Hello, First post, long time reader. I have used this forum to keep my 95 C36 which is now sold and my 99 C43 running for some time.

I have run into an issue with the C43 I am hoping to get some help with. My sunroof, windows and sideview mirrors have been intermittently working and not working for several months on my 99 C43. When they fail, none of the systems work and sometimes a restart will fix the problem. This works less and less as time goes on. The door unlocking mechanism by key and trunk unlock have also been spotty, they work usually but not consistently, not sure if this is related or not. In order to resolve these problems so far I have replaced the battery (previous battery was over 10 years old and showing slightly lower voltage than it should be) and inspected/cleaned fuses. Systems worked briefly after cleaning fuses but have resumed not working. From research on the forum, it appears the comfort control module may be to blame for this issue?

My questions are as follows-

1) Is the comfort control module a likely cause for this kind of behavior?
2) Is there a way I can diagnose/confirm this is the issue before just buying a $500+ part?
3) Is it correct that the comfort control module is behind the battery on my car? I can't see it but have not yet pulled the battery to confirm.
4) Is the weak door unlock and occasional trunk not opening related or unrelated to the windows/sunroof/mirrors not working?
5) Has anyone had anything similar with their cars?

Thanks so much for the help, any and all suggestions/comments are sincerely appreciated.

I’ve had the same issue with the right or left window and mirror not working every now and then but resetting the battery works every time
I haven’t found a permanent solution for it yet but I believe it’s the comfort control module

Does your new battery hold charge as it should? Have you checked for any power drainage issues?


Whats the history of the car look like? Any service on anything related tov this issue?

Interesting, my problem was also an occasional one until somewhat recently, kind of a weird quirk. When you say resetting the battery do you mean just disconnecting it or is there a different procedure? Thanks

New battery tests fine and shows proper voltage with the car off and on. Accordingly I have not checked for power drainage, is that something you would suggest as it relates to this issue? I have owned the car for 4 years and I have not had any service related to this issue during my ownership, unfortunately maintenance records from previous owners did not come with car. Everything worked fine the first couple years and then it happened every once in a while for the last year or so until the frequency has increased to pretty much constant over the last couple months. Thanks for your help.