Mercedes-Benz CLS-Class (C219: 2004-2010)

Sensotronic Brake Control malfunction

From the start of production until mid-2006, the CLS-Class was fitted with a brake-by-wire system called Sensotronic Brake Control (SBC). This system caused one of the biggest Mercedes-Benz recalls.

Once the affected cars have been sorted out by the recall, the system is reasonably reliable. However, the SBC pumps on these cars have a finite lifespan, which is monitored by the car’s computer.

Once the pump reaches a fixed number of braking cycles (number of times the brake pedal is pressed) a warning light will come on. At that point, the pump needs to be replaced because it means that it has reached the end of its design life. If not replaced, the pump will eventually fail.

A new pump will cost you around £900. Reconditioned SBC pumps are also available for a smaller price.

If the SBC pump fails, a warning message is displayed on the dashboard and braking power is massively reduced – this could happen at motorway speeds. In case of pump failure, be aware that you have to apply a lot of force to the brake pedal to get the car to stop. Also, the SBC pumps occasionally fail before reaching their design lifespan.

The SBC was dropped permanently in the C219 CLS-Class and W211 E-Class because the customers lost trust in this system after the recalls. It was replaced by traditional hydraulic brakes in the middle of 2006.

In my opinion, the SBC was a failed experiment. When buying a second-hand car, it’s better to have standard hydraulic brakes that are far less complex and have been proven over decades of automotive use. They will also be much cheaper to service if anything goes wrong.

Hence my recommendation to avoid CLS-Class cars produced in 2006 and earlier. 2007 model year cars should be SBC free.

“Airmatic” air suspension

This car may be equipped with air suspension called Airmatic. The Airmatic is part of standard equipment in the CLS 500, CLS 550 and AMG models. It was an optional extra in other models – this may differ between countries.

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.

In a CLS-Class car equipped with Airmatic, the suspension is supported by four struts – 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.

M272 & M273 – soft balance shaft gears

he M272 V6 engines are equipped with a balance shaft. A balance shaft is an eccentric weighted shaft, which is used to eliminate engine vibration. It is driven by the timing chain as it needs to in sync with the engine pistons. A balance shaft is needed to make a V6 engine smooth because they are inherently unbalanced.

The M272 engines, that were manufactured between 2004 and 2008, are fitted with balance shaft gears and idler gears that can wear out prematurely.

The M273 engines don’t have balance shafts, but they still have idler gears where the balance shafts would be. These gears may be defective too. As these gears wear, the engine timing is altered due to increased slack in the timing chain.

The first indication of a problem is the “Check Engine” light and P0017 or P0016 error codes. As the sprockets continue to wear, the engine will develop a rattle from the loose timing chain. All the while, more and more metal is being ground away from the gears. If not fixed, one of the gears may fail eventually and take the engine out (valves hitting the pistons).

It is a problem that you should not ignore. The fix is to replace the gears with updated ones, which don’t wear out. It is very labour intensive, which makes it a very expensive repair.

Not all M272 and M273 engines made before 2009 are affected. Engine serial numbers below have updated gears, which are free from the problem:

• M272 engines with serial numbers higher than 2729 . . 30 468993

• M273 engines with serial numbers higher than 2739 . . 30 088611

Some engines seem to last despite having the unlucky gears, but I would not take the risk. In my opinion, affected engines are fine only as long as there is proof that the faulty gears (along with a number of other parts) have been replaced, and the engine is running well after the repair.

M272 & M273 – variable intake manifold

The intake manifold in these engines is very complex. It’s called a Variable (Length) Intake Manifold (VIM or VLIM), and it consists of three vacuum actuators, multiple levers, tumble flaps and valves that adjust the length of the intake tract.

It’s not a very reliable design with lots of plastic parts that can fail. When there’s a problem with the intake manifold, the engine performance is reduced (increased fuel consumption, loss of power, poor idle), and the “Check Engine” light may come on.

The typical cause of failure is increased friction in the mechanism from the accumulation of oil and carbon deposits in the intake manifold. Additionally, over the years the plastic parts in the mechanism become weaker and more brittle.

A couple years ago you had to buy an entire manifold assembly to fix this problem (£800 at the dealership). Luckily, there are repair kits available on the market these days, which makes this a much smaller issue.

If you are curious how carbon deposits and oil appear in the engine intake manifold – they come from the Exhaust Recirculation Valve (EGR) and Crankcase Ventilation System (CVS). These are standard systems used on virtually all road cars.

M156 engine – head bolt corrosion (CLS 63 AMG)

There have been cases of head bolt failures due to corrosion in the M156 engines. The head bolts are the fasteners that hold the cylinder heads in place. They are in constant tension to create a seal between the cylinder head and the engine block (engine block – head gasket – cylinder head).

When the bolts start corroding, the clamping force may be reduced, which could allow coolant to leak into the combustion chamber or mix with the engine oil. A typical symptom is dropping coolant level while the oil level is rising. If left untreated, the oil/coolant mix will eventually turn to sludge. Coolant entering the combustion chamber can also cause increased smoking and a rough idle.

If any of the bolts holding the cylinder heads break off, a severe head gasket leak may appear. If the leak is large enough, the coolant entering the combustion chamber has the potential to hydrolock the engine.

Hydrolock is a situation when the piston tries to compress the incompressible liquid. The liquid is not going to give in but something in the engine will – usually the connecting rods. To illustrate, here’s a photograph of a bent connecting rod after hydrolock (not from a Mercedes-Benz):

Mechanical engine damage is the worst case scenario, usually, the cars start losing coolant before failing like this.

The head bolts were eventually updated by AMG around 06.2010. All engines made before this date are affected – engines with serial numbers beyond 569xx 60 060658 have the updated bolts. Unfortunately, the production of the CLS 63 AMG stopped before AMG fixed the head bolt issue.

I recommend avoiding the CLK 63 AMG unless you can get a warranty that covers potential engine meltdown or replace the head bolts preemptively (with or without replacing the head gaskets, the latter is better but a lot more expensive).

As I see it, the percentage of engines that fail is small, but it’s not worth the risk to me.

M156 engine – camshaft wear (CLS 63 AMG)

As I see it, another weak point of the M156 engines are the camshafts, which are susceptible to premature wear. A typical symptom of a worn camshaft is ticking noise, initially only when the car is cold started. Over time, it becomes more persistent as the wear progresses.

I believe that this is caused by a combination of too soft camshaft lobes and too hard cam followers. The camshaft lobes are quite sharp (small nose radius), which may contribute to the problem. It’s not only the camshafts that can wear. Once a camshaft is scored and loses its profile, the cam followers can wear too – in severe cases to the point of breaking a hole in the centre.

If you decide to get one of these cars, listen for a ticking noise for the first couple seconds after a cold start. It’s the same procedure as checking for timing chain issues, so look out for any chain rattle too. If you hear a ticking noise, it’s likely the camshaft. If you can hear a rattle which disappears after a couple seconds, it’s most likely the timing chain. Both types of noises are a bad sign.

Also, regular oil changes are very important for camshaft life. You should avoid cars with incomplete service history.

Here’s what a worn-out camshaft looks like:

OM642 engine – oil cooler leaks

The pre-2010 OM642 engines were notorious for leaking oil from the oil cooler seals. The original seals (orange colour) weren’t able to withstand the heat and developed leaks. Updated seals (purple colour) were introduced in 2010.

There was a recall for this issue, so hopefully, most vehicles would have had the seals replaced by now. Before buying one, check if the seals have indeed been replaced and inspect the car for oil leaks.

The seals are cheap. However, their replacement is expensive as the fuel injection system and intake manifold need to be disassembled to get to the oil cooler. The oil cooler sits on top of the engine, between the cylinder banks, underneath the intake manifold. The symptoms of a leaking oil cooler are dropping oil level and oil underneath the vehicle after a longer stand still.

OM642 engine – swirl flap motor

There have been cases of swirl flap motor failures in the OM642 engines due to contamination with engine oil. The swirl flap motor is located below the turbocharger and the turbo intake tends to develop leaks in this engine. The oil leaking out from the air intake may get onto the swirl flap motor and cause it to fail.

When the swirl flap motor fails, it puts the car in limp home mode along with turning the “Check Engine” light on. The air vented from the crankcase through the PCV system contains oil vapours. The PCV breather pipe is connected to the air intake before the turbocharger – that’s how engine oil gets into the intake manifold.

Replacing the swirl flap motor is not as painful as replacing the oil cooler seals, but there is still a lot of parts in the way, and the motor itself is not that cheap.

For this reason, people came up with a way to disable the swirl flap motor using a simple resistor to trick the car’s ECU into thinking that the motor is working. This solution is cheaper than replacing the faulty motor at the cost of more pollution.

The swirl flaps are not essential for the engine to run – they are there to improve emissions and disabling them has a minimal impact on engine performance. Keep in mind that disabling emissions controlling equipment is considered illegal in most countries.

OM642 engine – Black Death

The first two generations of CDI diesel engines may develop leaks from the fuel injector seals (copper washers). When a leak occurs, the gases and the diesel fuel from the combustion chamber can escape and cover the area around the leaking injector with burnt, hard, tar-like substance.

“Black death” is a dramatic name for something relatively inexpensive to fix, provided that you catch it early. Any leaks should be visible once the plastic engine cover is removed. 

If there was a leak, you will see a black mess on top of the engine. You may also smell diesel fuel inside the car when the engine is running. If the leak is large enough, the engine may sound like a steam locomotive due to gases escaping from the combustion chamber.

If left untreated, it can become very expensive to fix – injectors seized in the cylinder head, damaged injectors seats and massive carbon build-up to clean.

Summary of problems & additional information

• The C219 (also called W219) CLS-Class is based on the W211 E-class. Therefore, it shares many parts with the E-Class. The maintenance costs should be similar for both models, despite the CLS-Class being a more expensive car.

• Most Mercedes-Benz cars, CLS-Class included, made in 2003 and onward have improved corrosion protection (galvanized body). Mercedes-Benz finally got it right. Rust was a big problem with many Mercedes-Benz vehicles produced between 1993 and 2004. The CLS-Class cars were galvanized from the start of production.

• Avoid CLS-Class cars produced in 2006 and earlier because they are equipped with Sensotronic Brake Control (SBC). 2007 model year cars should be SBC free (please check, don’t assume).

• A car with the Airmatic suspension will be significantly more expensive to service than a car with traditional suspension. Expect to do some maintenance work between 100,000 and 150,000 miles on an Airmatic car – it could be an air leak somewhere, a new air pump or a pair of struts. In my opinion, the Airmatic is not unreliable, just a lot more complex than traditional suspension.

• All C219 engines are fitted with timing chains that don’t normally have a specified replacement interval, but they will not last forever. Click here to learn more about timing chains.

• Watch out for balance shaft and idler gear issues in the M272 and M273 engines. The balance shaft horror story and the overly complex variable intake manifold mechanisms are the only real issues with these engines. Once fixed, they are not bad units. Unfortunately, Mercedes-Benz improved the balance shaft gears only in 2008. If you are going to buy a C219 with the M272 or M273 engines, be very careful not to buy one with worn gears. Look for a car that had them already replaced or one with updated gears – check engine serial number.

• The M156 was the first engine designed fully by AMG and not based on a Mercedes-Benz engine. Despite having excellent performance and winning multiple awards, this engine has its problems. I recommend avoiding the CLS 63 AMG unless you are planning to do something about the head bolts that may corrode.

• As for potential camshaft wear in the M156 engines, the safest thing to do would be to remove the valve covers and inspect the camshaft for wear before buying a second hand CLS 63 AMG. Many of these engines can reach a relatively high mileage without problems. If you are certain that the camshafts are in good shape in the car you are planning to buy, you should not have any issues for quite a while, provided that you maintain the engine well.

• The V8 M113 engine – Mercedes-Benz got this one right. It’s a reliable unit with no major flaws, unfortunately, only available in the pre-2007 C219 models that have the SBC.

• 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. Apart from oil cooler leaks and injector seal leaks (“Black Death“), the things that could go wrong with the CDI engines are typical for most Common Rail diesel engines.

• Please be aware that Mercedes-Benz is a manufacturer of high-performance luxury cars. High performance usually goes hand in hand with increased complexity. When things go wrong, you can expect the service costs to be above average.

Petrol engines – specs & performance figures

Diesel engines – specs & performance figures

Petrol engines – technical details

Diesel engines – technical details