After driving the Mercedes W203 just after my reliable Toyota Corolla E140, something in me changed. The car had a similar dimension, only slightly bigger than the Corolla, and still, it managed to seat me in the back with still sparing some knee room. The doors closed with solidity to them, after all the Mercedes W203 C class scored 5 stars for adults occupants.
Coming to the year 2024, the car has been long discontinued and it has been 17 years since the last model was sold new. The good news is that you can get it for a dirt-cheap price. And for that amount of money, you get an awful lot of a car. Here in India, we got five variants, three petrol and two diesel vis a vis C180 AT, C200k AT, C200k MT, C220 CDI AT and C220 CDI MT.
The diesel was the most desired as it had a respectable 340 Nm peak torque production and returned a mixed fuel efficiency of 12 km/l. Some chaps even build a drift car around the petrol MT ones (I was approached by one such dude in the morning and so this post).
Now, let’s see what are the common problems found in the Mercedes W203 C class. May this article help those who are looking to buy one used.
ABS Warning
ABS and SRS are the two most common warning lights that I see on the Mercedes W203 when I go on for their inspection.
Now, on a car that is more than 15 years old, this can be expected. Let me give you a gist of what may be wrong and what can you expect from your pocket.
ABS wheel speed sensor
If the ABS warning light stays ON and does not appear to be affected by the brake pedal usage, then most likely the ABS wheel speed sensor has gone kaput.
These sensors are installed on two wheels (or on all four) diagonally. I have seen it is not the sensor that fails (not always), but the ABS magnetic ring seals that seat on the hubs. These get dirty with grease and crud. You may need to take it out and clean it. Just remember to seat it flush exactly it was before. I have seen that folks push it too deep into the hub.
But, yes, if that does not solve the issue, first get the car scanned at a competent independent garage that has a good scanner that scans all the systems. it should point out what sensor is faulty. Replace it with another wheel and see if the problem shifts to that sensor. If it does, then you are the culprit.
The ABS wheel speed sensor for the Mercedes W203 costs about 15k at the dealership and 3.5k from an aftermarket brand like Meyle.
Brake light switch
The brake light switch on Mercedes cars is used for triggering the brake lights when you push the brake pedal, but also to send a signal to the ABS. And so, this could be the reason why the ABS warning light comes ON when you press the brake pedal.
These can be repaired, but takes a bit of patience and expertise. Inside is a simple spring-loaded metal contact mechanism (on most cars). Most of the time, there would be a carbon deposit or the metal contacts not bent enough to make a contact (to complete the circuit) with each other as they move. You can fix it once you open it.
Not feeling confident enough? Then buy the brake light switch from Mercedes for about 3800 bucks. You can find this part with aftermarket brands like Meyle available at Boodmo for about 900 rupees. If you want to go even cheaper then look for this part at a scrapyard.
High-mount stop lamp
Not a common sight on a 15-year-old car, is it? People would keep driving without knowing that their brake lights do not work. I do not blame them, we do not have MOT like the brits!
So, the rear SAM (Signal Acquisition Module) on Mercedes Benz (which looks like a fuse box trunk) could determine that there is something wrong with the whole tail light even if one bulb is shot and may shoot the ABS warning light on the dash.
Also, check if the third brake light (the one in the centre) works. Feeling spirited? Check for the connections for corrosion and wires for breakage. Not common for these things to happen on an old car.
The fix is simple, repair the wiring if it is frayed. Clean the connections and lastly replace the bulbs.
Drained or incompatible battery
Often when the owner is getting rid of their car they sell it as is to the car dealer. And to maximize the profit, the car dealer would do the basic repairs and let the car become a headache for the next owner.
And this is the perfect example of installing a smaller capacity battery in the Mercedes W203. Most would get away with this but it becomes a nuisance to own. The car would crank slower and may throw a bunch of warning lights on the dash including the ABS warning.
So, check whether your car has a 100 AH battery installed. If yes, then check whether it has enough CCA (Cold Cranking Ampere).
AC stepper motor arm (clicking sound from the dash)
If you notice click click click (a timed clicking sound) when you turn the AC ON or if you are unable to turn ON or OFF the driver or passenger foot-well (depends if your car is LHD or RHD) airflow, then most likely the plastic arm that shifts the airflow is broken.
Mercedes revised the design two times, adding more plastic to the plastic arm to make it more rigid.
And it affected only the early models i.e. before 2005.
As many folks on the internet have suggested that it is the plastic arm that gets damaged and not the stepper motor itself, the fix does not require the motor, just the arm. But to get to that arm would require you to disassemble the whole center console.
The great thing about the car communities is that everybody likes to pitch in and so, we have a step-by-step guide by members of mbworld.org. You can download the guide’s PDF that they have made, too.
Or watch the video by NK1794 on Youtube. He has covered pretty much everything and it gives you an idea of whether you need a professional to undertake this task or not.
SRS warning light
You will need a good scanner that can scan the whole system on the car including the airbags. Because finding the exact fault is difficult on this issue as there are many triggers. So, buy a good scanner or rent or just take it to a good independent garage.
Let me take you through all known issues that can trigger the SRS warning light.
Also, it is not advisable to drive your car with this warning light ON as it may prevent the airbags from deploying in case of an unfortunate accident.
Seat-belt Buckle
The wires to the seat-belt buckle may have gotten loose or frayed. You can look underneath the driver and passenger seats for any traces. Many times if the vehicle was driven daily, the problem is most likely to occur thanks to the way Mercedes routes its wires.
You will need to replace the seat-belt buckle if there is no chime when you sit without the seat-belt ON. Or maybe there is some problem with the wiring itself, trace it down and look at the yellow connector to the CANBUS junction under the seat.
But even after performing the repair, you will need to clear the DTC.
Seat Occupancy Sensor
Another common failure on the W203. It can be diagnosed with a good scanner like iCarsoft i980 that can point out exactly the part that has malfunctioned.
The seat occupancy sensor replacement requires you to pull out the seat and remove its bottom cover (where your bum lands). There are youtube guides that will help you. I shall link one below.
Low battery voltage
Mercedes Benz cars are very sensitive to low battery voltage as they have a lot of electronics running around the car. If the voltage drops below a certain level, the car’s sensor may start sending incorrect data ultimately shooting a warning light on the dash.
You can check the battery voltage on your Mercedes W203 by accessing the secret menu. Follow these steps.
Turn the key to position two (right before the engine crank). The dashboard should light up like a Christmas tree.
Turn the key to position one and press the R button (or trip reset button) three times.
It should display the battery voltage. A healthy battery should be at 12.6V and a good battery would be showing 12V plus.
Other factors
These are unlikely but can happen. Some other factors causing the SRS warning light to pop up on the dash are –
- Faulty airbags
- Seat belt pre-tensioner
- A damaged connection to the impact sensor
- Steering wheel clock spring
Transmission problems
The five-speed Automatic
If you are not able to shift the gear selector lever from P to N and vice versa or the car is not shifting upwards of 1st gear, then the issue could be inside the gear selector housing.
People have discovered that some of the other circuital parts break their soldering point and that leads to failed transmission problems.
The easiest way to sort this thing out is to bake the circuit board in an oven at 200°C for 8 minutes. Seems like a foolish task but this process solders all the loose points on the circuit without even needing to identify one.
Just be very careful taking the circuit out of the oven as all the connections would be loose and the board would be hot. Post that, let it cool down and re-install. The problem should go away.
If it does not, then you may have to take it to a professional as you might have to check for electrical connections, software glitches and vacuum leaks.
Six-speed manual
Replacing the gear oil fixes the rough shifting issue on the six-speed manual transmission. So, make sure you do it first thing after getting the vehicle in your hands. Or make it part of the deal and let the previous owner bear the cost.
People living in colder regions may experience a hard shift from 1st to 2nd gear when cold. After the vehicle warms up, the problem goes away. Do check if your car has the correct gear oil level and the right grade of oil. And if that checks out, then just let the car warm up and drive then. Six-speed manuals are sensitive to cold and so they may weird noise when shifting from 1st to 2nd when cold.
Then some people have replaced the gear oil with the synthetic ATF and the notchy-ness just went away. Take a look here. And this method is not at all recommended. So, try replacing the STF gear oil with a new one. The 716 series gearbox uses 75 W80 API-GL4.
Diesel engine problems
The OM646 diesel engine is pretty solid. It did not give any trouble to its owner and this is well documented.
Just like all other diesel engines, regular maintenance can give the Mercedes engine long life. And many European countries have Mercedes cabs that have the same OM646 four-cylinder diesel engine. This is a testimony to their reliability and longevity.
Just clean the EGR, replace the fuel filter (at every 20k kilometres) and replace the injector seals if they leak. And that’s about it.
Other things would include the replacement of motor mounts, auxiliary belt pulleys and idlers when the time comes.