Fob won’t unlock, possible BCM issue?

[TomH91]

Started having some odd things happen with the key fob, door key and locks recently. They may not be related. Yet, I wonder if any of this points to a failing BCM. 2003 Suburban 2500 LT with power locks and a remote lock/unlock fob. Bought it in Nov 2023 and had no issues until Thanksgiving week 2024.

1. The key fob stopped unlocking the doors remotely. I replaced the fob battery, then tried a backup fob. No joy. Both fobs will lock the doors remotely, though.

2. At the same time, the door key stopped unlocking the driver door from the outside. For a while, it would unlock the door if I’d locked the doors from the interior door lock button as I got out, but it wouldn’t unlock the door if locked from the fob. Before long, the key stopped working the driver’s door lock at all. It still usually unlocks the passenger door. The backup key, less worn, is no better.

I figured these were separate issues until….

3. I took a call today as I pulled into a parking lot. I stayed in the truck. The doors are set to unlock automatically when Park is selected, and I re-locked the doors from the power lock button with the engine off. I chatted a while. When I ended the call, the doors wouldn’t unlock from the inside using the power lock button. It was like the door locks were disabled when the retained accessory power timed out. It shouldn’t do that, right?

 

[Fless]

Help me understand -- when you say that the door key stopped unlocking the driver door, do you mean that it wouldn't turn the cylinder? Or that the key would turn but the latch wouldn't unlock the door?

If it would turn the cylinder but wouldn't unlock the door, either the short linkage that goes from the cylinder to the door latch has come out of the plastic retainers, or the door latch itself is defective. I suspect the latter or a poor electrical connection. I think that the lock mechanism from the cylinder is mechanical, though. You may have more issues than that.

Probably looks something like this inside the door panel (the open - in the pic - yellow plastic latch on the right is the bottom link to the door handle; the round yellow one hidden behind it goes to the lock cylinder linkage, red plastic at the top):



From Rock Auto:

 

[TomH91]

Good question, thanks for asking and adding color. The key will not turn the lock cylinder on the driver’s door.

I figured these lock cylinder was bad, at first, until I noticed that it seemed to matter if the door was locked from the fob v. Locked by the power lock switch.