue typically appears after 80,000-120,000 km and is more common in vehicles used for short trips where the SCR system does not reach optimal operating temperature.

The diesel particulate filter requires periodic regeneration at sustained speeds to burn off accumulated soot. On an S-Class used primarily for short urban trips, regeneration cycles may not complete, leading to progressive clogging. Symptoms include reduced power, increased fuel consumption, and DPF warning lights. A forced regeneration at a dealer costs €150-300 and may resolve mild cases. Severe clogging may require professional cleaning (€400-800) or complete replacement (€1,500-2,500 including labor). The large-capacity S-Class engine produces less soot relative to smaller diesels, so this issue is less frequent than on compact diesel cars, but it remains a concern for urban-only driving patterns.

Some W222 owners report jerky or harsh shifts from the 9G-Tronic 9-speed automatic, particularly during low-speed maneuvers or when shifting between Drive and Reverse. In most cases this is a software calibration issue rather than a hardware fault, and a transmission control unit adaptation reset or software update resolves the problem for €150-300. In rarer cases, the mechatronic unit may need replacement at €2,000-3,000. Regular fluid and filter changes every 60,000 km help maintain smooth operation, though Mercedes officially considers the fluid to be lifetime-fill. Many independent specialists recommend against this lifetime claim and advise changes at 80,000 km intervals.

Individual glow plugs on the OM642 can fail, leading to extended cranking times and rough running when cold, particularly in winter. The glow plug control module is also a known failure point. A set of six glow plugs costs approximately €60-120, but extraction can be difficult if plugs have seized in the cylinder head, potentially adding significant labor. The glow plug relay module costs €100-150 for aftermarket or €250-300 from Mercedes. Total repair cost including labor typically runs €300-800 depending on whether any plugs are seized. This is generally a straightforward repair on the OM642 but can become expensive if a plug shears during removal.

The COMAND infotainment system in the W222 can experience software glitches including random reboots, slow response times, and complete freezing. In many cases, a system reset (holding the power button for 10 seconds) or a software update resolves the issue at minimal cost. However, if the head unit hardware is failing, replacement costs €800-1,500 for the unit plus coding and installation. This issue appears to affect a relatively small percentage of W222 owners but can be persistent and annoying when it occurs. Battery condition can also contribute to COMAND issues, as a weak 12V battery causes voltage fluctuations that affect electronic modules.