Tech 2/ AC question

[02suburbanZ71]

Also thought of something while on way to doctors office just now. Does your truck have the auto lock feature? Can you change the behaviour of it? On mine I can set it to lock when put in gear, or lock at a low speed, and unlock when put in park, or when engine is shut off, and some others I think.

 

You may have a bad ground connection somewhere in that system. If the BCM thinks the truck is being put in park, it will unlock the doors. If the truck is not being put into park, but the BCM thought it was, as soon as the doors are unlocked, the BCM sees that you are doing 50mph and the doors are not locked, so it locks them. Take a look at how your truck is setup for auto locking, and maybe change that setting to see if the unlock/lock at 40mph still happens. If it does not happen anymore, then the issue will be in the circuit that was being used in the previous setting. For example, if you had it set to unlock the doors when put into park, and how it is set to unlock when engine is shut-off, there is likely a problem in the circuit that tells the BCM that the trans is being shifted to park.

Yes it has the auto lock feature. I'll drive it around see what happens then inspect it. Thanks for the help!