If your tire pressure monitor system is not reading. The problem is most likely the battery in the wheel sensor.
These sensors are Non-Serviceable according to BMW.
It is possible to replace these if you are willing to go there.
Get you 2 CR2032 batteries. One for each sensor.
(https://lawnmowwer.smugmug.com/Motorcycles/R1200GS/i-5BKM4Vb/0/M/smugshot_5001412-M.jpg)
So first take the wheels off. Then you must dismount the tires. I'm not going in depth here. If you aren't going to change a tire then you probably shouldn't try this.
Next cut the epoxy off the top of the batter. A razor blade worked well.
(https://lawnmowwer.smugmug.com/Motorcycles/R1200GS/i-v8MGGw5/0/M/image-M.jpg)
The battery is spot welded to the 2 tabs. You must break the welds carefully. Don't worry about the battery. Just make sure you don't break the tabs. I used a small screw driver and a pocket knife.
Should look like this when your done.
(https://lawnmowwer.smugmug.com/Motorcycles/R1200GS/i-mzqpd64/0/M/image-M.jpg)
Then I bent the bottom (negative tab) so that is was a little springy to hold tension against the battery. I wasn't brave enough to try to solder in a place I couldn't see.
I did however solder the top tab down.
(https://lawnmowwer.smugmug.com/Motorcycles/R1200GS/i-2fvDx6M/0/M/image-M.jpg)
Next epoxy back over the batter to keep moisture out and I hope it works.
(https://lawnmowwer.smugmug.com/Motorcycles/R1200GS/i-fLJQng4/0/M/image-M.jpg)
It is raining. So I haven't been for a ride. You cant tell if it works until you ride it. As the force of the wheel turning makes the sensor activate.
If it does work. I saved $285.
Was there a specific epoxy that you used or would any work?
I used a 5 min plastic repair epoxy.
Mainly because I forgot to grab some on the way to a friends shop to use his tire changer. That is what he had in hand.
Ok so it took 2 rides before they registered but are working fine now.
(https://lawnmowwer.smugmug.com/Motorcycles/R1200GS/i-gX2ZBDD/0/M/image-M.jpg)
Another option is taking your air pressure modules to Batteries Plus. The one in Huntsville on the Parkway went over and beyond to replace my batteries. Great service and good people. 8)