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15 Common Mercedes W204 Problems You Should Know

15 Common Mercedes W204 Problems You Should Know

What kind of problems does a Mercedes W204 usually have? In this blog, we’ve outlined the most important things you should watch for when you’re in the market for a Mercedes W204. However, let’s start with a quick answer:

The Mercedes W204 commonly has steering problems caused by power steering fluid leaks. Furthermore, rust and corrosion on the car’s exterior are also common. The headlights may fog, the car has several leaking problems such as oil and fuel leaks, and the BlueTEC diesel engines are known for causing stalling and loss of power. Finally, the transmission may start to slip, and the radiator can cause problems.

In the rest of the article, we’ll discuss every single problem in detail. Furthermore, we’ll tell you how to identify it, fix it and how much it costs to fix. Read on!

We Use Real World Vehicle Data To Create This List Of Problems

Before we dive into the most common problems, let’s quickly explain how we created this list.

This data comes from vehicle owners like you. It’s based on real data from real drivers. No guesswork or hypotheticals here.

We use resources like the National Highway Traffic Safety Administration, and many others, to review the most common complaints issues by owners along with the full history of recalls and active investigations.

From there, our team of automotive experts takes a closer look into each problem and breaks down why it happens, what you can do to prevent it, and how to fix it.

We review the data and interpret the results to make your life easier. Now that you understand how we came up with this list, let’s get into it!

Interior Problems

Steering Wheel Issues

The Mercedes W204, most Class-C, and even the SLK200 can come with several steering complications. The problems include the steering wheel locking with the ignition key still inside and the steering wheel making gurgling noises, especially while making a turn.

The most common causes of such a problem are the faulty power steering pump, also known as the vane pump, the fluid line for the pump, or a faulty internal seal. The power steering pump and the fluids help the driver steer the car effectively by maneuvering the steering wheel.

inner seal power steering pump mercedes w204
Location of leaking inner seal on power steering pump, Image courtesy

When the power steering pump gets damaged from somewhere, it can leak fluid and mess up the whole steering mechanism. Leaks from the pump or fluid line are easy to spot, but the inner seal of the power steering pump is more complex; therefore, we’ve included this location in the image above.

The cost to repair the leak is around $200-$350, but if the entire pump is to be replaced, it can cost about $400-$800, depending upon the severity of the damage.

Rusting And Corrosion

The Mercedes cars, including the C-class, are susceptible to rust and corrosion. It can appear at places such as the tailgate and the lower parts of the passenger doors. The company does provide corrosion and rust guarantees, but it has its terms and conditions, with the car having to have a complete dealership history and not being too old of a model.

Exterior Problems

Headlight Fogging

Headlights used in the Mercedes C-class and W204 have discharge gas bulbs as the source of light, and these bulbs are notorious for creating fogging or condensation inside the headlight compartment. The bulb can be replaced with a new one, but it does not promise a 100% guarantee of it not fogging up again.

Mercedes W204 headlight fog
Headlight fog on Mercedes W204, image courtesy

Wing Mirrors Are Making Squeaky Noises

Wing mirrors, also known as folding mirrors, can squeak or make noises, while folding is caused by the wheel installed in the mirror, which helps it fold inwards.

To fix this problem, the wheel inside the mirror can be replaced, which is cheap, or the whole folding system has to be replaced if the problem is to the extent of the mirrors not folding at all. The cost can be around $100-$300, depending on the specific situation.


Older models of Mercedes can often experience this problem as time and usage renders the oil gasket and the fuel tank almost useless and has to be installed with a new one.

Oil Leaks

The faulty ‘O’ Ring can cause oil leaks in your W204. You can determine this by checking for dark oil puddles under your car or a weird smell of burning oil.

Most Mercedes models, from the earliest W136 to the newest BlueTEC, have diesel engines. The problem with diesel engines is that they are more liable to oil leaks as the oil gasket of the engine wears and deteriorates over time, and hence you are more likely to experience such a problem, including other models like the Mercedes CLA.

The oil leak can be fixed by visiting your mechanic and letting him inspect the car. The ‘O’ ring can be replaced by a new one depending on your mechanic’s inspection analysis.

Fuel Leaks

The fuel leakage may occur in your car, and the prodromes include a strong fuel smell coming from your car, or the car is using more fuel than average. In some cases, it may appear that your fuel tank is holding less fuel but that’s typically a more severe leak.

The most common root cause of a fuel leak is the fuel filter being defective or damaged or not performing its job efficiently due to dirt and contaminants from the fuel getting stuck on the filter and causing a blockage. This blockade can then result in the fuel leaking. A fuel filter replacement can cost around $100-$200.

Getting the fuel filter changed or cleaned can easily fix this problem. If that is not the case, another cause for the leak can be the fuel tank being punctured. Get the fuel tank changed, and you are good to go. An aftermarket fuel tank (around $200) is the preferred choice as the OEM ones are super expensive.

Engine Problems

Since most of the Mercedes, including the E-class, GL-class, GLK-class, M-class, and models with the BlueTEC engines, run on diesel. And diesel engines are not that reliable over the long run compared to petrol engines, hence the recurring problems. The engine model for the W204 is OM646 which was introduced in 2008. Read here more about all issues a Bluetec engine can have.

However, you do avoid some of the other Mercedes problems like the louder engine that we see in the ML350.

Diminished Engine Power

If you feel a decrease or reduction in the engine’s power and you feel like it has a lower power output than usual, then there are several reasons why this may occur;

  • Faulty high-pressure fuel pump.
  • Clogged fuel filter.
  • Faulty Crank-shift sensor.
  • Low air compression.
  • Faulty spark plugs.
  • Faulty injector pumps.
  • MAF problems.

Besides these, one of the most common causes of reduced power is the damaged air hose which regulates the airflow and the compression and depressions crucial to the proper working of the engine. This can be fixed by replacing the air hose, which usually costs around $50, give or take.

In the case of this owner, it was a faulty high-pressure fuel pump

Engine Stalls

The engine stalling or not starting is a common problem for Mercedes earlier or older models. It can either be that the car stalls and stutters while driving or does not start and poses difficulty in restarting the engine.

The fault causes this in the Crankshaft Position Sensor, also known as CPS, which is the component of the engine responsible for powering up the engine and performing other ignition tasks. A fault in this sensor results in the engine stalling, and you cannot restart it.

Some of the most common symptoms of a faulty CPS to identify include the excessive vibrating of the engine, the car being unresponsive to acceleration, stuttering, stalling of the engine, etc. To fix it, visit your mechanic, who will inspect and replace the CPS, which usually costs between $17-$22 and is not that cost-effective.

Fuel Injector Is Damaged Or Broken

The fuel injector of a car is the electrical contraption that sprays fuel into the car’s piston cylinders through a tiny nozzle to ensure that the fuel sprays and distributes evenly. It can be a common problem in a wide range of vehicles from the massive Silverado 2500 to the cousin of the W204, the CLA, and of course the ML320 CDI as well.

This small component of the car’s engine is responsible for the smooth and efficient working of the car and its engine and ensures that the combustion process carries out smoothly. The degrading of this component can result in a fuel injecting problem, which messes up the fuel intake and performance of the car.

The earliest red flag for a faulty injector pump is choking the engine, especially when you step on the accelerator, and this can identify this. This problem is more common in diesel engines, this model being one of them.

This issue can be resolved by replacing the fuel injector. Fuel injectors are usually expensive and cost-effective. For this model, the injector parts can range between $700-$800, exclusive of the labor costs that can range between $300-$400.

Irregular Acceleration And Car Jerks Due to Faulty MAF (Mass Air Flow)

The MAF of the W204 is located right under the hood and mounted on the rear side of the engine assembly. If your engine hiccups, stalls, and has reduced acceleration, then the underlying cause can be the MAF filter being clogged, damaged, dirty, or hindered.

MAF sensors can detect how much and at what temperature the air flows into the engine assembly and determine the fuel injection rate carried out by the fuel injector according to the airflow ratio.

If your car has a mileage of over 50,000, then it’s high time to get your MAF sensor checked. Also, the check engine light will light up on your car’s dashboard, indicating something is wrong in that area.

You can check if the MAF is working correctly or not by simply letting your engine run while following the below steps carefully (also see the video below);

  1. Lift the hood and secure it in place.
  2. Remove the engine cover by pulling from the left and right edges.
  3. Locate the MAF sensor, which you will find at the rear end of the engine contraption placed after the air filter.
  4. For the wiring harness:
    1. If the wire harness for the MAF filter is accessible and in your reach, then unplug the wire harness (be very cautious with this step as the wires to the harness are very delicate and can also cause electrocution)
    2. If not, the air filter must be removed from its place, and it’s best recommended to get professional help.
  5. Once the wire harness is detached, if the MAF sensor works correctly, the car’s engine will stop running. If the MAF sensor is faulty, the car will keep on running.

It is handier to get an OBD scanner for such a diagnosis. Once the analysis has been done, the MAF sensor can either be cleaned using an industrial MAF cleaner or replaced by a new one that costs around $30. Never change or clean a MAF sensor with the engine on.

Transmission Problems

Clunking Noises While Shifting Gears

Clunking or sputtering noises while shifting gears?

It means your car is experiencing transmission issues with the gearbox mechanism. Your car’s transmission valve body is a complex system of circuitry, electrical components, and hydraulic elements that administer the transmission fluid to the right place.

Several things can be wrong with the transmission valve, resulting in knocking noises. Some of the common ones include

  • The air compression inside the valve is not being appropriately regulated.
  • The transmission fluid looks charred or discolored.
  • The transmission valve is damaged.

Your car’s mechanic can determine the underlying issue. The transmission valve body can either be fixed or reinstalled by a new one that costs between $450-$800, with parts and labor costing several hundred dollars.

Slipping Of Gears While Shifting

If you experience the following problems;

  • If your gear slips and slides while shifting.
  • It takes longer to shift gear from one to the other.
  • Revs higher even before you change gears.

Then you might be experiencing some transmission issues. Also, never ignore the “check engine light” on your onboard computer, as it can identify the engine and transmission performances and detect any problem the driver may have overlooked.

Gears slipping is hazardous and can endanger your safety and other people if not fixed, with several possible causes for this issue. Get your car serviced and checked ASAP to determine the principal reason that usually relates to either the transmission body being old and worn out with time or something wrong with the transmission fluid.

If you’re experiencing any problems with your transmission, performing an automatic transmission reset first is worth it. In the video below, there’s a good explanation of how to do this on the W204. Essentially, this allows the transmission to re-learn how to properly shift, fixing many problems for Mercedes owners.

Radiator Issues

Thermostat Valve Is Broken Or Is In Open Position

The temperature gauge on your car’s onboard dash indicates the temperature of the coolant in the radiator. The standard temperature for the car at rest position is 80-85 degrees. The W204’s temperature can increase up to 90-95 degrees while running, which is considered completely normal.

Now, if you notice that the thermostat reading shows abnormal temperatures both at a standstill and on the road, then there is something wrong with the thermostat. If the thermostat valve is either broken or punctured at points or what is usually called the “open position,” then the coolant will spill all over into the radiator without any regulation, and your car’s engine temperature decreases sufficiently.

Any temperature under 60 degrees is not okay for the car’s performance as the car will eat up more fuel and the mechanical parts are more liable to wear. A thermostat valve costs around $20, including labor; you are expected to pay about $100.

Coolant Appears Charred Or Black

If you notice that your radiator’s coolant appears charred or black, it indicates increased rust, dirt, and contaminants in the coolant. As the coolant for W204 is water-based, these contaminants hinder the radiator’s overall performance and cause overheating of the engine, which is not fixed early, can cause vandalization and damage to the engine components.

It is best to get the coolant flushed every five years or after a mileage of 100,000. Coolant replacing costs for the W204 vary with specifics, with labor costing between $150 to $200.

Failure of Water Pump Causing Engine to Lose Temperature

If the water pump in your car leaks or becomes faulty, it will constantly spill coolant into the radiator and excessively cool down the car engine, resulting in the car’s temperature gauge reading decreasing and deeming the engine inefficient. After leaking, the coolant will run out, and the engine will overheat and cause the ball bearings and the fluid gaskets to deform.

The installation and labor costs of the water pump for W204 are costly and heavy on the pocket as a new thermostat must be installed on top of the water pump replacement. On average, the water pump replacement can cost around $200-$300 for the aftermarket stuff. 

Closing Thoughts

While the Mercedes W204 is a well-engineered and aesthetically pleasing vehicle, it does come with a set of common issues that owners or potential buyers should be aware of. Power steering fluid leaks, rust and corrosion, foggy headlights, oil and fuel leaks, problems with the BlueTEC diesel engines, transmission issues, and radiator troubles are some of the significant concerns you might face.

Despite these challenges, it’s important to remember that many of these issues can be diagnosed early, mitigated, or even prevented with regular maintenance and vigilance. This not only keeps the vehicle in prime running condition but can also save you time and money in the long run.

You’re also going to run into problems in any vehicle, and certainly Mercedes. Whether we’re talking about transmission in the 4Matic or motor issues in the ML320 there are going to be problems.

However, understanding the nature of these issues, identifying their symptoms, knowing the fixes, and being aware of the cost implications are crucial steps in prolonging the life of your Mercedes W204. Being proactive about maintenance will always pay dividends in terms of vehicle performance and longevity.

This comprehensive examination of the W204’s common problems should serve as a valuable resource in your vehicle ownership journey. As with any luxury vehicle, the key is knowledge and proactive care. Here’s to many enjoyable and trouble-free miles in your Mercedes W204.

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