Blower motor will not turn off

Hi,

For some reason, I don't have a wiring schematic for this model. I have it for the CLK500, but not the 550. Regardless, I looked through the schematic for the 500. It isn't showing a relay for the blower motor. Take a look at pic 1. It shows the SAM module (signal acquisition module) with a relay internally. All systems on a Mercedes-Benz are controlled by the CAN Bus system and SAM units. The SAM functions as more or less a router for the computer system, and it can cause many different types of issues including things not turning off.

The first thing I recommend is to scan the CAN bus system of the vehicle for diagnostic trouble codes. Here is a video showing how that is done:

https://youtu.be/InIlnsjOVFA

The reason I would suggest the can scan first is simply I don't like removing power from the SAM module. It could cause other concerns. However, if you can't do that, try this.

Okay, what I want you to do first is remove the 40amp fuse (fuse 30) see pic 1 from the internal fuse box. Does the fan turn off? If it does, replace the fuse and remove fuse 51 from the SAM control module under the hood. Does the fan turn off? If it does, I suspect the SAM control module may be bad.

Note that in the pic, you see wires identified as CAN. That is where the different modules and computers connect together. This is why it is important to scan for issues using the aforementioned technique.

*****Also, please note that the schematic I used is for a CLK500 and not the CLK550. Check the fuses you remove to confirm they are correct.

Let me know what you find.

Joe