Reliability of the used Mercedes-Benz S-Class W221
The Mercedes-Benz S-Class W221 was offered with a very wide range of petrol and diesel engines. While the W221 remains, overall, a durable and luxurious limousine, the crucial question for the used car buyer is: which engine to choose ? And what engine faults should be checked before purchase ?
Here is a complete guide — engine by engine — followed by a section dedicated to the balance shaft/pinion (M272/M273) fault , with symptoms, approximate repair cost and quick test to detect the problem.
Reminder: generations & practical implications
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Phase 1 (2005–2009) : first series — some parts and calibrations were improved on Phase 2.
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Phase 2 / restyling (2009–2013) : corrections, electronic optimizations and some mechanical reinforcements.
For engine reliability, if possible, choose a vehicle with a complete maintenance history and a Phase 2 if the budget allows (fewer electronic problems / completed maintenance).
Personalize and modernize your Mercedes S-Class W221
Even though the Mercedes S-Class W221 remains a symbol of luxury and comfort, some elements do show their age: sticky steering wheel buttons, an outdated multimedia system, or faded mirror caps. To give your limousine a new lease on life, we offer a selection of perfectly compatible accessories:
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New multifunction steering wheel buttons : ideal replacement when old ones are worn or sticky, with OEM design for perfect integration.
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CarPlay / Android Auto modules : transform your old COMAND system into a modern screen compatible with Waze/Google Maps navigation, Spotify, hands-free calling, etc.
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AMG look or carbon mirror caps : bring a sportier and more upscale touch to the exterior of your S-Class.
Each product is designed for plug-and-play installation , delivered free of charge, and covered by a 1-year warranty . A simple and lasting way to modernize the W221 while preserving its timeless elegance.
Gasoline engines: detailed inventory and reliability
1) S350: M272 engine — V6 3.5 / 3.0 (gasoline)
Usage: V6 versions (S350, S350 CGI depending on market).
Features: Alloy V6, variable injection technologies depending on variant.
Recurring problems:
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Balance shaft/balance shaft sprocket up to 2009 : Premature wear of the sprocket leads to slack in the timing chain, engine codes (P0016, P1200/P1208...) and noise from the timing side. This defect is known on many M272 models; it can cause misfires, a check engine light, and, eventually, camshaft timing problems if left unaddressed.
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Tensioners / timing chain : wear and noise when cold on early models.
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Oil consumption / leaks : check the seals and rocker cover.
Symptoms being tested: rattling or metallic noise on cold start on the timing side (right side of the bank), intermittent engine light, misfires.
Pre-purchase checks: listen at startup, OBD scan (look for P1200/P1208/P0016), ask for history and any gear repairs.
Estimated repair cost (order of magnitude): replacement of sprocket + chain + tensioners = high cost (major engine intervention; often engine removal depending on the workshop) — expect several thousand euros in a specialist garage.
2) S500 Phase 1: M273 — V8 5.5 (petrol)
Usage: Naturally aspirated V8s (luxury versions and some S500/S550 models).
Recurring problems:
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The sprocket linked to the balance shaft can also be affected up to 2009 (mechanically similar to the M272). The symptoms are similar: play in the timing, codes, rattling, and sometimes partial stalling.
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Oil consumption on some models and wear of ignition coils at high mileage.
Symptoms observed: same signs as for the M272 (noise, engine light, misfires), plus often higher maintenance bills.
Pre-purchase checks: same procedure as for M272; require proof of intervention if pinion replaced.
Repair estimate: high cost, comparable to the V6 depending on complexity.
3) S500 Phase 2: M278 — V8 4.7 Biturbo (petrol)
The M278 twin-turbo V8, introduced with the Phase 2 of the W221 S-Class, represents a technological leap compared to the naturally aspirated M273: direct injection, downsizing, twin-turbocharging, and revised thermal management. This engine offers an excellent compromise between power, fuel economy, and refinement .
In terms of reliability, it is considered robust if rigorously maintained, but several points warrant inspection before purchase:
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Coolant leaks at the water pump housing or plastic fittings (heat + aging)
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High-pressure injectors can become clogged over time, or poor-quality fuel can cause rough idling and trigger fault codes.
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Boost pressure sensors and wastegates : sometimes temperamental with age, risk of temporary power loss
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Intake system fouling (direct injection): cleaning recommended after high mileage
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Ignition coils and spark plugs : to be considered routine maintenance on a V8 turbo
This engine is also sensitive to excessively long oil change intervals . A clear service history with the correct oil is essential .
4) S600: M275 Engine — 5.5L V12 Biturbo
Usage: S600 (and Limousine / Guard versions depending on markets).
Features: V12 twin turbo, very high torque, demanding thermal management, numerous specific parts.
Recurring problems:
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Specific ignition coils : very expensive and can cause misfires, limp mode, vibrations.
➜ On a V12, an ignition failure can quickly become serious. -
Engine wiring harness / connectors : thermal aging due to turbocharger heat → possible electrical anomalies.
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Cooling system : heat exchangers / hoses / water pump to be monitored; overheating can cause major damage.
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Oil leaks : cylinder head covers, various seals → long hours of labor due to reduced accessibility.
Diesel engines: detailed inventory and reliability
4) S320 and S350 CDI: OM642 engine — 3.0 V6 Diesel
Advantages: excellent torque, very good longevity if maintained; widespread and well-understood engine.
Known weaknesses:
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Oil leaks at the oil-cooler O-rings can be costly to repair if neglected.
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EGR / EGR valve and fouling : symptoms of power loss, smoke, need for cleaning.
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DPF / FAP : problems if used intensively in urban areas (failed regenerations).
Symptoms being tested: abnormal smoke, loss of power, DPF/EGR warning lights.
Recommended maintenance: regular motorway journeys, injector checks, oil and filter changes according to manufacturer's frequency.
Lifespan: many OM642s exceed 200k–300k km if well maintained.
S420 CDI: OM629 engine — V8 4.0 Diesel Biturbo
Usage: High-end V8 diesel versions (S420 CDI then S450 CDI in some markets).
Features: High torque engine, 2 turbochargers, high injection pressure, high performance with low fuel consumption for its size.
Recurring problems observed:
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Injectors and injector seats
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Rattling noises, diesel smell, black deposits ("black death")
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Delaying intervention can damage the cylinder head
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DPF / Sensors / EGR Valve
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Risk of clogging if mostly driven in urban areas
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Check engine light, loss of power, increased fuel consumption
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Timing chain and tensioners
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Possible wear over high mileage, noises when cold, and synchro misalignment.
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Turbochargers
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Check for fouling of variable geometry components and leaks in air/oil circuits.
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Symptoms: turbo lag, limp mode, smoke
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Cooling
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Auxiliary radiators + hoses + water pump → sensitive to the age and thermal weight of the V8 diesel engine
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Associated 7G-Tronic (722.9) Box
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An oil change is mandatory every 60,000 km to prevent slippage/jerks or TCU failures
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Cross-cutting problems related to engine groups (petrol + diesel)
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Local overheating / cooling circuits : water pump, thermostat, hoses — check history.
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Ignition systems (petrol) : coils / spark plugs to be replaced routinely, monitor for misfires.
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Injection & high pressure systems (diesel) : leaking or worn injectors → loss of performance.
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Clutches / gearboxes (if sporty / manual versions) : on automatic gearboxes, regular oil changes are essential.
Balance shaft / balance shaft pinion (M272 / M273) — complete file (must be read)
What is this ?
On some Mercedes V6/V8 engines (M272/M273), a balance shaft/idler gear —or the entire balance shaft assembly—was manufactured with an inadequate surface treatment: the teeth wear prematurely under the stress of the timing chain. When the teeth wear, play develops, causing the chain to loosen, resulting in timing issues on the right bank, camshaft codes, and timing problems.
Common symptoms (essential to know)
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A metallic rattling sound can be heard on the timing side, especially when starting from cold.
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Engine warning light with codes such as P0016 , P1200 , P1208 or errors related to timing.
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Risk of failures / irregular operation , or even loss of synchronization if the degradation progresses.
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In the worst cases, there is a risk of damage to the camshafts or other distribution components.
Why is this important on the W221?
Many W221s with M272/M273 engines had this fitted at the factory: these engines have experienced cases of worn pinion gears as early as 30–80k km for some examples; others last longer — variability exists — but the failure is widespread enough to make it a systematic point of check during a pre-purchase inspection.
Quick diagnosis (what you can do)
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Listen : turn the engine on / start from cold and listen carefully on the timing side (passenger side on many models); a clunk/click-click should alert you.
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OBD scanner : search for timing codes (P0016, P1200, P1208…).
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Check history : ask for invoices showing sprocket/chain/tensioner changes.
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Visual inspection by a professional : a Mercedes workshop or specialist can check for play and wear via the timing cover (often requiring partial disassembly).
Cost & complexity of the repair
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Major intervention : replacement often requires removal of the engine or significant operations (depending on the workshop).
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Cost : varies depending on the country and workshop, but expect to pay several thousand euros (four figures) for the chain, sprocket(s), tensioners, and labor. Some operations can cost €4,000–€6,000 or more if parts/time are involved.
Preventive tip
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Check your VIN and any recalls/technical bulletins with Mercedes; some batches have undergone corrective actions. Request proof of intervention if your vehicle is within the affected period.
Which engine should you choose? Practical recommendations
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If you do a lot of motorway driving : choose the OM642 (3.0 CDI) — robust and long-lasting if maintenance is kept up.
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If you want reasonable fuel economy : choose post-facelift (ph2) V6/V8 or versions with a history showing preventative replacement of timing components.
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Avoid : M272/M273 V6 engines prior to 2009 with no service history or with indicated symptoms (noises/codes), unless you are prepared to finance a major repair.
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AMG / V12 : extreme sensations, but much higher maintenance budget — reserved for enthusiasts.
Engine checklist for the visit/test (quick summary)
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Cold start → listen for any abnormal noise (click-click).
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OBD scanner → search for P0016, P1200, P1208, camshaft codes, DPF/EGR, rail pressure etc.
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Check invoice history (chain, sprocket, tensioners, injectors, gearbox oil changes).
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Visual inspection underneath → traces of oil, water pump leaks, injector leaks.
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Dynamic test → cut-outs, jerks, loss of power.
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For diesel → DPF regeneration test under load (highway) and EGR/valve status.
