Cruise control is not working - Cruise control wiring diagrams

2006 CHEVROLET SUBURBAN
176,000 MILES • 5.3L • V8 • RWD • AUTOMATIC
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PENZFAN
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Hey Guys. The cruise control stopped working a year ago so I replaced the fuses, brake light switch and steering column wiper/turn signal/cruise lever. It did not fix the cruise. And there are no codes when I check with the code reader. This weekend I hooked up a U-Haul trailer to move some stuff and the cruise control worked again all day while the trailer lights were plugged in. I used a 7-pin adapter to plug the 4-pin U-Haul lights into. After I disconnected the U-Haul the cruise stopped working again. I plugged in the 7-pin adapter thinking that may have had something to do with the cruise coming alive, but no luck. Is there some type of load sensing switch that controls the cruise control under a load? I am stumped! Thanks
Dec 31, 2016 at 5:27 PM
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STEVE W.
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Nothing like a load sensor for the cruise. Did you happen to notice if the cruise only worked when you had parking lights on?
If you have a trailer brake controller you might try unplugging it from the fuse box and see if the cruise works then. Maybe it is feeding just enough voltage into the brake light circuit to make the cruise think you are stepping on the brake and shuts the cruise off?
Dec 31, 2016 at 10:10 PM
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PENZFAN
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Hey Steve. Did not have the lights on at all while the U-Haul was hooked up. I do not have a trailer brake controller either. Tried it again last night after dark with all lights on and it still is not working. Odd that it only worked with that U-Haul and trailer lights hooked up.
Jan 1, 2017 at 10:11 AM
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MHPAUTOS
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sounds as if there is a problem in the trailer brake light circuit or the plug is not wired to suit your car. check this out and make sure that it has not blown the brake light fuse on your car as well.
Jan 1, 2017 at 2:19 PM
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PENZFAN
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Thanks MHP. The cruise was working fine for nine years and nothing changed as far as the OEM trailer light plug. I will check to see if maybe there is a ground issue at the trailer light plug. Brake lights and fuses are all fine and no codes when I plug in the code reader.
Jan 1, 2017 at 5:31 PM
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MHPAUTOS
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Good thing to prove that the plug is okay, then work back.
Jan 1, 2017 at 7:23 PM
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STEVE W.
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Penzfan, I was talking to a couple other techs about your problem. All of us came to the same conclusion. It did what! :-)

I do have a strange test. Try pulling the CHMSL fuse out of the lower fuse panel and see if your cruise returns. That is the circuit that feeds the trailer brake lights and tells the PCM to shut off the cruise control. Perhaps some corrosion or something could be causing enough current flow to shut the cruise off (just like stepping on the brake).
With the the light converter and the trailer that may have created enough of a load to stop that current flow and the cruise turned back on.
Jan 2, 2017 at 10:06 AM
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PENZFAN
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I pulled the CHMSL and Cruise fuses, cleaned the terminals and reinserted them. Cruise did not work. Should I try it with the CHMSL pulled out? Thanks
Jan 3, 2017 at 2:13 PM
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STEVE W.
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Yes, pull the fuse and see if the cruise works. Just trying to eliminate any odd thing that would turn the cruise off externally. The CHMSL fuse is the feed that shuts off the cruise when you step on the pedal. May do nothing but it will eliminate one possible item. Then I can go back to the drawing board.
Jan 3, 2017 at 2:43 PM
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PENZFAN
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Hey Steve. Tried that didnt work but guess it eliminted that element. ????
Jan 4, 2017 at 8:08 AM
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STEVE W.
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Yeah at least is drops one item off the list... Back to pulling more hair out...... I'll dig around some more.
Jan 4, 2017 at 9:49 AM
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PENZFAN
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Thanks. Ive plugged the 7 pin adapter and 4 pin harness back into the trailer light socket to see what if anything that does
Jan 4, 2017 at 11:34 AM
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STEVE W.
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If the cruise starts working maybe get a short extension harness (cheap one, as it's going to get cut). Then cut each light feed one at a time. When you cut the one that stops the cruise from working post it here. Along with the make model of the adapter. Maybe it's a diode or feed in the system that is letting it work, like a better ground or ?????
Jan 4, 2017 at 5:52 PM
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PENZFAN
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Well, tried it with the harness with everything grounded and not grounded. Didn't trigger the cruise to work.
Jan 6, 2017 at 11:09 AM
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STRAILER
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Hey PENZFAN,

It sounds like it could be the switch, here is a wiring diagram and guide for you to start testing the system.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Please run some tests and get back to us so we can continue helping you.

Best, Ken
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Jan 9, 2017 at 2:03 PM
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PENZFAN
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Thanks for the feedback and diagrams Ken. Do you mean the turn signal/cruise/wiper switch? Because that has been replaced. Where should I start testing the circuits?
Jan 9, 2017 at 4:25 PM
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STEVE W.
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OK here is a possible item. Talked to a GM engineer about this, he said that the system won't activate if it detects the wrong resistance from the bulbs. This might explain why it worked with the trailer plugged in. The trailer lights added enough resistance to make it work. He said they have seen this with LED replacement lamps and with some brands of bulbs. I'm wondering if you have a similar issue. I can't think of a way that resistance would drop in a common circuit though, usually it's a case of higher resistance.
Jan 9, 2017 at 5:25 PM