I’ve had my truck about 3 months and this weekend I noticed a problem.
My rear tailgate doesn’t lock. I use the keyless remote to lock the truck I can hear the doors latch close but when I try the tailgate it opens. I locked the truck using the controls on the drivers side door again I hear the doors latch but the tailgate still opens and the horn makes a small honking sound for about 30 seconds and then it starts honking very loud like an alarm. I locked the truck again using the remote I checked all the doors they were all locked, I checked the tailgate, and it opens. What’s up with that??

I’ve had my truck about 3 months and this weekend I noticed a problem.
My rear tailgate doesn’t lock. I use the keyless remote to lock the truck I can hear the doors latch close but when I try the tailgate it opens. I locked the truck using the controls on the drivers side door again I hear the doors latch but the tailgate still opens and the horn makes a small honking sound for about 30 seconds and then it starts honking very loud like an alarm. I locked the truck again using the remote I checked all the doors they were all locked, I checked the tailgate, and it opens. What’s up with that??

I believe there was some discussion about this a while back. If I recall correctly there is an adjustment that needs to be made back there. You might try doing a search with the Find button.

I'll give that a try. Thanx!

There was a bulletin issued on the door not closing all the way, but not sure if it said anything about not locking. If the door is completely closing, and fails to lock, sounds like the lock actuator might be bad (or disconnected).
Best thing is let the dealer look at it.

Here is the bulletin for the door not being aligned correctly.

Door Ajar Lamp On, Chimes Sound or Door Locks Cycle While Driving (Adjust Swing Gate Striker) #05-08-66-006 - (Oct 11, 2005)
Door Ajar Lamp On, Chimes Sound or Door Locks Cycle While Driving (Adjust Swing Gate Striker)
2006 HUMMER H3

Condition
Some customers may comment that the "Door Ajar" lamp comes on, chimes sound, or door locks cycle while driving.

Cause
The swing gate switch plunger may not be sufficiently depressed when the swing gate is closed due to door fit variation.

The information is very helpful. Thank you!