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Discussion Starter · #1 ·
I think my Grandsons truck is haunted. Here is a list of things that suddenly went out. The HVAC, Fuel Gauge, Cruise Control, 4WD, Heated Seats, Odometer, Oil and Temperature Gauges all went out. He said one day he accidently hit the washer switch and everything came back on, but went out again a short time later. I don't know if that has anything to do with it or not, just trying to fully describe everything he told me. Could it be a loose ground or something?? :?
 

· US Navy Vet, TOTM, Law Enf ret.
2015 Sierra SLE 5.3 4x4
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Did he hear any voice telling him to "GET OUT!" ?

If his head starts spinning and he pukes up pea green soup, I'd say it's time for a nice new GMC Sierra.
 

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Discussion Starter · #4 ·
He traded some kid even for a 1999 dodge diesel he had. I know that kid took it off road because it had dried mud all over it. But this problem didn't start until he had it for a few weeks. If he did take it off road, he hasn't said anything about it.
 

· Supr Moderator AutoTech SS-Guru Mbr Extraordinaire
2015 High Country Duramax
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When my alternator was dying, it made the truck do all sorts of weird things. Lights would flicker, gauges were reading weird, it even seemed to shift different. It also gave me a service 4wd light a couple times.

All this while it was still putting out 14 volts. But then one day it just totally stopped putting out anything. And output voltage isn't the whole story with an alternator. I have a feeling mine had some ac leakage which is why things were going whacky.

Just something to look into. Also, depending on the year if this truck, the gauge clusters on the 99-07c trucks aren't known to be the best. Especially the 03-07c trucks. The stepper motors go out and the gauges are either stuck or won't read right/at all.
 

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Only times I have seen things to this extent is when the truck has been in deep water. Seen it on my buddy's F150. Another buddy's ram 1500. and few people on here with their trucks after they went off road. My alternator on my truck just went out 2 weeks ago. just up and quit. wasn't causing me any kind of issues. But it has been known to happen. Just not like this. I would dig into it and see if he doesn't say something to the affect of he took it off road.
 

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Discussion Starter · #8 ·
He left the truck with me until I can check the things suggested by you fine folks. He said he run it through some mud puddles then it started acting up a couple weeks after that. But lo and behold my starter went out across town so he got his truck back and I'll have to put a starter on mine!
 

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Gotta love how that works. Since it has come to light that the truck has been in mud and water. I would be taking off ground connections cleaning them and make sure they are back on tight. Also unplug any control modules and clean out connectors. Hopefully the ECM hasn't been effected.
 

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Good time for the Grandson to learn some wrenching. He will obtain the knowledge to maintain his vehicles and the common sense to not abuse them so much. (teach a man to fish)
 

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Discussion Starter · #11 ·
I'm trying to teach him a little as I go. How would one go about checking the Alternator for stray voltage? I'm assuming it should be running. From there do I go from alt. case to ground. from case to battery or another way. The alt. is putting out 14+ volts. Today he brought it over and I disconnected the neg. battery cable for about 45 min. when I hooked it back up the gas gauge went completely clockwise and his speedometer stopped working. This thing truly is haunted!
 

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Discussion Starter · #12 ·
We broke down and took it to the gmc dealer and had it scanned. An 8:00 appt. at 2:00 they scanned it, said it was an aftermarket security system. He doesn't HAVE an aftermarket security system. Anyway...I'm leaning toward a bad or loose ground.
 

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Does it have an aftermarket remote start? If so that may be what they are talking about. Any loose wiring under the dash, splices etc? Did you check the ground to the control module?
Check DC voltage between neg battery terminal and each ground while running. As previously stated the alt could also cause problems. Especially if it has a bad battery, under a load from bad wiring bad fusible link etc. Does the link (small cable from the the alt) Get extremely hot? Alt get very hot? If you can read voltage (>0.1 or 100mV) between the lug on the alt and pos battery cable I would disconnect the alternator see what happens. Be sure to unplug the connector and the ring terminal and have the terminal insulated. If you replace the alt be sure to check the fusible link and connections as it may overload the new alt and need to be replaced as well.
 

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Discussion Starter · #14 ·
I texted him and it doesn't have an factory or aftermarket remote start. But it looks like some more good information for me to start on. As always, thanks for the info & let me check this out and I'll get back with everyone.
 

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I'd also lean to an alternator issue but since this happened after mudding I wonder if something is shorting out? Try running the truck at night to see if you can see anything visibly shorting out. Look for loose/frayed/worn wires and listen for the clicking of a shorted wire
 
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