2006 Yukon possessed by the devil does whatever it wants

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TYF Newbie
Aug 28, 2023
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So I am trying to help out a Disabled Nam Vet and he needs help he is a really great guy someone I used to tend bar with 30 years ago. He knows nothing about cars and just purchased a 2006 Yukon after saving up his disability check after paying bills for a year. He drove the truck up to my house he lives about 45minutes from me and he was saying he had no AC which I told him I would fix for him no problemo. Like I said Jimmy is a great guy and doesn't understand a thing about cars or computers or anything in this realm. I asked him what was going on with the AC and he said "it just blows hot I have 2 cans of refrigerant I put in and it still blows hot plus I cant shut off the fan in the back or turn on the fan in the front. So I asked him to go grab an alcohol free beer and have a seat I really didn't want him helping as I know he will break something or hurt himself. I have been trying to get him to stop slamming doors shut and go easy on things for 2 decades but he is very ham handed he broke the door handle on my Denali twice and already broke the hood open latch on his new truck the first day he had it so enough of the background story now for the repair part.

I start the Yukon find the blower switch for the back show him where it is and how it works so problem one solved AC is blowing hot so I check the AC and the clutch is not engaging at all so I figure low refrigerant. I get the can he has been filling it with for the last 2 days and show him what the safety ring is on the can then remove it and fill the empty AC system to its proper level the AC clutch is now engaging and its blowing cold. I figure we are done no big . The next day he calls and tells ne its not working the fan in front wont turn on anymore. I get the truck and sure as sh%t it is no longer working I put a meter on it test the blower motor check the fuses and order a new resistor. I get the new resistor put it in turn on the ignition the blower now works fine but the head unit is no longer lit and now we have ABS , TC, and engine lit on the dashboard. I turn it on and off sometimes the head unit comes on sometimes it does not Im pulling fuses and checking wires restart the truck and its fine everything works then the truck just shuts off no engine running, headlights are on and bright so I restart the truck and its running fine but now the AC is no longer blowing cold. I figure I need to recalibrate the AC\Heater actuators so I do the fuse pull wait one minute put it back bla bla bla so now everything is working but the head unit is not lit. I told him to take the truck home give me some time to order a flee bay head unit and do some reading on this truck.

By now Im thinking GROUND STRAPS so I tell him to bring in up to my house the next day and he tells me he has no transmission it died on the side of the road and he had to pay 200 bucks to get it towed. I explain to him how much AAA costs and I cant trouble shoot a tranny problem from my armchair we decide I will use my AAA to tow it to my house I was thinking maybe a valve body who knows so before he has it towed here is what it does. It wont go into park the shifter is in park but the truck still rolls. If he try's to put it into drive it grinds very loud, neutral is fine, no reverse.
SO I have him start the truck then put it in neutral and push the 2wd button . The transfer case shifts into 2wd and now all is fine the truck drives the AC works the head unit is now lit . In neutral it flashes SERVICE STABILITY CHANGE OIL SERVICE AIRBAGS on the dash ABS is lit engine light is lit and TC light is on.
WHAT do I do next I figure check, clean, replace all ground straps maybe pull the fuse box clean and spray with dielectric spray. OK so ANY ideas on things IM not thinking about or doing wrong please let me know so I can get this guy back on the road ...

I will check codes when he brings the truck back up here. I did check them the first time but there were no codes on my cheap 25 dollar OBD2 reader. All these problems and no codes??? gotta be ground straps???/???
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Supporting Member
Feb 16, 2018
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Richmond, VA
Quite a story! Good on ya for trying to help a friend - and a disabled vet at that. Please pass along to him that the folks here on TYF (I think I speak for pretty much everyone here when I say this) thank him for his service and sacrifices for our freedom.

You might have more luck posting this in the 2001-2006 section, but o summarize, it sounds like you have a truck that will run and drive now, the A/C is cold again, but the dash is lit up with all of the warning messages you mentioned. Is that right?

If so, we're going to need to get all of the codes currently present. Be sure to use a code reader that can read all of the modules for a 2006 GM car, including not just the ECM, but the BCM and all of the other bits.

Joseph Garcia

Supporting Member
Aug 2, 2018
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^^^^x2^^^^ Need to get a good bi-directional scanner to get to the source of your issue(s), or you will be firing the parts cannon at it.

Good idea to check the grounds, though. Engine, chassis, transmission grounds.
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Staff member
Super Moderator
Apr 2, 2017
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Elev 5,280
Moved you here to the correct year forum.

Check and clean the engine and body grounds. I'll attach a PDF with the ground locations (from the upfitters' guide). The PDF is zoomable.

Most important grounds are:
On the left body mount (near the frame) just behind the left front tire (ground zone 18 & 21a & 21b)
One of the main engine to body grounds behind the driver's side head, to the firewall (GZ 8)
The ground at the left front on the engine block (GZ 3)
The ground on the radiator crossmember (follow the smaller ground wire from the battery)

Also check both the positive and negative battery cables for internal rot.


  • Grounds - GMT800 Body Grounds Unmarked.pdf
    60.9 KB · Views: 14


Mar 18, 2022
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COlorado Springs CO 80908
Hope you got the vets' truck right? I had a similar issue - my 2001 Yukon XL was possessed with weird fault codes that kept changing. The PCM was also humming like crazy and it turned out to be the bolt was loose at Ground Zone 3 at the Front Engine Block. I also moved/replaced the ground strap behind the oil sensor (Ground Zone 5 (what a stupid place) ) to a better spot on the firewall where it was easier to test to the battery.


Full Access Member
Dec 29, 2016
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Indiana (formerly IL)
Definitely sounds like a bad battery or grounds and/or neg or pos wire connection problem. Id clean all grounds of corrosion and check battery out and connection at battery and that annoying positive between the fusebox and engine. Also verify the tranny shifter cable and its bracket at tranny is not loose or out of adjustment. Our generation of K chassis are notorious for getting wacked out when a loose, corroded or broken ground is in the picture and the craziness depends on which ground(s) has a problem.