Mercedes-Benz C-Class (W203: 2000-2007)

Build quality issues

In my opinion, the W203 C-class cars manufactured in the first years after the model was released are considered to be less reliable than the ones made after the facelift in 2004. There is nothing terribly wrong with the pre-facelift models but there were cases of electrical issues and problems with build quality.

This isn’t unusual. Often, newly released products have some problems. It takes a while for the manufacturers to sort out design flaws and quality issues. This is true not only for cars but many other products. A bit of an extreme example is the Samsung Galaxy Note 7 with its batteries catching fire.

Corrosion (water-based paint)

In my opinion, corrosion 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.

Only in 2003/2004, Mercedes-Benz started galvanizing their cars, which improved the corrosion resistance significantly. Therefore, I recommend getting one of the post-facelift W203 models as they all have galvanized bodies. The facelift took place in 2004 (2005 in the US).

Valeo radiators & transmission failure

The early W203 models, manufactured before 09.2003, might have been fitted with radiators that can cause expensive automatic transmission failures.

The transmission oil cooler in these cars is integrated with the radiator. The faulty radiators were made by Valeo and had a problem with an internal seal that was supposed to separate the coolant from the transmission oil.

A failed seal would release the coolant into the transmission oil circuit. This oil/coolant mixture can ruin the transmission if not flushed quickly. Cars with manual transmissions are not affected.

The coolant in the transmission is not a good thing and causes severe clutch surface wear, among other issues. The fix for a transmission contaminated with coolant is to:

1. replace the transmission (expensive)

2. rebuild the transmission (also expensive)

3. if the contamination was stopped quickly enough, a transmission flush and new transmission fluid may be enough (not that expensive)

The typical symptoms of a failing radiator seal are harsh gear changes and humming/droning noise during light acceleration up to 2500 RPM. Definitely look out for this when test driving a W203 C-class made before 09.2003.

The majority of the C-Class vehicles on the road today would have had the faulty radiators replaced by now. If you do buy a car with a Valeo radiator, consider having it replaced as there is still a small risk that it could fail. It’s much cheaper to replace a radiator as a precaution than it is to replace a dead transmission.

Only cars manufactured before 09.2003 are affected and newer Valeo radiators are fine.

You can identify a Valeo radiator by the crimping method i.e. how the metal core is joined with the plastic sides. Here’s what it looks like:

M111 engine – head gasket failure

In my opinion, the head gasket is the weak point of these engines. Considering head gasket replacement is inevitable at some point, often around 150k miles.

Before the gasket fails completely, these engines often develop an external oil leak from the head gasket at the back of the engine. Make sure to inspect that area when buying one of these cars. Once the head gasket fails and is replaced, the new one should be good for another 100k – 150k miles.

This issue mainly affects the inline-6 engines, because of their long cylinder heads. However, the 4-cylinder M111 engines are also affected, but to a smaller degree.

M111 & M271 engines – “Kompressor” lifespan

These engines are fitted with superchargers. The superchargers are reliable but have a finite lifespan. I estimate that they will need to be rebuilt after around 150,000 miles. The engine and other components under the bonnet will last a lot longer, so it’s very likely that the car will need to have the supercharger rebuilt or replaced at some point during its lifetime.

M271 engine – timing chain stretch

Generally, when a timing chain is used, the intention is for it to last the “lifetime” of the engine (very roughly 200k miles). Leaving it for this long in the M271 engine is very risky, in my opinion.

There have been cases of premature chain stretch in these engines. As the chain stretches, at some point it will reach the limit of what the chain tensioner can compensate for. The tensioner uses oil pressure to apply tension to the chain when the car is running. There is also a spring that applies some tensions when the engine is off and there is no oil pressure.

What happens is that when the chain is stretched too much, the spring alone cannot apply enough tension, and it becomes possible for the loose chain to jump some teeth on the timing gears. I believe this is why most of the M271 failures occur during engine start up. When the chain skips, major engine damage can occur if the valve timing goes out of sync far enough for the valves to hit the pistons.

For some reason, Mercedes-Benz decided to use a single row timing chain in the M271 engine while its predecessors, the M111 and the even older M102, had double row timing chains, which were very reliable.

The timing chain should be watched in the M271. If it starts showing any symptoms of stretch, it should be replaced. It’s difficult to estimate precisely how long the chain will last. There have been cases of chain failures at 80k miles, and there are cars that go far past 100k without any problems.

In my opinion, you should treat the chain as a 100k miles service item if you want to be really safe.

You have three options:

1. Avoid the M271 engine entirely.

2. Get one that already had the chain and chain tensioner replaced. The replacement chain should be good for another 100k miles.

3. Buy the car, and plan to get the timing chain replaced at some point. The timing sprockets may need replacing as well if they are worn.

A typical symptom of a stretched timing chain is a chain rattle that lasts a couple of seconds after a cold start. In severe cases, the engine may be difficult to start as well. Usually, the “Check Engine” light won’t come on. Click here to learn more about timing chains and how to check them.

M271 engine – capillary action (oil in wiring loom)

The M271 engine is equipped with Variable Valve Timing (VVT). Mercedes-Benz employed VVT in most petrol engines from that time. The VVT system is operated using two camshaft solenoids attached to the front of the engine.

The solenoids occasionally develop minor leaks, which would normally be completely harmless. However, in the M271 the electrical plugs that connect the solenoids are pointing down…

What happens is that oil, leaking out of the camshaft solenoids, can enter the wiring harness and embark on a great journey through the wiring to the oxygen sensor, mass airflow sensor (MAF) and finally the Electronic Control Unit (ECU).

A pretty ridiculous problem, don’t you think?

This is possible because of capillary action – the ability of a liquid (engine oil in this case) to flow through narrow spaces (wire strands) without the assistance of any external forces. If this sounds astonishing, think about how difficult it is to predict such behaviour. Don’t be too hard on Mercedes-Benz engineers.

If oil gets into the wiring harness, most of it will end up at the oxygen sensor, which usually fails first. If the oil isn’t stopped, it may reach the MAF, and lastly the ECU.

The solution is simple – fix any leaks from the camshaft solenoids, and fit short extension cables (pigtails) so that the capillary action is interrupted at the pigtail. With the pigtails fitted, the oil cannot travel further to the actual wiring loom, which is plugged into the pigtail.

If you’re going to buy a car with the M271, I advise you to check the plugs on the cam solenoids for any oil. They are on the front of the engine and easy to get to. If the oil has already contaminated the wiring loom, then it will need to be cleaned or replaced.

Once you buy the car, fitting the extensions is cheap insurance – much cheaper than replacing the oxygen sensor, MAF, or the ECU. Please note that many cars will have the extensions already fitted – there was a service campaign regarding this issue.

M272 engine – soft balance shaft gears

The 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. 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 this a very expensive repair.

Engines with serial numbers higher than 2729 . . 30 468993 have the updated gears and are free from this problem. 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 engine – 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 of 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.

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 failure

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.

Black Death (CDI engines)

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 Mercedes-Benz W203 C-Class cars made in 2004 and onwards have better corrosion protection. They also have most of the bugs worked out.

• All W203 engines are fitted with timing chains, which normally don’t have a specified replacement interval. The timing chains in the W203 are generally reliable, with some exceptions, but they will not last forever. Click here to learn more about timing chains and belts.

• The V6 M112 (C 240 & C 320) and V8 M113 (C 55 AMG) engines – Mercedes-Benz got both of them right. They are closely related to each other and both are reliable.

• Look out for timing chain stretch in the M271 engines and head gasket problems in the M111 engines. Out of the two, I’d choose weak head gaskets over weak timing chains. Pick your poison.

• Watch out for balance shaft gear issues in the M272 engines. The balance shaft horror story and the overly complex variable intake manifold mechanisms are the only real issues with these engines. Once fixed, it’s not a bad unit. Unfortunately, Mercedes-Benz improved the balance shaft gears only in 2008 – a year after production of W203 stopped. Be very careful not to buy one with worn gears – look for a car that had them already replaced, or better yet, avoid this engine entirely.

• The pre-facelift cars may have issues with corrosion and build quality, while post-facelift cars may have problems with the engines (timing chains in the M271 and balance shaft gears in the M272).  Again, pick your poison.

• 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 in the OM642 engines and injector seal leaks (“Black Death“), the things that could go wrong with the CDI engines are typical for most Common Rail diesel engines.

• The diesel engines in the Mercedes-Benz W203 may have a diesel particulate filter (DPF). The 4-cylinder diesel cars produced in 2004 and 2005 had them fitted as standard. Other than that, it was an optional extra. However, it may differ between countries. 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.

• The 30 CDI AMG is the first diesel-powered AMG sports car. I wrote that it is a sports car specifically because the first diesel-powered AMG vehicle is the AMG MB 100 D from 1989, which is… a van.

• 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, expect the service costs to be above average.