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Discussion Starter · #1 ·
I have a 2002 GMC 2500HD crew cab with the 8.1. I was having a valve issue, as well as a lifter, and injector issues with 227k. Came across a deal I couldn't pass up from a friend and got another 8.1 with 74k installed. 45 minutes after picking it up yesterday, my gauges would go crazy, and the battery, ABS, and brake light would come on, intermittently. Last night, it went completely nuts, and I got the added bonus of service 4wd, transfer case trying to go into 4 Lo and 4 Hi on its own, ended up going into a limp mode. I disconnected the positive leads to the batteries, checked the ground wires. I found the firewall to block ground strap was loose on the block, and I rerouted it, as well as adding a second ground. Connected the batteries and all was well for about 5 minutes. Gauges started going crazy again, just not as bad. Wondering if anyone else has had the same issue. I've looked up threads and found simular, but not any with what was actually found.
 

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You installed a new motor, now have ground issues.
 

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Discussion Starter · #4 ·
You installed a new motor, now have ground issues.
This is where I'm lost. I've checked all grounds, cleaned them, and tightened them up. I swapped my alternator out as well. Both batteries are good. I added a second body to block ground just for good measure. Took it back to the shop yesterday and they went through it as well. Today was good for about 30 minutes and then just went crazy again, especially if I hit a bump... I'm still leaning towards ground, but at the same time, it can't be. On a good note, trans hasn't acted up and I have lights that weren't working, now working again.
 

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It could be some wire/connection got damaged, so when you hit a bump, the connection breaks for long enough to screw things up, and then when you stop and wait, it settles back to making a good-enough connection.

Maybe wiggle the wiring harnesses while parked and see if the problem happens.
 

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This is where I'm lost. I've checked all grounds, cleaned them, and tightened them up. I swapped my alternator out as well. Both batteries are good. I added a second body to block ground just for good measure. Took it back to the shop yesterday and they went through it as well. Today was good for about 30 minutes and then just went crazy again, especially if I hit a bump... I'm still leaning towards ground, but at the same time, it can't be. On a good note, trans hasn't acted up and
lights that weren't working, now working again.
I’m a visual learner. This is the fuse box.


Green is headlights, red is rear, black is PCM, white is body. Four completely separate and independent wiring harness. Expect for the main ground and power.
 
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Discussion Starter · #7 ·
I’m a visual learner. This is the fuse box. View attachment 875435

Green is headlights, red is rear, black is PCM, white is body. Four completely separate and independent wiring harness. Expect for the main ground and power.
One update I have is I pulled the gauge cluster and spliced into the ground wire to the ECM ground wire to the dash frame. All of a sudden, no gauge issues the rest of yesterday. This morning it's back, but only if I quickly accelerate. That is the fuse block under the hood, correct?
 

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Discussion Starter · #8 ·
PROBLEM HAS BEEN SOLVED, AND I RECOMMEND ANYONE WITH CLUSTER ISSUES TRY THIS FIRST! My original fix of bringing the ECM ground wire going into the cluster straight to the dash was right on point. However, when I did it, I cut and stripped the wire (black/white going into harness position A8) and tied my new ground wire into both. I believe I created a loop. I went in this morning and rewired my new ground straight to the end going into the harness, and removed the wire to the original ground. Just drove over 100 miles, and the problem has not come back.
 

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Discussion Starter · #10 ·
thanks for coming back and posting what fixed it for you.
I can't stand when nobody comes back. Like, did you figure it out??? I knew it was a ground issue, just didn't know where. Everyone was saying cab ground. I've been through then all. Then it's stepper motors or a new cluster. My gauges were dancing all over the place, or weren't working at all. I've done the new cluster thing and it worked for a bit on previous trucks. My question is, could a 5 minute placement of a ground wire fix their problems too? 🤔
 

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I've got a 2012 GMC sierra Z71 4X4 with an intermittent loss of communication to the BCM. When this happens quite randomly (most frequently going in reverse in my driveway after a 20-25 min commute but not every day and then most the time if I'm driving for 1 1/2 straight but sometimes I'll go on a road trip for a weekend and never have the issue arise).

When it does go out I do get a crazy dash gages going offline and online again, if I'm in the middle of a road trip and don't stop the TPMS light will stay lit until I shut it off and restart it.

I'm wondering if your fix for your 02 2500HD might be the same for my 2012 GMC sierra 1500?
 
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