Mercedes-Benz S-Class (W220: 1998-2005)

Corrosion (water-based paint)

Rust was one of the top problems with Mercedes-Benz vehicles produced between 1993 and 2004.

This is because around 1993, Mercedes-Benz implemented a more environmentally friendly, water-based paint. Coupled with steel that isn’t very corrosion resistant and no galvanizing process, most W220 models are very susceptible to corrosion.

Mercedes-Benz eventually started galvanizing their cars, which improved the corrosion resistance significantly. In the case of W220 S-Class cars, they became galvanized from the beginning of 2003.

Therefore, if you are planning to buy a W220, look for a car produced in late 2003 or later. It will have much better corrosion resistance, which is important if you are planning to keep the car for a few years.

Here’s why good corrosion protection is important:

Airmatic suspension failure

All W220 S-Class cars are equipped with air suspension called Airmatic. The Airmatic is part of standard equipment unless the car has the optional Active Body Control suspension (ABC).

The ABC is a hydro-pneumatic suspension, and you can check if any particular W220 has ABC by decoding the VIN number. The option code for ABC is 487. Also, all V12 and AMG models had ABC as standard instead of Airmatic.

Air suspension is commonly used in trucks and buses because vehicles with air suspension can maintain correct height and level despite the load. Have you ever seen a bus tilt and soon after level out when the passengers get off at the bus stop? That’s air suspension reacting to new conditions.

The air suspension in Mercedes-Benz cars can react in the same way, and it’s capable of changing the ride height and damping stiffness. The Airmatic ride quality is indeed very good.

Instead of traditional coil springs and dampers, the Mercedes-Benz W220 is fitted with four Airmatic struts, which are air springs and dampers integrated into single units.

 

Here’s how the Airmatic is different from traditional spring suspension:

Traditional suspension

• four springs – they support the car and allow suspension movement (suspension travel)

• four shock absorbers – they dampen the spring oscillations and prevent excessive suspension movement (bouncing)

Airmatic

• air pump (generates air pressure for the entire system)

• air reservoir (stores compressed air)

• ride height sensors (they measure the ride height)

• valve body (distributes air to the air springs)

• four struts (shock absorber and air spring in one)

• air lines that connect all of the above

In my opinion, the Airmatic is not unreliable, but it is significantly more complex than traditional suspension.

Some people got burned by trying to fix their Airmatic suspensions at a Mercedes-Benz dealership. The prices at the dealership can be high when it comes to sorting out Airmatic issues, and the typical dealership approach is to keep replacing components until the problem is fixed, without actually trying to locate the exact failure point.

The parts can be expensive but most things, like struts or the air pump, are easy to replace. In my opinion, you will be happy with the Airmatic suspension provided that you learn how the system works, and how to diagnose problems yourself, so you don’t get ripped off when something starts leaking or stops working.

Also, be aware that if some critical components in the Airmatic fail, for example, the air pump, the car will become undrivable.

There are multiple options available on the market today that can help you save money servicing the Airmatic suspension:

• compressor repair kits

• aftermarket parts (Arnott has a good reputation)

• reconditioned parts

• coil spring conversion kits (not recommended)

 

When checking the Airmatic suspension, look out for the following symptoms of malfunction:

• air compressor running too loud (worn out)

• compressor turning on too often (air leak)

• Airmatic fault messages when the car is cornering or braking hard

• the car taking too long to raise from lowest position (air leak or worn out air pump)

• cracked dust covers on the struts (any damage there will massively accelerate the wear by allowing dirt and moisture in)

• oil leaks at the bottom of the struts (leaking shock absorbers)

• check that the car responds quickly to manually adjusting the height with no warning messages

• car dropping too quickly – on one corner or more than one

Check the car after it has been standing still overnight – it should not be on the ground. A little bit of pressure may escape, but the car should stay up and level.

A system in good condition should be able to hold air for a couple days easily. If it drops in a couple hours, something is worn out or there is a significant leak somewhere. If the car drops too low to drive, “Car too low” message will appear on the dashboard – it’s a bad sign.

Driving with air leaks will prematurely kill the air pump because then it has to turn on more often to replace the escaping air. If you are going to buy a car that has a leaking system, expect the air pump to be on its way out too.

ABC suspension failure

The Mercedes-Benz W220 may be equipped with hydro-pneumatic suspension called Active Body Control (ABC). The ABC is standard equipment in the S 600 and AMG models (S 55, S 63, S 65). It was an optional extra in other models.

The Mercedes-Benz’ hydro-pneumatic suspension has some similarities to the suspension Citroen cars were famous for. When it works, the ABC exceeds what standard coil spring suspension can do. It is also better than the Airmatic suspension when it comes to handling.

The ABC suspension is very comfortable, and at the same time, there is very little body roll when cornering or braking (hence the word “Active” in the name). The system can adjust its position up to 5 times per second (5 hertz). Also, it is self-levelling, which means that it will maintain the ride height despite the load in the car.

If you think the Airmatic suspension is complex, never buy a car with the ABC suspension. The ABC is a lot more advanced than the Airmatic, let alone a standard suspension. Thus, you can expect the maintenance costs to be accordingly higher.

 

Here’s how the ABC is different from coil spring suspension:

Traditional suspension

• four springs – they support the car and allow suspension movement (suspension travel)

• four shock absorbers – they dampen the spring oscillations and prevent excessive suspension movement (bouncing)

 

Active Body Control

• hydraulic piston pump (generates pressure for the entire system)

• oil reservoir (stores hydraulic oil)

• two valve blocks – one per car axle

• four struts (the strut is a coil spring, a shock absorber and a hydraulic actuator integrated into one unit)

• two pressure accumulators (nitrogen spheres) – one per car axle

• pulsation damper and return accumulator (two more nitrogen spheres)

• ECU (the brain of the system)

• hydraulic hoses that connect all of the above

• over a dozen electronic sensors

 

Let me try to briefly explain how this system works:

The suspension struts contain a regular coil spring and a shock absorber – just like in a typical car. Additionally, there is a hydraulic cylinder in each strut that can change the height of the suspension (each wheel individually).

The system is powered by a hydraulic pump, monitored by sensors and controlled using solenoid valves. This allows for real-time adjustments to ride height and vehicle body lean, for example during cornering or braking.

There are four pressure accumulators that have a membrane inside and pressurized nitrogen gas behind it. The membrane is flexible. On one side of the membrane there is gas and on the other, there is hydraulic fluid. The membrane can deflect to store energy (pressure) because nitrogen gas is compressible.

There are two accumulators that store the pressure to feed the system as explained above. The other two are there to dampen pressure spikes in the system. The hydraulic pump is a piston pump so it generates pressure pulses with every stroke. The pulsation damper, which is just another nitrogen accumulator, evens out these pulses (membrane deflecting). The return accumulator does a similar job after the oil leaves the struts.

The ABC is really a conventional coil spring suspension with added hydraulic levelling. It’s the coil spring inside the struts that does the job of absorbing the shocks from the road, and the hydraulic system is there just to adjust the car body lean and height.

If you compare the ABC to other hydro-pneumatic suspension setups:

• In the Mercedes-Benz R129 SL-Class, the ADS suspension has conventional coil springs but no conventional shock absorbers. The hydraulic accumulators serve the function of the shock absorbers. The gas behind the membrane inside the nitrogen sphere is compressible and can absorb the shocks from the road (membrane deflects).

• In older Citroen cars, which were famous for their hydro-pneumatic suspensions, there is a nitrogen sphere at each wheel that serves the function of both the shock absorber and the spring. You won’t find any coil springs in Citroen cars with hydro-pneumatic suspension, and when a nitrogen sphere fails, there is virtually no damping in a Citroen car.

Similarly, the damping is lost when an accumulator fails in the R129 SL-Class with the ADS suspension. Citroen just took it one step further by getting rid of the coil springs altogether.

I hope I made this clear enough…

 

Here’s a video of an accumulator taken apart. It’s not from an ABC car, but its construction is the same.

 

Anyway, the key points are:

• The ABC is a complex, high-performance system and it will be more expensive to maintain than standard suspension or even the Airmatic.

• The ABC was improved in 2007, which is after the production of the Mercedes-Benz W220 stopped, unfortunately. The second-generation ABC was introduced in the W221 S-Class and the R230 SL-Class.

• The age of the vehicle is important – the rubber hoses and seals age, which increases the likelihood of failure. The hydraulic hoses deteriorate and have a finite lifespan (they can burst). If a hose blows, the suspension shuts down. If you don’t stop on time, the hydraulic pump may die from running dry. As you can see, it’s important to keep the hydraulic hoses in good condition.

• The nitrogen spheres last around 60k miles or 10 years, whichever comes first. They are service items and will need to be replaced regularly. Even if you don’t drive the car, the nitrogen gas will eventually escape, just like air escapes from a seemingly airtight balloon.

• The hydraulic pump will need replacing at some point (very expensive). The pump has two sections – one that powers the suspension, the other runs the power steering.

• There are some options available on the market today that can help you save money servicing the ABC suspension: repair kits, aftermarket parts (Arnott has a good reputation) and reconditioned parts. Please be aware that it’s still going to be expensive…

 

If you’re still convinced that you want an S-Class car with the ABC suspension, here’s what to look out for:

• Car dropping to quickly (on one corner or more than one) – visually check the car after it has been standing still for a couple days – the chassis should not be on the ground. According to Mercedes-Benz, a system in good working order should be able to hold the oil pressure at least for one week. If the car drops earlier, something is wrong with the valve block or there is a leak somewhere (probably a strut).

• Any ABC warning messages, appearing for a couple seconds when cornering, braking or after hitting a pothole, are bad signs. Before buying a car with the ABC, I recommend taking it to a professional to check the diagnostics log for any stored errors.

• Check the hydraulic fluid – it should be green. If it’s dark brown, black or the fluid level is too low, it means the car has been neglected or maintained poorly. Do not buy such a vehicle. Running the hydraulic pump without oil will kill it very quickly. The dark colour of the fluid means that it is dirty and full of abrasive particles – the entire hydraulic system could be worn out.

• Also, do not buy a car without maintenance history (including filter and hydraulic fluid replacements).

• Check the struts and the underside of the car for any oil leaks. Watch out for cracked dust covers on the struts (any damage there will accelerate the wear by allowing dirt and moisture in).

• Check that the car responds correctly, with no warning messages, to manually adjusting the ride height.

• Humming or howling noise between idle and 2000 RPM means that the pulsation damper has failed.

• The ride should be smooth and at the same time, there should be very little body lean when cornering or braking. If the car feels bouncy or hard, something is wrong.

M137 & M275 engine –  high maintenance costs

The V12 engines fill out the engine bay completely, so replacing parts can be a nightmare. Something as simple as changing the motor mounts may require the engine to be removed from the car. It is possible to do it with the engine in the car if you get creative, but my point is that even small repairs can be pretty expensive.

There are 24 spark plugs and two ignition coil packs in the M137 and M275 engines – one coil pack per cylinder bank. Each coil pack is an integrated unit that provides ignition for 6 cylinders.

Imagine that you’re trying to fix a rough idle or misfire in the M275 V12 engine. Replacing the spark plugs alone will cost £500 or more because it’s not as straightforward as in an average engine and because there is 24 of them.

The coil packs fail occasionally and sometimes when there’s a misfire, replacing the spark plugs alone might not be enough. So you’ve already spent a lot of money on the spark plugs, and now you’ll try replacing the coil packs…

… a single coil pack is around £800.

The M275 is not a bad engine at all, but as you can see, parts aren’t cheap.

Now, the M137 is on a yet another level of expensive. Just so you know, this engine has six catalytic converters and eight oxygen sensors!

I hope this gives you an idea what you’re getting yourself into when you buy a second-hand, V12 Mercedes-Benz W220 – especially one with the M137 engine.

M137 engine – oil cooler leak

There have been cases of the M137 engines developing leaks from the oil cooler that sits on top of the engine between the cylinder heads.

In my opinion, the oil cooler leaks are a fairly common problem in these engines, and the amount of oil that leaks out can be significant. So, it’s not an issue that you can ignore.

The problem is that in order to replace the oil cooler seal, you need to remove both cylinder heads. Need I say more?

OM628 engine – timing chain problems

There have been cases of people having problems with the timing chain stretch in the OM628 engines. It’s not a common engine so there isn’t much information out there, but apparently, the chain tensioner and one of the slide rails were updated in 2002 to prevent the chain from skipping teeth (updated tensioner part number is A6280500311, while the original was A6280500011).

If you are looking for a car with the V8 diesel engine, I recommend getting one that was produced in 2003 or later. Additionally, pay extra attention to any unwanted chain noises and avoid high mileage cars.

The first symptom of any chain or chain tensioner problems is usually a timing chain rattle after a cold start.

Summary of problems & additional information

• In traditional Mercedes-Benz fashion, the W220 S-Class was available in short and long wheelbase versions.

• The Airmatic air suspension was standard equipment in the Mercedes-Benz W220 S-Class, except for the S 600 and AMG models, which have the ABC hydro-pneumatic suspension. In other models, the ABC was an optional extra (option code 487). Both types of suspension are expensive to maintain, with the ABC being the more expensive of the two.

• The main problems with the Mercedes-Benz W220 are related to the complex suspension (Airmatic or ABC), rust and electrical gremlins (especially the pre-facelift cars). On the other hand, the M112 (V6) and M113 (V8) engines are reliable.

• Corrosion was a big problem with the W220 and other Mercedes-Benz cars from those years. Mercedes-Benz eventually started galvanizing the W220 in 2003. Those cars have much better corrosion protection.

• You should avoid pre-facelift cars because of build quality problems, corrosion and a slightly less reliable Airmatic suspension (updated later). My recommendation is to only consider late 2003 and newer models, which have all the initial problems worked out. The post-facelift, twin-turbo V12 engines are better too.

• The V12 W220 models are very expensive to maintain. Pick your model wisely – there will be a huge difference in maintenance costs between an S 320 and an S 600. If you are hell-bent on getting a V12 Benz, get a post-facelift model with the M275 engine instead of the older M137. The W220 cars with the M137 engine can be extremely expensive to maintain.

• Please be aware that Mercedes-Benz is a manufacturer of high-performance, luxury cars. High performance usually goes hand in hand with increased complexity. This is particularly true for the S-Class, which has been Mercedes-Benz’ testbed for the latest technologies. The features you see in an S-class car today may be popular in more ordinary cars in a few years. When things go wrong, you can expect the service costs to be above average.

• All engines in the Mercedes-Benz W220 are fitted with timing chains, which normally don’t have a specified replacement interval. The timing chains in the W220 are generally reliable, with the exception of the early OM628 engines, but they will not last forever. Read more about timing chains here.

• Click here for an article that might help you decide if a modern diesel engine, like the Mercedes-Benz CDI, is the right choice for you. Some OM648 diesel engines in the W220 may have a diesel particulate filter (DPF). Before buying a particular car, you can check if it has a DPF by decoding the Vehicle Identification Number (VIN). The DPF is marked as option 474.

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Diesel engines – specs & performance figures

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Diesel engines – technical details