Electrical

Raymond81

I have a 2009 tahoe ltz. I just recently purchased this vehicle as used of course and the door locks work off and on. Some days all doors lock and unlock some days they don't. Sometimes just 2 doors unlock or lock. I was just curious if anyone has had the same problem. And also I had touched the negative post on the battery and it gave me 2nd degree burn. I'm wondering if that's part of my problem. Thank you.

imidazol97

Things to look for are whether the doors that don't lock or don't unlock are the same each time and is it the same whether you're using the remote to lock/unlock or one of the front door switches to invoke the lock/unlock cycle.

If it's consistent despite the mode of input to the body control module, I'd look for the communication line that goes from the driver's door to the other doors. I know about H-bodies sedans and the 2000-5 leSabre type cars used a tan wire or similar that went from the driver's door module (the master module) and communicated with the modules in each of the other doors to cause lock/unlock and window up/down. This tan wire went under the driver seat near the center and to a connector with the other 3 wires. This connector corroded with moisture or time. That affected the communication signal. Cleaning and refreshing that connection fixed many problems.

I do NOT know if the window controls in the Tahoe you have use the same system, but do the windows on the other doors work from the driver's door master module?

Raymond81

Thank you for your input. But yes all windows work. As for the door locks, it's still random whether you use the key buttons or the door switch. Most of the time it'll work the 1st time but then it won't after that. I'll have to wait a bit. On a side note.. When they stop working I'll try again and you can see the locks move but they won't pop up. Now that I remember they sometimes pop half way up then won't work again for a bit. Lol I've never seen this before. Either they work or they dont

imidazol97

If it seems random..., what do you feel in resistance when you pull the lock post up? Is there extra resistance? Did someone replace the posts with something ornamental that's different in size or something?

A possibility is that the motors that activate to push or pull the rod that goes to the door lock mechanism, the actual latch itself are getting weak.

Another possibility is there is friction in the door mechanism which is a bunch of odd shaped and engineered parts to be able to lock, unlock, latch and hold, and unlatch and release the part that holds the door shut. You might try squirting a light lube into that mechanism to hope some finds its way to free up a friction area.
That mechanism IIRC includes sensors to tell the computer that the door is closed and latched--I believe.

I have no idea the dust and dirt environment those lock mechanism have been in. So I'd start with a light lube that can spray into them. I have even tried spraying down from the door sill top to hit that mechanism...

If you're fairly handy, I'd look for videos on how to remove the door panel on your specific vehicle, and get inside to look at this. Be sure to use a weather proof glue to put back any watershield plastic that is there in the same way. On the H-bodies the tar like glue was shaped to direct any water that got into the outer door to drain holes to kept it from coming inside.

Good luck.