GMC 1500 HD electrical short in IGN 1 circuit, need troubleshooting help! - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 08-07-2014, 10:17 PM   #1
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Default GMC 1500 HD electrical short in IGN 1 circuit, need troubleshooting help!

Hi all,

I have a 2002 GMC 1500 HD. Since the last time I drove this truck, a mouse tried to move in behind the glove box. I evicted the unwanted tenant, but I fear he may have nibbled some wires. When I went to drive my truck after he showed up, all of the gauges were completely dead, but the truck still ran and drove fine. I was able to monitor my speed and other information through my Scan Gauge, so I know all of the sensors were working properly.

I found the IGN 1 fuse was blown, which supplies power to the gauges. I replaced the fuse, and tried to start the truck. The IGN 1 fuse also blew again instantly, as soon as I turned the key the 1st time after replacing it. It also started and immediately stalled, and repeatedly did that with about 5 more attempts.

Then I got out the meter and tested for shorts. The ignition switch (supply) side of the fuse was at ground potential with the key off, and +12V with the key on. The load side of the fuse was at a short to ground regardless of key position (checked with the fuse out of course).

I then pulled up a circuit diagram and found that the BCM and instrument cluster are fed off of this circuit, so I completely pulled and unplugged both the cluster and all 3 connectors off the BCM. I retested and still measured a direct short on the load side.

I was able to connect my AutoEnginuity scan tool and communicate with the BCM and also to perform gauge sweeps on the cluster (with the blown IGN 1 fuse?!).

I do not have a wire routing diagram, so I am not sure where to continue my search for the short, lest I pull the whole dash apart and try and manually trace it, but I am hoping somebody might have a suggestion on where to go to next without that extreme of a solution (or at least a specific harness and route to follow). Or even a suggestion on something to test or check that I have not thought of to this point.

And I am hoping that once I resolve this short it will also resolve the start/stall problem it seems to have created, lest I move right into that issue next.

Thanks for any help!
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Old 08-08-2014, 08:28 AM   #2
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you know the fuse blows and the mouse ate some insulation a off the wire some where. i would cut the wire after the fuse and solder in new to everything it powers. i dont have any diagrams. they might have it on autozone or you might have to pay for a oem manual for it.
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Old 08-10-2014, 06:00 PM   #3
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I was really hoping to find the damaged area, if for no other reason that to be sure no other wires were also damaged. I am also unsure if anything else is on that circuit other than what I have checked. I am going by the wiring diagram I had, but I have also seen things that allude to the oil sensor and/or coolant temp sensor being powered somehow by that circuit as well. I do not know if this is true, as I was obtaining readings from those sensors while the fuse was blown.

I am hoping to find the root cause, and not just circumvent the problem. In part because I am not 100% certain the mouse is the cause, it is just very coincidental at this point, and although it sounds likely, it is not the first time I have had a mouse take up residence in the truck (I live in a heavily wooded area where field mice are rampant). It would however be the first time they tried to nibble wires instead of just the stack of napkins I leave in the drivers door pocket.

Thanks!
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Old 08-11-2014, 08:37 AM   #4
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you will have to to take the wire out of the harness the whole way if you want to find it.

some peanut butter with mouse traps i have found works good, and no food in the car
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Old 08-12-2014, 11:47 PM   #5
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Look under the fuse block in the engine compartment. Mickey likes to live there.
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Old 08-17-2014, 09:02 PM   #6
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For what it'* worth, and because I always hate it when threads with a mystery are never updated. I finally finished repairing this today. It took me a few days of troubleshooting (after work, and hour here, and an hour there kind of thing) to find what harness the short was in. It ended up being in the headliner harness, when I unplugged the headliner from the Relay Block (left of the brake pedal, by the firewall) the short went away from the fuse. I was able to probe the connector to find there were at least 2 shorts in the harness, so I followed it up to the headliner, where I found the remains of another mouse nest almost directly behind the visor, above the drivers head.

I pulled the drivers side corner of the headliner down by removing the visor, A-pillar trim, and center overhead console. That allowed me enough access to shop vac out the nest and repair all of the wires.

I also took the under hood fuse block out and found some apparently older damage there, and repaired that too. I searched real good under the dash for any more damage, and could find no other problems.

The truck starts right up now and everything is working like normal again. But for the life of me I cannot figure out how a short in the headliner harness would prevent the truck from starting (I unplugged the harness, replaced the IGN 1 fuse, and tried to start it, it still started and stalled and reported the BCM did not supply the fuel continue signal. The fuse did not blow with the headliner harness unplugged).

But with the headliner harness repaired and plugged in, it starts perfectly. Mystery to me, but glad to have it working and mouse free again.
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