1999 GMC Sierra - Cluster Won't Work w/o Code Reader?

[Holly]

Instrument cluster will not work without code reader plugged in.....customer had transmission replaced by a friend...has had problem ever since. No wires pinched. Don't look like they are related.

[steven kiser]

MMMMMM, if I had just to shoot from the hip here it seems the reader is back feeding the cluster which would lead me to look for a blown fuse, broken ground wire or one that wasn't reattached. Very high probability of feedback. The other issue is if the key was on the on position when the battery was either disconnected or reconnected it may have spiked the pcm. The friend that installed the transmission may have done a boo boo and is being tight lipped. I would plug in my scanner and take a good look around. You may find the scanner will not communicate, wouldn't really surprise me. Look at All the fuses with key on and parking lights on, also keep an eye out for any missing fuses, something I've run into from time to time, when I'm on a search and discover mission I have a jumper I made that I pop into any open fuse slot that has two female plugs in it. Most blank fuse receivers have only one side with a female receiver in it. Oh, remove the reader before checking fuses, with it installed and finding a blown fuse, you will get a false positive on the blown one unless your reading amps then you'll see a difference. I'll end with this if you turn the key off, disconnect both battery cables you may see signs or arcing leading to a blown pcm, just make absolutely sure all the fuses are good. Not 100% sure on this but if you remove the cluster you may see the blow out in the grid work. This will remove any doubt. However I would warn the customer that the issue that blew the cluster may still exist. If you have a mind to you may try to bridge the blow out with a wire strand and super glue just to see if it will blow out again. Just one more think then I promise I'll stop, see if the alternator is overcharging. This is another point for a spiked pcm.

[Jeff @ Able Auto]

Cluster shares ground with data connector at right rear of engine. This is also ground for cruise module and maf sensor. That's where I would look first.