So when I lock or unlock the drivers door with the key fob or the on door buttons the driver door lock doesn't unlock or lock completely. If I do it manually on the inside or from the outside with the key, it works fine. Although it does take a little more effort manually than I think it should
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The passenger lock seems to work fine.

Do I just need to lube the mechanism inside the door or is something else wrong?

This is on my 1999 gmc Sierra 1500 rcsb 2wd

 

You can just some lithium grease spray on the latch and moving parts but it may do nothing.

The whole lock actuator may need replacement, it is only 18+ years old at this point.

 

Ok thank you, pull the door apart and take a look.

 

If I give the actuator (I'm guessing) a minute or 2 before trying to lock it or unlock since it was last used it seems to still work correctly.

Does that pretty much guarantee the actuator will need replacing?

 

Hows the battery voltage? (assuming this only happens when the truck is not running)

I have recently had a similar issue with my 2000. Lubing the lock mechanisms helped.

 

 

I have the same issue. sometimes my passenger handle won't go back in the bucket after opening the door and it will not allow the door to open

 

As others have stated, I've had success with cleaning the old grease off and re-lubricating everything - mechanism and actuator rods.