2002 Tahoe Electrical Issues

[ScottyBoy]

I just had a very similar situation on my 2001. But my engine would still start and run, that being the big difference. It was acting like I had a low/dead battery or else lost a main ground wire. When I turned on my headlights, there was a faint humming/buzzing sound coming from the dash. Almost like the headlights on chime, or key left in ignition chime, but at a much lower volume and a lower tone, kinda like you would think it would sound if the battery was almost dead. I had a bunch of warning lights on my dash, turn signal indicators were both steady lit (but dimmer than normal), the fuel gauge was at zero even though I knew I had a full tank, the low fuel light/message would flash on the gauge cluster, along with weird messages like low coolant, check oil level, etc. None of my power locks, seats, or windows were working. Although you could hear the locks in the doors faintly engage when I pressed the pwr lock button. Again, they sounded very weak, like I had a dead battery. I had relays everywhere chattering like they were trying to click on and off but weak, like the battery was dead. Relays pretty much everywhere we're chattering like that, under the hood, in the dash, and even in the rear AC unit area in the rear passenger side panel.
I don't know what caused all of this as everything was fine until I jumped my AC low pressure switch on the AC accumulator as I was trying to recharge my air conditioner with refrigerant. I was jumping in to force the compressor to come on so it would start taking in the refrigerant. But right after I jumped that switch, I turned the AC control panel to high and that's when everything went to hell.
I still don't know what EXACTLY happened. I had my mechanic look at it and he hooked up his Autel bi-directional code reader and reset or reflashed all the computers/modules. I'm still not 100% sure what all he exactly reflashed, but after he did that, EVERYTHING went back to normal and started working again. I'm just glad it was a simple fix, cuz I was scared I fried my BCM or something.

 

[rockola1971]

If tranny has been recently removed check for pinched wires in between tranny and engine block. Does the starter sound healthy (normal) when the engine is cranking over?

 

[ScottyBoy]

Also, I didn't even mention this because I just assumed you already checked all this: But if you didn't, you need to check the battery voltage with a voltmeter. Check all the battery cables to make sure they are not loose or corroded. Don't just shake them to see if they are loose, unhook them from the battery and closely inspect them and clean it needed. Side post battery terminals can be deceiving as far as hiding thick green crusties under the battery terminal. The rubber boot hides it pretty well, and you can't see it until the battery is disconnected. Check the grounds on the engine and frame.
Usually these are the very first steps you take when troubleshooting a no start/weak start issue, so I didn't even mention it because I just assumed you already did all this.

 

[Rocket Man]

Have you tried a new battery? Sometimes they text good but cause all sorts of electrical gremlins. I didn’t see any mention of battery.