Mercedes-Benz W221 problems: So you want an S-class, good for you. The S-Class is not only the most prominent figure on the road it was and still is the trendsetter for all that is to come. What you see featured as a novelty in an S-Class today will be present in all cars in about 20-25 years. That is how it used to be, and it still is to some extent. The W221 S-Class was a successor to the not-so-popular W221 S-Class that was plagued by a plethora of issues. The W221 hit the market with once again a unique S-Class interior and a wide selection of features and engines. Owning an S-Class does mean that you have to be ready to repair all those extravagant features and a big engine in the front. Overall, the W221 S-Class was a good Mercedes product, but as years passed, its problems revealed themselves and they can be quite the nightmare to the second, third, or even the fourth owner. Here is a breakdown of all the issues and problems plaguing the Mercedes W221 S-Class.
Mercedes-Benz W221 problems: Major issues
- W221 S-Class models with the 7G Automatic Transmission (722.9) have known issues with the Transmission Control Unit (TCU), the conductor plate and the valve body. Some problems with the transmission can result in jerky, rough gear shift while other problems can send the car into limp mode. Problems with the TCU used to be a thing that you could only solve at the dealership, which of course meant it was insanely expensive. Nowadays, their problems are all known and several companies are offering professional repairs for a fraction of the cost.
- Another component of the transmission that owners report as likely to fail is the gear selector module. The W221 S-Class does not have a mechanical connection to the transmission anymore. It uses a shift-by-wire approach that is controlled by the Intelligent Servo Module (ISM) which is prone to failure.
- The petrol versions (M272 V6, M273 V8 engine) dubbed the S350, S450 and the V8 S500 are prone to failure of the plastic actuator cam in the variable intake manifold (VIM). The symptoms include rough idling, a loss of power, and a check engine warning light on the dashboard. This failure occurs as a consequence of residue buildup coming from the PCV valve that accumulates on the plastic swirl flaps inside the variable intake manifold. The accumulated carbon increases the resistance on the plastic actuator which causes it to fail. Other parts of the VIM can fail as well.
- The same V6 and V8 petrol engines (M272 V6, M273 V8) that were produced before June 2008 may experience oil leaks around the plastic cam plugs. This plug is located on the back of the cylinder head.
- If you wish to drive a W221 with ABC suspension, make sure your wallet is ready for it. The ABC or Active Body Control suspension is insanely complex, involves a large number of sensors, hydraulic components, an ECU, and more. If anything breaks, be ready for big bills at the service center. If you still want it, go for the 2008 model years and up as they received an updated version of the ABC suspension.
- The M272 V6 and the M273 V8 engines made between 2004 and 2008 are equipped with balance shaft gears and idler gears that are made to eliminate engine vibrations. Even though the M273 does not have balance shaft gears, they still share the same faulty idler gears that will need replacement parts sooner or later. If you go for a car made in that period, make sure that this problem has been taken care of and that the engine runs well after the service.
- Nearly all of the W221 S-Classes fitted with the M276, M278 and the M157 suffer from a timing chain rattle problem. The problem was fixed by fitting non-return check valves into the oil passages that provide the timing chain tensioners with oil. If you are buying a car with these direct injection engines, make sure this repair was done. Not a thing you wish to be doing on your own.
Mercedes-Benz W221 S63 AMG and M275 V12 problems
- A weak point of the 2006-2010 W221 S63 AMG M156 engine is the premature camshaft wear. The first symptoms of this problem reveal themselves with ticking sound when the engine is cold. The sound it makes can easily be mistaken for a bad timing chain which is also not something you wish for in an AMG. Camshaft health is tightly connected to regular oil changes so make sure that the car you are buying has a transparent service history and no engine ticking noises of any kind!
- The S63 AMG M156 also suffers from a head bolt corrosion problem. Mercedes-Benz W221 problems are also present in the stronger AMG variant. The job of the head bolt is holding down the cylinder heads in their place. The constant tension they are in creates a seal between the cylinder head and the engine block. A symptom of this leak is disappearing coolant and increased engine oil level. A big enough leak can lead to engine hydro locking and cause terminal damage.
- The M275 V12 engine is only a good idea if you can afford it. Even the smallest servicing of such an engine equals big money. For instance, there is 24 spark plugs that cost almost 700$ to be replaced. These engines are known to have coil pack issues. A single-coil pack costs around 900$, you do the math.
Mercedes-Benz W221 Diesel problems: OM642 and OM651 engines
Both diesel engines listed are great workhorses for the W221 Mercedes S-Class. But just like all engines, they both come with their own set of problems.
We wrote an entire review of both: OM642 problems and OM651 problems! Check those two articles out for more detail.
OM642 (350CDI, 320CDI) problems
- Oil cooler leaks: At the bottom of the OM642 V6 diesel engines sits the oil cooler which contains two (orange) o-ring seals that were notorious for oil leaks on these engines. The material of the seals was unfit which was admitted by Mercedes-Benz. Mercedes then released an updated (violet) pair of seals in 2010 which resolved the issue. Despite the low cost of replacement parts, the entire V6 engine from top to bottom has to be disassembled in order to reach the oil cooler and these seals. If you happen to do this job, make sure you replace several other seals on the intake manifold, check the state of the intake manifold and the fuel injection system.
- The OM642 engine was also known to have issues with the swirl flap motor. The swirl flap motor can get contaminated with engine oil because it is located below the turbocharger and the turbo intake. This leak causes the swirl flap motor to fail which engages the car’s limp mode. Replacing the swirl flap motor is not an easy job, which is why people figured out a way to remove the swirl flap motor and the swirl flaps which causes slightly increased emissions but no other difference to the engine.
- Copper fuel injector seals. The famous “Black Death” fuel injector issue is an OM642 delicacy. The copper washer seals around the fuel injectors get burnt into the engine by escaping diesel fuel. They are sealed into the engine with a black and hard substance. You can notice leaky fuel injectors by observing a mess made by diesel fuel when you remove the plastic engine cover. You can also smell the diesel fuel around the engine or inside the cabin. Leaving this untreated can lead to damaged injector seats and a nasty carbon build up that is hard to clean.
OM651 250CDI engine problems
- The 250CDI OM651 engine was the first diesel Mercedes engine to feature a single-row timing chain positioned in the back of the engine. The position of the timing chain makes the access dificult and the procedure more difficult. These timing chain failures were not common but do be aware of that when looking at potential cars. Listen for any ticking, knocking sounds when the engine is cold.
Mercedes-Benz W221 problems: Minor faults
- If you have ever owned a vehicle with air suspension you know what kinds of issues you can expect. The W221 only comes with air suspension and the thing that most commonly fails is the air suspension compressor. The air compressor is a known weak point of the W221 S-class and its responsibility is major. If the air compressor fails, the car drops to the ground and it is unable to drive. However, if the car drops to the ground, there are multiple possibilities for errors. A proper diagnosis with diagnostic tools is necessary to determine the problem. Checkout out Airmatic Problems And Solutions article to learn more.
- Staying on the topic, the air suspension bags of the W221 are considered to be much more reliable than those of the predecessor, the W220. We have to warn you that in the case of high mileage vehicles, replacing air suspension bags is to be expected.
- Another component of the air suspension that is seen as a common problem is also the rear level height sensor. A failed rear height sensor is recognized by a simultaneous drop of both sides at the back. This can leave you unable to drive.
Body and interior problems
- Before you buy an S-Class with optional multi-contour seats, be aware that these seats are incredibly complex and full of potential issues. They are filled with heating pads, air bladders, wires, air hoses and a separate external air pump. The system can encounter several problems which are a pain to resolve.
- Sunroof drains are the only body problem of the W221 S-Class. Without removing the interior headliner, you are only able to clean the front drains which are not enough. Because it is such a hassle to remove the headliner we advise you to clean the back drains with a thin wire or brush.
Electronic problems
- A common electronic problem on the W221 is a failing auxiliary battery that runs all the electronic interior features and systems. The main battery is used for engine ignition and transmission control, but the auxiliary battery takes care of all the rest. Because the W221 S-Class features so many electronic features, the pressure on the auxiliary battery is big. This battery is known to fail but it is easily replaced.
- The W221 S-Class is filled with optic fibers that connect the COMAND unit to the CD changer, speakers, and navigation unit. The common problem in this loop lies at the amplifier which is responsible for the sound. When the amplifier fails, the W221 loses sound and in some cases, you wake up to a drained battery.
- Windows regulators (and in some cases also window motors) are known to fail which leaves your windows unable to move up or down. Fixing the problems requires you to remove the door panels, diagnose the issue and replace the parts with new replacements. This repair is a lot of work but the cost is bearable.
- Moisture is not a friend of electronics. In the case of W221 S-Class, moisture is a common enemy of the AC blower motor. The AC blower motor problems start off slowly, with the motor blower turning on and off randomly, and eventually it just completely dies which leaves you with no heating or air conditioning. Even though it is not a complex problem it can cost you from 600-900$.
Mercedes-Benz W221 problems: Frequently asked questions
Is the Mercedes W221 reliable?
For a 10-year-old luxury vehicle we would have to say yes, the Mercedes W221 S-Class is a reliable luxury car. If you buy a car with rich and clear service history, the W221 has the potential for being one of the best-used luxury cars on the market.
Conclusion and recommendation
We only recommend buying a luxury vehicle if you have enough money to afford a new one. That might sound insane but keep in mind that these are not cheap vehicles to buy, nor are they cheap to maintain after 10 years. If you wish to buy one, make sure that your first priority is a clear and rich maintenance record. Without that, just leave, it is not worth your nerves and wallet. If you can afford it, go for the petrol versions, the diesel variants are plagued with more issues and they need to work harder in order to keep the big body Benz moving. All the best!
Check out our other buyers’ guides here!
To learn more about the W221 Mercedes chassis, visit the W221 Wiki page.
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