Battery back up puzzled

[waco]

Hello all, I am more accustomed to 67 -72 forum, but here goes. I have a 2003 Tahoe that twice now has come up with right rear door ajar code on my dash readout.

The first time it set off the alarm in the middle of the night, I found no attempt at a break in & after chasing the wiring to the BCM, I found no reason for the alarm. After about 6 days while driving down the road, it just canceled itself out. That was about a year ago.

Now, night before last I parked for the night & when I went to lock it up it showed up again.

I disconected the battery at the ground terminal last night thinking it might clear out any stored information giving me basically a reboot. This morning to my surprise I lost nothing but door ajar code. That problem solved for now.

Now the real question, is there some sort of backup battery in this rig I don't know about? I lost no radio settings or anything else that I can tell so far.

Thanks for your input. Andy