Flagship luxury sedan offering exceptional comfort and technology. The M278 twin-turbo V8 is generally reliable when maintained, with many reaching 200,000+ km. Main concerns: timing chain tensioners on early engines (check engine number), AIRMATIC suspension wear around 80,000-100,000 km, and expensive electrical issues like headlight water damage (€2,800 per unit). Pre-facelift 2014-2016 models have more issues, especially 7G-Tronic transmission rough shifting. Avoid first-year 2014 models if possible. This is a complex, technology-heavy car requiring deep pockets for repairs.
AIRMATIC air suspension strut failure€1,200 - €2,500 per corner
Air struts leak or fail between 80,000-100,000 km, often affecting multiple corners · more· less
The W222 AIRMATIC system is known to develop air leaks as the rubber components age and become brittle. Average lifespan is 80,000-100,000 km depending on driving conditions. Dealer replacement costs €1,200-€2,500 per strut depending on front/rear. For balance and performance, both struts on the same axle should be replaced together (€2,400-€5,000 total). Independent shops using Arnott aftermarket struts can save 40-50%. Some owners convert to coil springs (€1,500-€2,500 for full system) to eliminate future air suspension costs.
Early engines lack check valves causing cold-start rattle; can lead to catastrophic damage if ignored · more· less
Early M278 engines (up to engine number 278 9xx 30 073273) require installation of check valves and updated tensioners. Engines from 278 9xx 30 073274 to 278 9xx 30 103675 (Feb 2013) need only check valves. Engines ending in 30 191844 or higher have enhanced components. Symptoms: 1-30 second rattle on cold start as tensioner loses oil pressure overnight. The M278 has complex timing (1 primary chain + 2 secondary chains, 3 tensioners total). If rattle persists, chains, guides, tensioners, and sprockets all need replacement. Labor is 7-48 hours depending on method - dealers pull entire engine (€6,000+), specialists can do it in-car (€1,500-€2,500). Verify engine number before purchase.
Headlight water damage and fogging€2,800 - €4,500 per unit
LED headlights develop moisture intrusion causing internal electronics failure · more· less
This is a notorious W222 design flaw. The LED headlights run cool (unlike older halogen bulbs) and have internal fans, but the design allows moisture buildup. Water damages the ballast and control units, requiring complete headlight assembly replacement at €2,800-€4,500 per unit. Mercedes issued bulletins for desiccant packs (parts A0008261300/A0008261200, 30-min installation), but this is only a temporary fix lasting 5-6 months. One UK owner paid £1,800 every 5 months for new units. After warranty expires, there's no cost-effective permanent repair. Critical: inspect headlights carefully before purchase - any fogging indicates impending €5,000+ repair bill.
Turbocharger failure (M278 engine)€2,500 - €8,000
Twin turbos fail from oil contamination, wastegate issues, or coolant line leaks · more· less
The M278 uses twin turbochargers (one per cylinder bank). Common failures: worn bearings, oil seal leaks, wastegate actuator sticking, brittle coolant lines cracking. Symptoms include reduced power, excessive exhaust smoke, high-pitched whining during acceleration. Dealer cost: €4,590 per turbo + 16.8 hours labor (€8,000 total) because engine must be removed. Independent specialists charge €2,500-€4,000 total using remanufactured turbos. Prevention: use correct oil (5W-40 MB 229.5 spec), change every 5,000-7,500 km for turbo longevity, avoid only short trips which cause carbon buildup and actuator sticking.
Transmission wiring harness damage€800 - €2,500
Heat from exhaust damages wiring, causing transmission to refuse park or drop to neutral while driving · more· less
The W222's transmission wiring harness is positioned too close to the hot exhaust system. Heat causes insulation damage, leading to erratic transmission behavior: jittery shifts, delayed engagement, refusal to shift into park, or complete loss of gear engagement (car drops to neutral while driving). This was so widespread Mercedes issued a recall for virtually all S350 models. Check if any W222 you're considering has had this recall completed. Repair involves rerouting or replacing the harness (€800-€2,500 depending on damage extent). This primarily affects pre-facelift 2014-2016 models.
Pre-facelift models (2014-2016) with 7G-Tronic require forced adaptation; 9G-Tronic from 2017 is better · more· less
Rough shifting is extremely common on pre-facelift W222 models with the 7G-Tronic transmission (all pre-facelift years except MY2017). 9 out of 10 cases need "Forced Adaptation" or "shift normalization" - a software procedure dealers perform (€150-€300). This resets transmission adaptive learning. If forced adaptation doesn't fix it, transmission fluid service may help (€400-€800). Severe cases require valve body replacement (€2,500-€3,500). The 9G-Tronic transmission that appeared around 2015-2017 has fewer issues. Strongly recommend test-driving any pre-facelift W222 for minimum 20 minutes to feel transmission behavior at operating temperature.
Battery drain / parasitic draw€300 - €1,500
Complex electronics cause battery drain within 7-10 days; modules fail to enter sleep mode · more· less
The W222 is notorious for battery drain. The car's numerous electronic modules (infotainment, security, GPS, SAM modules, memory seats, Comand, overhead control) consume power in standby. If any module fails to enter sleep mode, battery dies within 7-10 days. Common culprits: signal acquisition module (SAM), faulty CAN bus devices, ignition switch staying partially on. Mercedes admits this defect affects 2004-2022 models per NHTSA reports. Solutions: 1) Fix root cause (€300-€1,500 depending on which module), 2) Keep car on CTEK trickle charger when not driven for 3+ days. This car demands regular driving or permanent battery tender connection. Expect battery replacement every 2-3 years (€200-€400).
M278 camshaft sensors leak oil into wiring harnesses; if it reaches ECU, €10,000+ repair · more· less
The M278 has an inherent design flaw: oil seeps from camshaft position sensors and solenoid adjuster magnets into the wiring harnesses leading to the ECU. If oil infiltrates the ECU, expect a €10,000+ bill for complete engine harness replacement. Early intervention: replacing the 4 magnets, sensors, and installing sacrificial extension harnesses costs €460-€800 at independent shops. The extension harnesses move connectors higher, preventing oil from flowing into main harness and allowing leakage detection before ECU damage. Prevention: change oil every 4,000-5,000 km to prevent sludge buildup in magnets (factory 10,000 km interval too long). Consider this preventative repair around 60,000-80,000 km.
Coolant system leaks (heater valve, intercooler lines)€60 - €1,200
Multiple coolant leak points: heater control valve, plastic intercooler lines, radiator · more· less
Common W222 M278 coolant leaks: 1) Heater control valve (MB part 2308300084) behind firewall - shows as crusted pink dried coolant, €60 part + 2 hours labor (€200-€350 total). 2) Intercooler coolant circuit: M278 has separate intercooler system with own reservoir, plastic lines running behind engine prone to leaking, no sensor to warn you (€400-€800 repair). 3) Radiator: plastic components crack from heat cycles, rubber hoses degrade (€400-€1,200 for radiator replacement). Regular visual inspection essential - check for coolant puddles, smell sweet odor, watch coolant level. Using proper coolant (MB spec, not cheap generic) prevents corrosion.
Oil consumption / valve seal wear€1,500 - €10,000
Early M278 engines suffer piston scuffing and valve seal issues causing high oil consumption · more· less
Early M278 engines had piston scuffing issues due to problematic Silitec cylinder liner coating - "total disaster" according to specialists. Later engines switched to NanoSlide coating with better wear resistance. Symptoms: burning oil between service intervals (more than 1L per 2,000 km), blue smoke on startup, misfires. Causes: worn piston rings, valve stem seals, cylinder wall scoring. Diagnosis: compression test (wet vs dry). Minor valve seal replacement requires head removal (€3,000-€5,000 without warranty, over €10,000 at dealer). Severe cylinder scoring needs rebore and new pistons (€8,000-€10,000+). Prevention: regular oil changes (5,000 km intervals), quality 5W-40 oil meeting MB 229.5 spec, avoid extended idling.
PRE-SAFE system errors / seatbelt tensioner issues€0 - €1,500
Known W222 fault; Mercedes issued recalls for seatbelt tensioners · more· less
The PRE-SAFE system is a known W222 fault. Mercedes issued two recalls for improperly calibrated seatbelt tensioners on driver and front passenger seats. Symptoms: "PRE-SAFE functions limited" warning, malfunctioning sensors, poor wiring connections, low battery voltage, faulty ABS modules, damaged brake lights. Some cases resolved with software update (covered under recall). Others require ETR belt tensioner replacement (€800-€1,500). First step: verify with Mercedes dealer if your VIN has outstanding recalls - recall repairs are free. If not covered, diagnose with Mercedes Star system before replacing parts.
Complex luxury car with expensive repairs
The W222 S500 offers incredible luxury and the M278 engine is generally reliable with proper maintenance, but this is an expensive car to own. AIRMATIC suspension, headlight water damage, and electrical issues are common four-figure repairs. Pre-facelift 2014-2016 models have more problems than 2017+ facelift versions. Avoid 2014 first-year models entirely. Budget €3,000-€5,000 annually for maintenance and repairs, potentially more if AIRMATIC or turbos fail. Only consider if you have deep pockets or excellent extended warranty.
Pre-Purchase Inspection Checklist
General checks
Complete service history Essential to verify Mercedes dealer or authorized specialist maintenance records. Look for transmission fluid changes every 40,000 km, oil changes no longer than 10,000 km intervals (shorter is better for turbos).
Tires condition and age 19-20 inch premium tires cost €350-€500 each. Check tread depth (minimum 3mm), date codes (max 6 years old), uneven wear patterns indicating suspension issues.
Cold start test CRITICAL: Start engine completely cold. Listen for timing chain rattle in first 30 seconds. Any rattle over 3-5 seconds indicates timing chain tensioner issues (€1,500-€6,500 repair).
Extended test drive Minimum 30 minutes including highway speeds to get transmission fully warmed up. Pre-facelift 7G-Tronic transmission issues only appear when hot.
Check all electronic systems Test every button, screen, camera, sensor. Electrical gremlins are expensive to diagnose and repair on W222.
Specific for this vehicle
Verify M278 engine number Check engine number stamped on block. If below 278 9xx 30 073273, timing chain tensioners and check valves need updating. If 278 9xx 30 073274 to 30 103675, only check valves needed. Engines ending 30 191844+ are enhanced. This is critical - bring flashlight and write down the full number.
Inspect all 4 headlights thoroughly Any fogging, condensation, or moisture visible inside lenses indicates impending €2,800-€4,500 per unit failure. This is non-negotiable - walk away if any moisture present.
AIRMATIC suspension operation With engine running, check ride height adjusts properly. Listen for compressor running excessively. Inspect all 4 air struts for oil/air leaking at bellows. Car should not sag overnight when parked. Press each corner - should return smoothly without bouncing.
Transmission shifting quality (pre-facelift) If 2014-2016 model, drive minimum 20 minutes until fully warm. Feel for harsh shifts, hesitation, slipping. 7G-Tronic rough shifting affects 90% of pre-facelift cars. Ask if forced adaptation has been performed - if not, budget €150-€300 immediately.
Battery condition and drain test Ask owner if car sits for 7+ days regularly. If battery frequently dies, parasitic draw issue present (€300-€1,500 to diagnose/fix). Check battery date - should be replaced every 2-3 years (€200-€400).
Oil consumption history Ask owner about oil consumption between services. Any car requiring more than 1L between 10,000 km services has worn piston rings or valve seals (€3,000-€10,000 repair). Check dipstick - oil should be clean, at proper level.
Coolant system inspection Check coolant reservoir level and color (should be pink/orange, not brown/rusty). Look behind firewall and under engine for dried pink coolant crusting indicating heater valve leak. Check for sweet coolant smell after drive.
Verify transmission wiring harness recall completed This recall affects virtually all W222 models. Contact Mercedes with VIN to confirm completion. If not done, insist seller completes before purchase - free at dealer.
Turbo operation test During test drive, accelerate hard from 2,000 RPM. Turbos should spool smoothly without excessive noise, smoke, or hesitation. Listen for high-pitched whining indicating bearing wear. Check engine bay after drive for any oil around turbo areas.
Seatbelt tensioners (driver & front passenger)Two separate recalls issued
PRE-SAFE system errorsMultiple TSBs, check VIN
Front seat belt anchor fitting (2014 S 550)Recalled Nov 2013
Engine control unit software (2014 S 63 AMG, 2015-2016 S 63 AMG 4Matic)Recalled Oct 2015
M278 timing chain tensioners (early engines)TSB issued, verify engine number
Contact Mercedes-Benz with the VIN to verify all recalls and TSBs have been completed before purchase. The transmission wiring harness and timing chain TSBs are particularly important. Recall repairs are performed at no cost to the owner.
Warranty Status
Factory warranty (2 years)Expired on all W222 S500s
Extended Mercedes warrantyAvailable, costs vary by age/mileage
AIRMATIC suspensionTypically not covered by extended warranties
All 2014-2017 W222 S500s are outside their original factory warranty. Extended warranties are available through Mercedes dealers but read the fine print carefully - many exclude AIRMATIC suspension, oil leaks, and wear items. Given the W222's complexity and repair costs, a comprehensive extended warranty from a reputable provider is highly recommended if you can find one that covers electronics and suspension.
This report is for informational purposes only and does not constitute professional advice. Estimates may be inaccurate. Always have a qualified specialist inspect the vehicle before purchase. We accept no liability for decisions made based on this information.