4WD issue. 99 Yukon.

[Charlie Vortec]

Lights flash when the truck starts but don't work after. It's stuck in 4WD high. New actuator, I had the TCCM out and back in. Today, the truck went into 4Wd low on its own while going through a parking lot. The lights stopped working. On the way home it shifted to high, but I can't change y. Any ideas?

 

[Sean Buick 76]

For now to get it back in 2wd:

Remove the negative battery terminal for 2 minutes then replace, start it up and then shift it to 2wd right away then shut the truck off and remove the fuse for the 4x4 system.

At least then you can drive it in 2wd.

Once you are ready to troubleshoot start with the ground at the t case, re do that. It sounds like a computer issue but who knows maybe it’s the switch on the dash. Have you looked T the t case encoder motor? There is a sensor inside that often fails

 

[Charlie Vortec]

For now to get it back in 2wd:

Remove the negative battery terminal for 2 minutes then replace, start it up and then shift it to 2wd right away then shut the truck off and remove the fuse for the 4x4 system.

At least then you can drive it in 2wd.

Once you are ready to troubleshoot start with the ground at the t case, re do that. It sounds like a computer issue but who knows maybe it’s the switch on the dash. Have you looked T the t case encoder motor? There is a sensor inside that often fails

Thank you. I'll try that in the morning.