Ok, so this has me stumped. I have successfully synced my GLS homelink in the mirror to work with my Liftmaster garage door, and it will work for multiple days. Then it randomly stops working and I have to reset it all back up again. Is this is a multiple profile situation when my wife gets in and changes to her profile and I change back to mine? It hasn't been consistent in length of time either. First time it worked for 6 days before not working and this last time only 3.

Any tips and tricks would be greatly appreciated. I have only followed the instructions in the manual.

I don't believe Homelink is tied into the profiles.

This sounds similar to issues that affect all the automotive built-in garage door openers. The garage doors occasionally replace the cryptographic keys for security so when you link your car’s opener I’m pretty sure you need to click a button on the garage door motor unit (~learning button) so that when it replaces the key it knows to send the new key to the car’s opener for subsequent use.

AFAIK, all rolling code openers change the code with every use, so that wouldn't explain why it would work for several days and then not.

Even if it were to change the code each time, the car based opener will likely store a whole bunch of rolling codes (cryptographic keys) and if it doesn’t eventually get an updated batch of codes from the garage control unit then eventually the set it has will no longer be useful.

See https://en.m.wikipedia.org/wiki/Rolling_code

So. . . How does that explain that the rest of us never experience this problem? We have 2 MB's, addressing a single garage door opener, and over nearly 5 years we have yet to experience an instance of failure.

All I am saying is that for rolling code mechanisms there is often a step that you have to press a button on the garage unit within a limited duration of time or other similar step that people don’t do correctly (often because it’s poorly documented). This is a physical step that functions to authenticate the car unit and enable it to get future sets of rolling keys. If you don’t do this step your car unit may work for a little while as it uses the set of keys it recorded during the configuration step (sniffed from handheld garage remote) but will eventually stop working because the keys become stale and the garage unit didn’t know to send it new sets of keys.

With a quick pic of the Model# label on your Garage Door Opener - and you have the Yr/Model of your MB - on a weekday morning when "hold times" are shorter - place a call to HomeLink Customer Care (800) 355-3515.

HomeLink Customer Service is based here in the US - and they are very helpful and thorough in walking you thru to a solution.

You might consider before the call "erasing" the settings in your MB - with car on - press both "outside buttons" (#1 and #3) simultaneously - hold both for about 1min (which seems like a long/long time) under the indicator light changes color.

HomeLink is very helpful..

Thanks everyone for your help. I am going to reset the homelink in the car again and then do the extra step of pressing the learn button. A little surprised as I have had homelink in my previous cars (Honda's) and they have never made me press the learn button. Is this a better security feature in the MB if it is needing to store more codes than what you can "sniff" from the garage door opener method told to use in the manual? We have a nicer Liftmaster at our home.

To make it easier here are the directions from the PDF version of the 2020 GLS. The highlighted portions relate to the learn button on the garage motor unit that I was referencing.

My 2019 W213 (could be same Homelink module) would "forget" its garage door opener settings every month or so when the car was brand new. It was very irritating and yes I was programming it correctly. Then after a few months of ownership, I received an OTA (over the air) system update for the car, and it never forgot the setting again after that. No hardware changes at all, just something in the software.

When we brought my wife’s GLS home a couple months ago, I programmed our rolling code opener and it worked for two days then it would need to be reprogrammed.

after several days of chewing nails, it figured out I made a mistake. I pressed the programming button on the opener, then held the button in the car while holding the opener’s remote. And it worked. BUT... I forgot to press the car’s opener button a couple more times to open and close the door.

Once I actually completed the WHOLE procedure, it has worked perfectly for the last eight weeks.

Don’t know if that’s your issue