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Mercedes-Benz C-Class: Why Don't My Power Windows Work?

Power windows could stop working for any one of a number of reasons, ranging from something as simple as an object stuck in the window sill to something a bit more complicated, like a mechanical failure in the window system. If you have a few minutes to spare and are interested in trying to diagnose the problem on your own, read through the following list of possible causes.

By Jeffrey Bausch - May 15, 2015

This article applies to the Mercedes-Benz C-Class (2007-2014).

A Mercedes-Benz C-Class is a high class vehicle, but at the end of the day it is still a car. As such, this means it is still prone to some of the headache-inducing complications and failures of even the more common cars on the road today. One example is when the power windows fail to work. This could be due to many reasons; fortunately, it’s easy to diagnose. Read on to learn how you can find the source of this problem in your C-Class.

Materials Needed

  • New power window relay
  • New power window motor
  • New power window regulator
  • New power window switch
  • Voltmeter (optional)
Figure 1. Functioning windows save you many headaches.

Step 1 – Check the power window relay

It might need to be replaced.

There are a whole bunch of reasons why the power window relay might be faulty, including a broken wire, the connection plates being clogged with debris, and more. While a broken wire can be easily soldered back, if the relay in your C-Class is old, then you will need to replace it in order to get everything working properly again. They typically run $25 and are easy to replace.

Figure 2. Window relay module.

Step 2 – Check the power window motor

A part of it could be broken, rendering the entire system useless.

The power windows have a motor that is responsible for moving the windows up and down. The regulator serves as the harness anchoring the car windows, and its gears get rotated by the motor. If any part of this system is old or otherwise damaged, everything will go caput. A good way to tell if this is the root of your problem is if one of the windows does not move up or down, but the others do.

Another way to diagnose this problem is if you test the window relay with a voltmeter—if it has power, the problem is in all likelihood the motor. A new power window motor for a C-Class is about $60.

Figure 3. Power window motor.

Step 3 – Check the power window regulator

This component is subject to a lot of friction and might be worn out.

We kind of touched upon this component in the section above, but it deserves a bit more exploring as it could also be a reason why your power window system isn’t functioning properly. This part is located on all the doors that hold the mirrors in place. When the motor is running after the power window switches are on, it rotates the window regulator gears to move the windows up or down. Unfortunately, the regulator is exposed to a lot of friction, which causes its gears and hinges to wear out. Typically, this results in the windows being stuck in the door frame. Other times, the window falls into the door frame and stays stuck there. If this happens, then the regulator needs to be replaced—they cost about $50 on eBay.

Figure 4. Window regulator.

Step 4 – Check the main power window switch

The main power window switch is more prone to damage caused by factors like spilled drinks and rain.

The main power window switch is tasked with controlling all functions of the windows. Unfortunately, being located on the driver’s side, it’s not in the best position, as this makes it prone to damage from spilled drinks and rain coming through the driver’s side window. When damage happens to the main power window switch, a replacement is necessary. You can buy a new one for about $65.

Figure 5. Window switches.

To learn more about how to determine why the power windows in your C-Class are not working properly, check out these related discussions.

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