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Discussion Starter · #1 ·
Hello not really sure if this is where I should put this, but it is electrical related, so here goes.....
I have a 2008 GMC Sierra 2500HD extended cab 4x4 manual windows and door locks LY6 6.0 liter, OK my problem is when I Put it in drive to start driving the transmission hard shifts from 1st to second then the RPM and Speedometer gauges go to the off then on and off position" fluctuating on and off" and it doesn't shift till the gauges turn back on and stay on, also while the RPM and Speedo are off the ABS light turns on, Im wondering if anyone has had this issue and what they did to solve this issue.
 

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Discussion Starter · #4 ·
I have checked all grounds in in it , No loose connections I will be doing a change over to 1/0 Gauge Positives and negatives prettey soon, but Im trying to fix what ever this issue is at the moment I had a Mechanic tell me its the body module which the was a Canbus connection Trouble code when running the codes through a Tech2Win GM diagnostics program.
 

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Discussion Starter · #5 ·
also My heater controls work intermetently work some times but dont work 99% of the time , when I say heater controls I mean the hot/cold and defrost/vent selector knobs, the fan knob works all the time.
 

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2004 Sierra 3500 6.0L, auto, extended cab, cab&chassis, upgraded to 4wd
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First, there are a bunch of power and ground connections to the ecm and the various other computers. The full service manual (FSM) will list all of them and where they are... Did you use the FSM to find "all" of them, or some other list, or just what you could see?

Second, you need to know the exact code to then get the diagnostic procedure to find out where the problerm is and how to fix it. And the FSM also has all the codes the truck can generate, and the diagnostic procedure for each one of them to figure what is causing the code and how to fix it (as it's not just "you got this code, you replace this part").
 

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Discussion Starter · #7 ·
I do not have a factory service manual I only visually tracked known grounds like (battery to body) (body to engine) (body to frame) ect. I am using a digital multi meter to test if the ground is a proper ground with 0 resistance.
 

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Discussion Starter · #8 ·
an other thing I noticed is that the engine does not stall when this problem occurs which tells me its not a ground issue at the PCM,.....now there is a purple wire that is in the bundle next to the relay box under the hood that was tapped in to for some reason (dont know what the wire goes to) that I had to resplice back together, "old fleet truck's, where the companies are to cheap to fix them right so they rig'em"
 

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2004 Sierra 3500 6.0L, auto, extended cab, cab&chassis, upgraded to 4wd
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Just ohming across the connector may not be enough, as that uses only a tiny amount of current to check the resistance, while when more current is passing through while the truck is running may show a voltage drop across the connection.

And access to the FSM via a site like alldatadiy.com is relatively cheap, particularly if you plan on keeping the truck for some time and want to repair or at least diagnose problems yourself.
 

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OP, As Dave has mentioned, these ECM's don't take much too mess with them, and there are a lot more grounds than just the big ones. let us know how it goes.
 

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Discussion Starter · #11 ·
dave how cheap is ,cheap , with a person with no spendable income its kinda hard to purchase anything, Especially with SSI where you can only pay for rent and food and nothing else. I am disabled but its not "disability" no useable income makes it hard and I cant earn any income or they will take away my SSI
 

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2004 Sierra 3500 6.0L, auto, extended cab, cab&chassis, upgraded to 4wd
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Well, you can go to the web site and see for yourself how cheap is cheap. And I guess I pity the person who has a similar truck that happens to park near you when you need parts...
 
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