[SOLVED] Cruise control turns off when Rear window Defrost is turned on

[fastscirocco]

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]

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

 

[fastscirocco]

The only LED bulbs I have are back up lights.

 

[Blackcar]

Is that something new the bulbs in backup lights.

 

[fastscirocco]

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]

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]

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]

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]

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]

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.

 

[fastscirocco]

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

I did call them, only person that was there to talk to was the receptionist.
I will report back any new info.

 

[rrosen]

I'll give you a history of my cruise control mysteriously turning off. Probably doesn't apply but ....

Cruise control kept turning itself off. Dealer first said there was a chafed wire by the emergency brake that did it. Fixed the wire but the problem still existed. Dealer had car for almost 3 weeks (maybe longer, it was some time ago). Called in the GM engineers. Eventually they replaced...the radio amplifier!?!?!?!?

Apparently the amp was putting spurious signals on one of the busses (CAN bus maybe?) that caused the cruise control to turn off.

Just a data point for what it's worth.

 

[fastscirocco]

I was getting more issues, cruise would intermittently simply not work, if I kept the window down switch pressed down after it stopped closing it would turn the cruise off. Daughter noticed my passenger's side back up light was intermittently not working. I replaced the GM harness for the lights which fixed the back up lights AND the rest of the symptoms.

 

[fastscirocco]

I'm still having the issue, unfortunately this didn't fix it. It just went a long time without acting up, sorry for the bad news.

 

[petethepug]

If the brake switch fails the cruise control doesn’t work. It can also lock the shifter in Park.

It’s lucky your daughter saw that tail light out. That would be where I would dig in. Remove the LED bulbs until this is remedied. CAN BUS runs off 5v in the system and LED, no matter what’s promised as canbus “safe” is NOT guaranteed. If the dealer had it for 3 weeks and you paid them, take it back without any evidence of you working on it.

Let the dealer use their 2 way scanning equipment to find the bug based on no cruise with defrost and intermittent tail lamp out.

 

[fastscirocco]

I believe I have found the cause of the many electrical gremlins I've experienced, tonight I found a very loose ground wire on the firewall. I cleaned the connection and tightened it. I will be doing over 5 hours of driving tomorrow and will report back afterwards. Background I had recently replaced the brake pedal position sensor and the wiper/turn signal stalk, and continued to have issues.

 

[fastscirocco]

I can happily report the loose ground was the source of my problems. If you are having any electrical issues check all of your grounds.

 

[Fless]

Great! Please add "SOLVED" or "FIXED" to the thread title for the benefit of future searchers.

 

[fastscirocco]

Great! Please add "SOLVED" or "FIXED" to the thread title for the benefit of future searchers.

I can't see how to edit the thread title

 

[Joseph Garcia]

Looks like it has been done.

These trucks are VERY sensitive to electrical issues, absolutely including loose or corroded grounds. When electrical issues arise, particularly if they are random-ish issues/happenings that make no logical sense, it is MOST LIKELY related to a COMPROMISED GROUND CONNECTION.