Truck stuck in unknown driver mode after jump start

Tiny
MANNYT18
  • MEMBER
  • 2006 GMC SIERRA
  • 6.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 197,656 MILES
Truck listed above is a 500 crew cab Denali. I believe my truck might be stuck in unknown driver. All electrical in truck like; door locks, windows, and cluster gauges stopped working except tachometer. Truck starts and stays running. Also no communication to my obd2 scanner but will power up. All this happened after a jump start. Any help would be appreciated.
Saturday, July 24th, 2021 AT 10:46 PM

13 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
More than likely you have a fuse issue but here is a guide that will help with this issue:

https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked

I attached the info below on the fuses so let's use a test light and turn the engine on and check each fuse and make sure you have power on both sides of all the fuses. I suspect a BCM fuse is going to be the issue.

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

Please let us know what you find with this. Thanks
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Sunday, July 25th, 2021 AT 7:07 PM
Tiny
MANNYT18
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Checked them all, they all have power to them.
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Monday, July 26th, 2021 AT 3:04 PM
Tiny
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If you have no fuses that are blown then it appears we have a bus corruption issue that is preventing the cluster from communicating and your scan tool from communicating with the ECM.

Is there any chance that this vehicle was struck by lightening?

The only reason is, this is odd as these things are not on the same network so I am not sure what would cause this but we need to start with checking voltage on pin 6 and 14 to ground for each.

These are the two pins that directly communicate with the ECM so if you are getting the tool to power up then you have power and ground but we need to find out what voltage is on each of the communication lines.
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Monday, July 26th, 2021 AT 7:25 PM
Tiny
MANNYT18
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Well, after the jump start the only fuse I found that blew was the radio fuse. I replaced it but is still didn't do anything. RPMs is the only gauge working on cluster, battery light stays on all the time and ABS. And it doesnt show the range. It shows odo, hours on engine, and language. Dome lights stay on and don't turn off. I did test light fuses and this is what I found
No power to these fuses.

Engine fuse box
PR Defog
Crnk
Fog lp
Rh hid
Lohdlp-rp
Lohdlp-lt
Hihdlp-rt
Hihdlp-lt
Frnt prk
Lh hid

Side dashboard fuse box
Rr wpr
Ws wpr
Veh stop
Brk
Lcks

As well the battery will drain overnight if left connected.
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Monday, July 26th, 2021 AT 10:17 PM
Tiny
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So this is critical to double check because if you have only a select number of fuses that do not have any power at all on either side of the fuse then this means the fuse blocks have failed and you have open circuits on them not supplying the power to these fuses. Clearly if the other fuses are working then we have 12 volts getting to the box but it is worth checking and making sure this connection is tight.

When you jumped the vehicle, is there a chance you put the cables on backwards? Basically it is highly unlikely for one of these fuse panels to fail but to have two of them, is unheard of.

So if you have no power to these fuses then we have an issue from where the power comes into the panel and the fuse which means we will need to replace these panels.

Let me know if I am not understanding correctly. Thanks
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Tuesday, July 27th, 2021 AT 6:41 PM
Tiny
MANNYT18
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I haven't checked voltage on the B+ pillar, but on my test light, it does light up. I had the truck in the on position, and my bro in law was messing with the cables and he had touch the right front fender with the negative cable. I had saw sparks come off that spot he touched, and that's when everything stopped working. Ill check for voltage on the b pillar again and let you know.
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Tuesday, July 27th, 2021 AT 7:03 PM
Tiny
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Oh, okay. Yeah. These are normally more faulty tolerant then that but those sparks clearly shocked the electrical system and more then likely the circuit boards of the panels have failed.

So while it is still rare, it appears this is the issue. If you don't have power on fuses but do have it at the B+ then the issue is between that post and the fuse which is only the circuit board of the panel.

If it were me, I would be replacing these panels and move on. If you want to test it more, you can take your test light and jump 12 volts to these fuses one at a time and see if the system comes back online. Just touch one of the posts on the fuse and it should work. Put your test light clip on battery positive and then use the probe to jump it.
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Tuesday, July 27th, 2021 AT 7:15 PM
Tiny
MANNYT18
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I couldn't figure out my problem so I pulled the PCM. I noticed some cracked soldered joints during inspection. I don't know what these power but i'm pretty sure they're not suppose to be cracked.
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Friday, July 30th, 2021 AT 8:44 PM
Tiny
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I don't see that this would cause the fuses to not get power as the fuses are feed directly from the battery through the fuse box. However, these joints should not have cranks in them so that would definitely need to be fixed.

It is hard to see in the picture but those appear to be solder joints so just heating them with a small tip soldering iron and adding solder if needed should take care of it.
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Sunday, August 1st, 2021 AT 10:52 AM
Tiny
MANNYT18
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Turns out PCM is fine. Glad that didn't get damaged. So decided to have cluster inspected and found that the cluster got burnt out. In the very corner the display got burnt, and the clusters smells burnt really bad. Not sure if getting this fixed will solve all the issues im having.
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Monday, August 2nd, 2021 AT 6:00 PM
Tiny
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Wow, great find again. Is there any chance that this was hit by lightning? It is just odd that you would find multiple issues like this.

Clearly that needs to be repaired but I am pretty sure that will fix the cluster related issues.

Let us know how it turns out. Thanks
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Monday, August 2nd, 2021 AT 9:01 PM
Tiny
MANNYT18
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Alright moment of truth. Traced it back to a bad ABS control module. I started disconnecting modules one at a time and starting the vehicle to see if anything would start working and sure enough when I disconnected the abs control module everything started working again. Cluster gauges, windows, door locks, radio, everything. I had learned that all those modules are on the same communication line and if one of them has a bad circuit, it'll disrupt the communication to the other modules. Somebody had told me to do that and sure enough I traced to the ABS, and prior to that I had just replaced the ABS control module a month ago! I'm sure glad I figured it out, now I got to find a new module.
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Tuesday, August 10th, 2021 AT 5:11 PM
Tiny
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Okay. That is a great job. Yeah that is the bus communication issue that I was mentioning prior. I should have pushed that harder but I got off on a different path however, the fact that you found the ABS bringing the bus down the bus points to again a traumatic event like a power surge. ABS modules can fail and cause this just from being worn out but that is less likely.

Here is a guide that talks about this but the network in the GM world is called GMLAN and the interior bus is called Class 2:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

However, this all makes sense no that we have the answer.

Great job again. Thanks for updating us.
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Wednesday, August 11th, 2021 AT 2:10 PM

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