2019 Express Tire Monitor System and Key Fob

[98Z]

I have an Express 3500 series that keeps throwing the message to service the tire monitor system message on the dash. But wait, there's more...

The first time this happened, I didn't think much of it, but then I got out of my van, walked away and clicked the key fob to lock the doors and set the alarm. When I went to get back in, the key fob did nothing. Of course, I assumed the battery was just dead, so I bought a new battery. Nope. And since I had left my actual key in the van, I was effectively locked out. Hello AAA.

Some time later during that trip, the tire monitor system figured itself out and the key fob worked again. No issues for a while. Then it all happened again, except the part about locking myself out (I carry the key now).

I took the van to the dealership and they told me to bring it back when it was in the middle of the issues so they could scan it and see if it would tell them anything. Well, when it happened again, I wasn't near a certified GM mechanic. By the time I got near one, it had stopped being a pain in the ass.

Well, today I was lucky and got it there. They said my right rear tire sensor was bad. So, $144.00 later, I'm back on the road and on my way home. 40 miles later, "Service Tire Monitor System" again... right rear tire monitor shows "--", left rear shows "81".

Someone tell me what the key fobs and the tire monitor system have to do with each other? And what the hell is going on here? These certified GM mechanics don't seem to have a clue and no one else I talk to seems to get it either.