15 Common Problems of the Mercedes W204 to Look Out For

15 Common Problems of the Mercedes W204 to Look Out For

Cars from the “Silver Arrow” brand are among the most revered examples of German luxury automobiles, and this includes even those that have been roaming around for over a decade, such as the Mercedes W204 C-Class.

But as with a certain close competitor with a two-colored Bavarian flag as its signature mark, the W204 wishes that it didn’t have any blemishes to fade its shine. But alas, it does have several of them.

So before you settle for a shiny yet not-so-new Merc of your own, let’s give you a rundown of all the common problems the W204 is notorious for and how to deal with them below!  

What are the most common problems of a Mercedes W204?

Common Mercedes W204 problems include reduced engine power, stalling, a faulty MAF sensor, a bad fuel injector, transmission issues, and radiator problems.

Other Mercedes W204 problems are oil/fuel leaks, foggy headlights, squeaky side mirrors, steering wheel issues, and interior rust/corrosion.

The Mercedes W204 is quite a popular option for many people looking to get a C-Class Merc, which despite what its name says, is actually classified as an executive “D-segment” car.

But like any other Merc, including its close relative the Mercedes CLA, you would struggle to find any secondhand sample that doesn’t have some sort of issue with it.

If you were to ask any C-Class W204 owner who has owned the luxury car for a couple of years, you’d find out that it’s a mix of both major and minor problems from the engine to the side mirrors.

Owners, reviewers, mechanics, and even Mercedes itself have been aware of the Mercedes W204’s flaws, and we’ve gathered every single one of those flaws here along with their possible remedies and even recalls for any future owner’s sake.

Engine Problems

Engine Problems

Some engine-related Mercedes W204 problems such as an overall reduction in power output, stuttering and stalling, a faulty fuel injector being unable to provide enough fuel, and a bad MAF sensor resulting in jerky acceleration.

1. Reduced Power

One of the most general problems that you can have with the Mercedes W204’s engine is that it may lose some of its power, making its throttle response and acceleration feel more sluggish than usual.

Now, the tricky part about an engine that has reduced power output is that there can be many reasons for this, and the W204’s OM646 4-cylinder diesel power plant is no different.

However, among all of the potential culprits, the one that most commonly robs power from the Mercedes W204’s engine is a damaged or cracked air hose. The improper airflow as a result of this would disrupt the delicate air-fuel mixture inside the engine.

Aside from a broken air hose, the engine can also lose power due to any malfunctioning component of the fuel system and ignition system, such as bad spark plugs and a faulty fuel pump. 

Mercedes W204 Reduced Engine Power Causes:

Damaged or cracked air hoseBad high-pressure fuel pump (HPFP)Bad injector pumpsBad/fouled spark plugs Dirty or clogged fuel filterLow air compressionFaulty MAF sensorFaulty crankshaft sensor

2. Stalling Issues (Bad Crankshaft Position Sensor)

2. Stalling Issues (Bad Crankshaft Position Sensor)

Aside from a decrease in engine power, you may also experience some stalling issues while driving or even just letting the engine run on the Mercedes W204.

Engine stalling issues are quite commonly reported for the W204 model, and it may initially start with the engine struggling to keep running before it eventually dies out.

Owners also commonly report that after the engine has stalled, it becomes difficult to start it back up again, making it a problem that can easily get you stranded anywhere.

Luckily, the culprit has already been found to be a fault in the crankshaft position sensor (CPS), an important part of the ignition system that is crucial in feeding crankshaft info to the engine management to keep the engine running.

While the most commonly associated problem of a faulty CPS is engine stalling, it can also be accompanied by other symptoms such as engine stuttering, an increase in engine vibrations, and unresponsive or delayed acceleration performance.

Simply replacing the Mercedes W204’s crankshaft position sensor or “CPS” for about $20 on average will resolve the stalling issues and the other possible symptoms mentioned above.

3. Faulty MAF Sensor (Jerky Acceleration)

3. Faulty MAF Sensor (Jerky Acceleration)

Another sensor that’s known to become faulty on the Mercedes W204 is the MAF sensor, and once it does, it can cause your car to jerk back and forth while accelerating.

The MAF sensor (mass airflow sensor) is tasked to do exactly what its name suggests, which is to detect and monitor the amount of airflow as well as the temperature of the air going into the engine.

The car’s computer relies on the MAF sensor to accurately calculate how much fuel should be injected based on the detected airflow, so if the sensor goes bad and starts sending incorrect readings, the delicate air-fuel ratio of the engine gets affected.

As a result of this incorrect ratio, your engine may feel like it’s struggling to accelerate properly, hence the jerky feeling whenever you push the throttle pedal. In addition, the check engine light (CEL) can also illuminate once it detects this happening.

In the case of the Mercedes W204, units that have already clocked over 50,000 miles are more likely to experience jerky acceleration due to a bad MAF sensor. Be sure to keep this in mind when looking at higher-mileage samples.

While it’s recommended to have it directly looked into by a mechanic, you can also diagnose the condition of a MAF sensor by following the procedure below.

How to Diagnose the Mercedes W204 MAF Sensor:

Open the hood by pulling the red hood latch located underneath the bottom left of the driver’s side dashboard.
Pull and detach the left and right corners of the engine cover to gain access to the MAF sensor at the back of the engine.
Carefully unplug the MAF sensor’s wiring harness from the rear of the engine. Depending on the W204 model, you may need to first remove the air filter to reach the wiring harness.
After disconnecting the wiring harness, check if the engine stops running. If it remains running otherwise, then you have a faulty MAF sensor.

A full-on diagnosis of the MAF sensor would require you to use a scanner tool such as an OBDII reader, as it will show specific fault codes that tell you the nature of the issue with the sensor.

Depending on the severity of the problem, you may need to either clean the MAF sensor if it’s too dirty or has been contaminated or replace it completely for around $40 to over $100 depending on the shop and your particular W204 model.

4. Bad Fuel Injector

4. Bad Fuel Injector

The Mercedes W204’s fuel injector is also known to become a problem area for the German luxury car, leading to all kinds of issues with the engine’s performance.

Fuel injectors are designed to provide calculated amounts of fuel for the engine combustion process, so if even one were to become faulty and start spraying too much or too little fuel, it would mess up the correct air-fuel ratio and cause the engine to run rough.

Hence, if you have a bad fuel injector on your car, then be on the lookout for symptoms such as the engine misfiring, a rougher engine idle, decreased acceleration performance, a drop in fuel economy, and the check engine light (CEL) turning on.

Issues with the fuel injector have been reported to occur more commonly in Mercedes W204 diesel models, which already had a service measure for their Delphi fuel injectors equipped on either early C220 CDI or C250 CDI Blue Efficiency models.

For other models not part of the service measure or so-called “recall”, expect to spend a total of about $1,000 to $1,200 for parts and labor when getting the Mercedes W204’s injectors replaced.

Transmission System Problems

Transmission System Problems

The two main problems that affect the Mercedes W204’s transmission are gear slippage and the presence of clunking and knocking noises in between gear shifts.

5. Gear Slippage During Shifts

Whenever the Mercedes W204 starts to exhibit issues with its transmission system, then one of the most common ones is that the gears feel like they’re slipping in between shifts.

When transmission gears slip, it means that the transmission is not engaging gears smoothly or is taking a longer time to shift between gears.

Gear slippage is made more obvious whenever you hear the engine revving high before dropping into the next gear, which results in a pretty rough transmission shift.

Furthermore, you will most likely get a check engine light (CEL) if you have transmission issues, as the W204’s ECU handles both engine and transmission parameters.

Some common reasons why your Mercedes W204’s transmission is slipping include a worn-out transmission body, dirty transmission fluid, or the transmission control module (TCM) needing a reset.

To reset the TCM on a Mercedes W204, which can apply to both the 5G-Tronic and 7G-Tronic automatic transmissions, we recommend following the reset procedure in the tutorial video below.

6. Clunking/Knocking Noises (Valve Body Issues)

6. ClunkingKnocking Noises (Valve Body Issues)

If you’re having transmission problems on a Mercedes W204, then expect it to make some sort of clunking or knocking noise from underneath, especially when shifting gears or slowing down.

Such unwanted transmission noises are usually traced to an issue with the transmission valve body itself, which is an entire mechanism within the transmission that redirects and distributes fluid to certain areas depending on the driving conditions.

Any problems with the valve body, such as physical damage, dirty transmission fluid, or an incorrect amount of pressure within the system, can make it hard to distribute the fluid to where it needs to be, resulting in knocking noises and shifting issues.

Costs to repair or replace the transmission valve body on a Mercedes W204 can vary between $450 to $800 depending on your specific transmission.

Radiator Problems

Radiator Problems

The Mercedes W204’s radiator is known to develop problems such as the water pump failing and the thermostat valve becoming faulty or getting stuck open.

The W204’s radiator coolant can get contaminated with dirt, rust, or any sort of debris, giving it a dark appearance that affects its performance.

7. Water Pump Failure

7. Water Pump Failure

A water pump failure on the Mercedes W204 could spell bad news for its radiator, as the faulty water pump can start to leak coolant onto it and cause a sudden drop in the engine’s temperature.

While it may initially sound like a good thing to have a cooler-running engine, it’s actually the opposite since the temperature sensor will mistake the engine for not running at the right operating temperatures, thereby reducing its efficiency.

But on top of that, the presence of a coolant leak alone is already a reason for concern since once it gets too low or runs out, you’ll have a high risk of overheating your engine and damaging its internals. 

The solution for this problem is pretty straightforward, which is to replace the faulty water pump with a new one bearing the same part number for your Mercedes W204 model.

However, you’ll also need to put in a new thermostat along with the water pump to ensure that they both function properly. 

It’ll cost about $100 to $500 for the water pump replacement, $100 to $180 for the thermostat replacement, and $25 to $45 to drain and flush the cooling system with new fluid.

8. Faulty Thermostat Valve

8. Faulty Thermostat Valve

A faulty thermostat valve is yet another component that can affect your radiator’s performance as well as the overall running temperature of your Mercedes W204.

It is the thermostat valve’s job to circulate the appropriate amount of coolant for the engine by either opening or closing at specific intervals.

If the thermostat valve gets damaged in such a way that it starts leaking coolant, then that can leak into the radiator and cause an excess amount of cooling for the engine temperature.

The Mercedes W204’s engine temperature is about 80 to 85°C when fully warmed up, then climbs to a normal operating temperature of 90 to 95°C while driving. 

However, a broken thermostat valve that’s leaking coolant can easily drop the engine temperature to below 70 or even 60°C, which will take a toll on both the engine’s performance and fuel efficiency.

It can be even worse than that if the faulty thermostat valve gets stuck in the open position, which means a constant flow of coolant will be fed into the radiator, causing an even sharper drop in engine temperature.

Thus, if you notice that your engine temperature is a lot lower even after running the car for a while, then make sure to take a look at your thermostat valve or simply “thermostat”, which costs about $100 to $150 in parts and labor to replace.

9. Contaminated Coolant

While it’s generally recommended to check your car’s coolant every now and then, it’s even more necessary to do so for the Mercedes W204 and its tendency to get contaminated coolant.

When the coolant gets contaminated, it can mean that a lot of debris such as dirt or rust has mixed in with the fluid, causing it to have a more black or “charred” appearance.

Genuine Mercedes-Benz coolant or “antifreeze” should be a clear, bright-colored, and water-based fluid. 

It costs about $25 to $45 for a Mercedes W204 coolant flush and replacement, which is recommended to be performed every 100,000 miles or 5 years, whichever comes first.

Exterior Problems

Some problems relating to the Mercedes W204’s exterior include various oil and fuel leaks, fogging of the headlights due to a bad bulb design, squeaky side mirrors/wing mirrors, and a rust-prone subframe.

10. Oil and Fuel Leaks

10. Oil and Fuel Leaks

Moving over to problems related to the exterior of the car, the Mercedes W204 is known to leak either oil or fuel underneath, making this quite a hazardous issue to have if not spotted right away.

Oil leaks on the Mercedes W204 have been observed to occur more frequently on the diesel variants, as their oil gaskets are fitted with O-rings that are more prone to wear out quickly and leak oil.

If you ever spot any puddles of dark oil underneath your W204 as well as smell anything burning, be sure to have your oil gasket and o-ring checked as they may already need replacing.

As far as fuel leaks are concerned, the most likely culprit is a faulty or clogged fuel filter. Apart from the leak itself, you’ll also notice that your fuel economy gets worse and the smell of fuel is more evident even from inside the car.

In other cases, there’s a chance that the fuel tank itself has been damaged or punctured and is leaking fuel.

If the fuel filter has gone beyond repair and cleaning, then it’ll cost about $100 to $190 to replace. Replacing a whole fuel tank, on the other hand, can cost $300 to $600 in parts alone if you opt for an OEM one and $200 for an aftermarket one.

11. Foggy Headlights

11. Foggy Headlights

Headlights are one of the most vulnerable components of any car, and the pair fitted on the Mercedes W204 happens to be prone to fogging and condensation.

But aside from being exposed to the elements, the gas discharge design of the W204’s xenon headlight bulbs itself is prone to develop moisture.

The xenon bulbs’ multi-connector also tends to corrode whenever it happens, so you’ll have to replace the connector together with the bulb. 

However, there’s still a chance that you may run into the same condensation problem again if you opt for the same OEM parts.

12. Squeaky Side Mirrors

12. Squeaky Side Mirrors

A more minor yet annoying exterior problem of the Mercedes W204 is that the side mirrors (also called wing mirrors) can start to make squeaking noises as the car ages.

The squeaking itself is caused by the wheel mechanism inside the power side mirrors, and you’re more likely to hear it whenever you’re folding them inwards or outwards.

One way of fixing the squeaking issue is by disassembling the mirror with a flathead and hex screwdriver, spraying some lubricant inside the housing, and cleaning any dust or debris buildup you can see.

If the squeaking still doesn’t go away after, then you’ll have to replace the entire folding mechanism of the side mirror that’s squeaking, which can cost $300 or more in parts alone.

13. Rusting on Rear Subframe

13. Rusting on Rear Subframe

Mercedes W204 owners don’t usually complain about rust on their luxury car, but when they do, it’s typically around the rear subframe.

Rear subframe rust has been plaguing the W204 generation of the C-Class, with some instances of the subframe completely failing and breaking apart due to how bad the rust is.

Owners that live in snowy areas that are subject to salt treatment have been the most prone to developing rusty and corroded subframes on their W204.

The good news is that Mercedes has extended the warranty of the rear subframe to up to 20 years and an unlimited number of miles. However, this is assuming that the rusting has already perforated or created holes in the subframe. 

Interior Problems

The most common problems with the Mercedes W204’s interior include different issues with the steering wheel and rusting/corrosion buildup on the doors.

14. Steering Wheel Problems (Bad Power Steering Pump)

14. Steering Wheel Problems (Bad Power Steering Pump)

One of the first things to look out for when it comes to interior issues in the Mercedes W204 is the steering wheel, as owners have had no shortage of problems with it.

From annoying noises while steering to the steering wheel locking up even with the key already inserted in the ignition, the reason for such issues has been traced to a problem with the power steering pump.

More specifically, the power steering pump’s fluid line as well as its internal seal can both become worn out, which causes the pump to malfunction and leak, resulting in the complaints mentioned above.

Depending on the nature of the damage or leak, you may be able to repair it for about $200 to $350. 

However, if the power steering pump completely fails as a result of the damage or leak, then you’ll have to shell out $400 to over $1,000 depending on whether you can fix it yourself or have a professional mechanic do it for you.

As part of the replacement process for the pump, you’ll also need to bleed the system and pour new power steering fluid in the reservoir, as most of it will come out of the lines once the old pump is removed anyway.

15. Interior Rusting and Corrosion Buildup

Apart from the rear subframe rust that we discussed earlier, the Mercedes W204 really isn’t known for having rusting and corrosion, but when it does, the first place to check would be the interior door panels.

More specifically, spots of rust and corrosion are known to form at the bottom of the passenger-side doors, especially for older model years of the C-Class W204 generation.

While Mercedes-Benz does have a warranty for rusting and corrosion, it is only offered for model years up to a certain age under specific terms and conditions by the dealership.

Frequently Asked Questions (FAQs)

Is the Mercedes W204 reliable?

The Mercedes W204 is generally considered to be a reliable car especially when compared to the older C-Class W203 generation, which had a lot more mechanical problems.

However, these cars are already starting to show their age, so you’ll have to make sure that you get a well-maintained sample of it when eyeing a secondhand model. 

Diesel models, in particular, tend to have the most issues when it comes to reduced engine performance and oil and fuel leaks.

What are the common faults of a Mercedes C Class?

The most common faults of a Mercedes C-Class can include acceleration issues, excessive vibrations while driving, transmission clunking noises, a bad MAF sensor, power-folding side mirror issues, and headlight bulb problems.

What is the most reliable W204 engine?

The most reliable engines offered for the Mercedes W204 models have been the 1.6-liter and 1.8-liter 4-cylinder “M271” gasoline/petrol engines due to having the least issues in over a decade and hundreds of thousands of miles worth of driving.

The 3-liter and 3.5-liter V6 options are also notable for their reliability, while the 6.2-liter “M156” V8 on the C63 AMG is also regarded as reliable for a powerful performance engine.