I went to unlock the Hummer one morning with the FOB and it did but then the horn started beeping, the heat/AC ***** were flashing, and the fob wouldn't stop it. I had to actually start the truck to get it to stop! After that, neither fob worked, even after changing both batteries. Another thing, the heat no longer worked. That was actually an easy fix. Turned out the blend door actuator for heat was dead and after replacing it myself for $30 the heat works fine now. There was a video for that and I'm wondering if it was related to all the action that happened when my fob made things go wild. I've done extensive reading of posts and watching of YouTube videos and tried everything they suggested but still no key fob is working. I can't enter the programming mode to reprogram them myself. I took out the BCM, inspected it (looked perfect) and tightened the grip on the fob antenna connection. I'm at a loss. The doors work manually with the switch on the driver's door so I can lock the vehicle and then open it back up with the key and unlock them all using the switch. The fuses all look good. Logic tells me it comes down to reprogramming the key fobs since everything else is working. Odd that the one I keep in the house stopped working too though. I'm at a loss for what else to try. It might mean a trip to the GM dealer but I'm still not 100% convinced that will cure it. Does anyone else have any experience with this problem?

 

Sounds like you have a general electrical problem, and a separate remote keyless entry problem.

I'd start out by making sure your start battery is in good condition and if you still have the oem battery terminals, replace them with something more durable. Lot's of posts here about that.

Then, for the key fobs, look here for a recent post of things to try - lot's of steps to run through in that thread. On my truck I found corrosion in the wire harness connector that's just below the BCM behind the kick panel in the passenger foot well. Spraying both halves of the connector with CRC cleaner and letting it dry, then working the connector multiple times has resolved my issue (at least for now).

Whenever working connections around the BCM remember that some of those pins are always live, so disconnect the battery before spraying contact cleaner in there!

 

Please look at my post (#3 in the thread linked by NMH3). An aftermarket remote start will solve the need for fobs, provide 5-10Xs the range, and add remote start rather than pissing away time and money on resurrecting the dead fobs.

Example of how ugly it can get chasing antiquated OEM fob use... BCM Nightmare