2011 GMC Sierra no cruise with A/C on

[Wells73]

Is there anyone who could point me in the right direction on what steps to take first? A/C works fine. Cruise control works fine if A/C is off. If A/C is already on, cruise power lights up but it never engages and displays on dash. If cruise is already on and engaged, it turns off as soon as I turn the A/C on. Any advice on things I can start checking? Thanks in advance. 

[Jsdirt]

I believe those 2 systems get power from 2 different points (not the same fuse). If that's the case, grounds are the issue. Problem is, the BCM supplies the ground to both.

 

What I would do is check all the basics. Start with the battery terminals, cables, and their ends. Then look over fuses and wiring. Look under the hood, around the underhood fuse box, interior fuse box, and underneath vehicle for any rubbed / chaffed / broken or corroded wiring, but start with the steering column area. If you run out of options, check the BCM power and ground - use a halogen headlight to make sure both the power and ground can handle the load. I've seen these show 12v and good ground, but wasn't even able to carry the current of an old 194 marker bulb.

[Wells73]

Side note - I just disconnected battery for 30 minutes hoping it would reset something.  Connected and started vehicle.  After 1 minute of running the negative battery terminal is hot enough to cook on.  Major resistance somewhere? 

[Jsdirt]

Yeah, heat = resistance. The more heat, the higher / worse the resistance is. Could try polishing up the ends of the cable with sandpaper or wire brush, or small wire wheel in a Dremel on low speed. If the heat is in the center of the cable, away from the ends, then a new cable is in order.

[Wells73]

Thanks Jsdirt.  I had an aftermarket repair negative terminal that looked rusty.  I replaced it this morning and ran the truck for 10 minutes and it never got hot.  Cruise control actually worked too.  Thank you for the quick reply!  I'll keep a close eye on it.  

[Jsdirt]

You're welcome - glad it worked out!