Sorry I should have been more specific, try to connect pin 5 in the OBD connector to battery ground as a separate test. Connecting to the engine tests one ground path, the OBD connector tests a different one. Thinking of it, HeyYou's suggestion to jump pins 4 and 5 should work too.

My thinking as well, actually you probably answered your own question as the scan tool probably connects pins 4 and 5 internally as they are both grounds.

 

Yep, that's what I was thinkin' as well.....

 

So everything I've been reading and by your thoughts and suggestions I'm inclined to believe it's a ground issue even though I have brand new braided ground straps from battery to frame and cab and 4 new straps from cab to block and pcm. There's a ground somewhere causing issues. Even removed the battery tray and there's several smaller grounds at two locations (1 near drivers headlight and one under tray) all showed 12.4v. I will keep digging and see where the problem is.

 

By jumping pins 4 and 5 on OBD2 would that tell me where the ground issue is or just showing there is one?

 

That would tell you the ground issue is with that particular circuit from the PCM. (pin 31 and 32 on the PCM connector, I think.) Those hit a splice, and then go to ground together. If shorting pins 4 and 5 on the diag connector makes things work as they should, then that ground circuit IS the problem.

 

Understood. Might not get to it today since it's snowing pretty good, but will get to it tomorrow and report back. Thanks for the help!

 

The ground issue is likely the ground connection at the front of the engine or the wiring from the PCM to it. You already checked the ground from the engine to the battery when putting a temporary wire in between.

 

All grounds connections were good. Jumping pins 4 and 5 on OBD2 port dropped signal voltage down to appropriate 5v. The issue i found, however, was a section of wire harness attached to firewall above air cleaner box. The wire harness was stretched tight (from factory). Plenty of slack over by brake booster BUT the harness was rubbing on lid of air cleaner. I detached harness from firewall, stripped cover off and found one of the grounds was worn thru along with 3 other wires. I repaired the wires and tested voltages again. I am now getting 5v for signal reference wires without scanner plugged in and "NoBus" is gone and guages are functioning! I haven't started and ran it yet because everything is still pulled apart. Will report back once everything is buttoned up. Thanks for all your help. Oh! Original PCM shows it's working while rebuilt PCM still says NoBus. I'll see what's up with that once it's put back together.

 

Awesome.

Yeah, replacement PCM's are a real crapshoot...... NONE of the 'refurbisher' companies have a much of a good reputation...... Been that way forever though.

 

unfortunately, we're over a barrel on that one. Quick update: got it all buttoned up(had to do untake gaskets at the same time), about finished up rebuilding the transmission soon. Will give an update once it's all put back together.