Cruise control turns off when Rear window Defrost is turned on

fastscirocco · Nov 21, 2022

Patient is a 2014 GMC Yukon XL Denali.

The cruise control will "shut off" the icon in the cluster goes away and the cruise stops functioning if the rear window defrost is turned on.
If I turn the defrost off the cruise works again. I tried disconnecting a cable from the rear glass and testing and it still happens.

I am stumped on this one, no clue what to check.

Blackcar · Nov 21, 2022

Wondering did you happen to led bulbs anywhere in your vehicle. Also, when rear defrost on does window gride get warm.

fastscirocco · Nov 21, 2022

The only LED bulbs I have are back up lights.

Blackcar · Nov 21, 2022

Is that something new the bulbs in backup lights.

fastscirocco · Nov 21, 2022

Blackcar said:
Is that something new the bulbs in backup lights.

No the bulbs have been in there awhile. They aren't on unless I'm in reverse, and the cruise isn't active then either. I don't see how it could be an issue.

wjburken · Nov 21, 2022

It’s a long shot, but put your car in park and see if any of the brake lights come on when you turn your rear defrost on. You might have a bad ground, or a short somewhere that’s back feeding into your brake light circuit making the cruise think you are applying brakes. Might have some one follow you done the road and see what happens when you turn in the rear defrost.

Blackcar · Nov 21, 2022

I installed led taillights and cruise quit working when headlights where on. Since cruise doesn't work when rear defrost is turned on just wondered if rear defrost turned on if it is working when plugged in.I believe when rear defog is on also mirrors defrost might have to get wiring schematics to look at what is going on.
I know it can be frustrating good luck getting to bottom of glitch.

fastscirocco · Nov 21, 2022

wjburken said:
It’s a long shot, but put your car in park and see if any of the brake lights come on when you turn your rear defrost on. You might have a bad ground, or a short somewhere that’s back feeding into your brake light circuit making the cruise think you are applying brakes. Might have some one follow you done the road and see what happens when you turn in the rear defrost.

I tried, no lights were lit.

fastscirocco · Nov 21, 2022

Update with added info:

It appears to be a little intermittent, the cruise stayed on with rera def on BUT as soon as I hiit the rear wiper button the cruise shut off. During tis series of tests the Cruise would work if either the rear Def or rear wiper was on but not both.
Then ~ 10 minutes later it went from being intermittent to all the time, as soon I turned on the rerar defrost cruise shut off.

More info, I had the rear tailgate glass replaced because a rear def tab had broken off. I'm wondering if there could be a ground issue. I have no clue what the wiring is like back there and called the glass shop that did the repair.

I appreciate any input, thanks

Blackcar · Nov 21, 2022

fastscirocco said:
Update with added info:

It appears to be a little intermittent, the cruise stayed on with rera def on BUT as soon as I hiit the rear wiper button the cruise shut off. During tis series of tests the Cruise would work if either the rear Def or rear wiper was on but not both.
Then ~ 10 minutes later it went from being intermittent to all the time, as soon I turned on the rerar defrost cruise shut off.

More info, I had the rear tailgate glass replaced because a rear def tab had broken off. I'm wondering if there could be a ground issue. I have no clue what the wiring is like back there and called the glass shop that did the repair.

I appreciate any input, thanks

I would go back to place that replaced rear window and report to them what is going on.

Cruise control turns off when Rear window Defrost is turned on

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