Front axel shift selenoid.

[Geoffrey Moorhead]

2005 gmc Sierra 4x4 selenoid is stuck extended. Pulled it from truck and still won't retract. Is this thermal or elec?

[Jsdirt]

No such thing as a thermal solenoid that I know of in the automotive world. They're all electric. I'm not familiar with how they're designed internally - I figure it's probably an electromagnetic setup, with a chunk of metal on the end of the cable that gets yanked by the magnetic field.

 

Sounds like you need a new one. Those trucks were still built fairly well. Can't complain about 16 years of service in this part of the country these days.