In our 2017 C300, when I try and sync the garage door openers to the buttons on the mirror, it will work but after a few hours, the buttons no longer work. Could it be that the auxiliary battery is failing, or could there be another reason?

Thanks,

Frank

What opener. If your opener has a roaming code (their term) things can get funky. We had a ton of issues with our old opener. The new one (Chamberlain) works perfectly in all of our cars from 2004 to 2024 and our RV.

OP, see if this helps: https://mbworld.org/forums/glc-class...door-code.html

Thanks. The Chamberlain opener that we have does not have a rolling code and syncs to our other car and stays that way just fine.

I see, the aux battery shouldn't hold the memory to homelink but it could, changing it might not be a bad idea. I think you know already but that battery is located underneath the passenger side footwell (if I recalled correctly).

Thanks for the suggestions. The opener took the Homelink sync code for the other car, after I tried to get the C300 to do so, so it would appear that the opener itself is still able to take new syncing codes. I don't think that it has been too long since the aux. battery was replaced.

No rolling code? How old is your GDO? Liftmaster and Chamberlain introduced rolling codes in the early 90s.

I don't think that the two separate Chamberlain units that we have the rolling codes. The Chevrolet synced, and held, with nothing else to do, after I tried the same with our MB which would not hold...

Not to argue, but it seems like the MB should be able to do what the Chevrolet did.

Hmmm I see.

Unless your GDO is 30 years or older, I'd be very surprised if it didn't use rolling codes. You can enter your vehicle and specific GDO model at the link below and get the exact steps to set it up. However, I just noticed that there's a gap in model years for the C Class. The 2015 through 2017 model years are suspiciously missing from the list. Not sure what that means, but you can try selecting 2018 and follow the steps.

https://www.homelink.com/program