Just got this awesome 2004 Silverado 2500HD 6.0. Infamous Gauge Cluster issue was known. So, I spent the $300 and bought a new one instead of attempting to install new stepper motors myself.

1. Disconnected the positive battery cable on both the main and auxiliary batteries. Yes - I know now that I should have simply disconnected the negative terminals.
2. Installed new cluster. Simply reconnected positive terminals to both batteries and woolah - the instrument cluster lit up and tested fine.
3. tried to start truck and it would barely run, wouldnt even idle for more than a few seconds.
4. researched here and found that the ECM needed to be reset (simple enough with so many posts here on this subject.
5. disconnected the negative terminals (both batteries) for over an hour and turned on headlight switch.
6. reconnected and the gauge cluster was flashing on and off. I remembered reading that this can be caused by a faulty Headlight Dimmer / Switch. When I switched the lights to off the cluster returned to normal.
7. Then tried starting the truck - same issue, wont even idle for more than a few seconds.

I'm thinking that I need to replace the headllight dimmer switch? Try a different method of resetting ECM?

Thanks for any input. *Truck ran GREAT prior to my disconnecting the battery terminals - so I am at a loss as to an additional way to attack getting it back running!

Greg

 

A 6.0 is a gas engine and should only have 1 battery, so either you have a diesel (6.6) or a previous owner installed an auxiliary battery that may not be needed.

If you have a diesel, the proper battery disconnect procedure is both negative cables then both positive cables; proper reconnect is both positive then both negative. It doesn’t matter which battery you start with.

You may have caused irreversible damage to the PCM (and/or other modules) by disconnecting the positive cables, so I’d recommend checking for codes first, even without a CEL.

To reset all the modules, disconnect both batteries, then connect a jumper wire between one set of the battery cables (positive to negative). Leave it for at least an hour (overnight if possible), then reconnect the batteries, and attempt to start.

 

Thank you for replying. This trUck definitely has a 6.0 Gas engine. When the truck was bought new in 2004, the dealer added the auxiliary battery to handle the plow.

I tried my obd2 to pull any codes... it gets power to the reader, but no input. Checking all grounds... I will also try the reset you mentioned.

I'm hoping I didn't damage the pcm or and other modules.

Greg

 

The only reason I mention the possibility of damage is because GM has issued an ongoing service bulletin since about 2000 that unplugging modules before disconnecting the negative battery cable can cause damage. Disconnecting the positive cable would have the same effect.

Check the following fuses in the under hood fuse block as they supply power to injectors, coils, miscellaneous other components, and the PCM.

PCM 1
PCM B
O2 A & B
INJ 1 & 2
IPC/DIC or SEO B1 (how it’s labeled depends on truck options)

In the fuse block at the left end of the dash, check the IGN 0 fuse.

 

Put in new battery (tested bad), new alternator (tested bad), new headlight switch (tested bad), new low beam relay switch (tested bad).

After replacing the above, the truck would minimally run... after much hesitation I got deeper into the engine compartment fuse panel. Doggone mice had made a mess of the panel. Corrosion was found when pulling out individual guides and relays. I don't have the expertise to remove and install a used upper panel, so is simply removed each guide one at a time / sprayed CRC Electronic cleaner inside the female connectors, let sit and put new fuse in. Worked my way through this procedure until all fuses were replaced. Lifted the upper panel up and sprayed the underside with the electronic cleaner and let it air out. Found 3 wires that needed splicing due mice nawing on them (soldered and shrink wrapped them)!

The trick stayed right up! Let it idle for 20 minutes so the ecm and other modules could go through idle relearn. Then drove it on road (using the basic relearn techniques posted on this forum).

Keep in mind, my obd2 was telling me all kinds of wild expensive things! It taught me to go back to basics! Alternator, battery and other bench tests for switches, relays and shorts. $300 vs $2,000!!

I need to replace the upper fuse panel, if I can find a decent used one. That is going to be an interesting experience when I do replace it.

Anyone with an idea (besides eBay) to find a fuse block?

Thanks for all of the great posted info here!

Body and frame are solid, engine (6.0) is new with only 15K on it). Needs cab corners and rocker panels... think I'll go slip on because i have zero welding experience. Thoughts?

Mice **** under the hay seeds the mice were kind enough to leave!

When you zoom in, you'll see the black wire almost chewed through, but the yellow and grey wires that are twisted around each other just above the black wire - well i don't know what they go to, (any ideas???), but they were shorting out against each other due to bare spots! And yes that's one of 4 dead mice i found.


In the fuse block at the left end of the dash, check the IGN 0 fuse.[/QUOTE]

 

Thanks for the update. Glad you got it figured out.

I’m not sure exactly what the yellow/gray wires run to, but any wires that are twisted together like that are referred to as a “twisted pair” and they are coming from one of the speed sensors. It could be one of the ABS wheel speed sensors, or one of the speed sensors for the transmission or transfer case. The reason they’re twisted together is to help shield the signal from interference from other circuits. When you repair them, try to keep the length as close to original as possible.