@sab Thank you for tagging me here. My NO BUS issue has not come back. Although I'm still battling other wiring issues (no dash or instrument lights work, airbag light is on, horn issue, etc).
@The Flying Scot I bought a wrecked 1999 TJ. The frame was shot, so I sourced another 97-02 frame. Bought a 2002 tub. And then put the frame, tub and many of the parts from my wrecked TJ together. This caused many issues as they didn't leave the factory together, and I was sourcing lots of used parts that were questionable. The biggest issue I had was the NO BUS issue. I looked all over the place and tried many of the fixes I saw on here and on other sites/videos to fix it. Nothing worked. I eventually sent my PCM to Mark at Wrangler Fix and they determined it was fine and not the problem. I took the instrument cluster out, cleaned the wiring harnesses to the back of the cluster, bent some of the wiring prongs, etc. NOTHING worked. Sab helped me read the wiring diagrams from the FSM (by the way, those are a God send, read them!). We traced the wires that were the likely culprit, and they are as he mentioned above: C28 and C30 in the gray connector going into the PCM. Because this Jeep was never going to be a show vehicle, and it's a second or "beater" vehicle for me, I took the easy way and ran all new wires. I didn't care what it looked like. I just needed working gauges. I picked up 20 gauge twisted wires from Home Depot, cut C28 and C30 just after the C3 wire connector at the PCM, and ran them temporarily through the passenger window and across the interior to the back of the instrument cluster, where I cut the same wires at the back of the cluster (essentially bypassing the entire wire path in the loom). This is what fixed mine. The NO BUS issue went away and all my gauges worked. So I ran the wire permanently and tied in into the regular loom, ran it through the firewall, and it has been fine since.
However, I will warn that this is a pretty drastic repair, and the reason it fixed mine is I believe a wire inside the main wiring loom that feeds into the dash is broken and/or grounding from time to time (the NO BUS issue came and went for a while before becoming permanent). From what I can tell, most people were able to fix their issue by cleaning the connectors or bending the pins on the back on the instrument cluster. I tried that 5+ times and it wasn't my solution. What is still confusing me is that my data link port worked when the gauges didn't and when I was getting the NO BUS issue. And if you read Sab's screen snip above of the FSM, that is on the same wiring path (the only thing on the wiring path besides the gauge cluster), and SHOULD NOT have worked if these wires were broken. I know it worked because I used a code reader that can read instant data to determine what was going wrong with a throttle issue I had, and it could read all my codes just fine. That led me to believe my gauge cluster was bad since I clearly had a signal all the way to the data link port, and not to the gauges. I tried another gauge cluster from my local pick n pull, and it had the same NO BUS issue. To this day I still don't know why the data link port worked when the gauges didn't. All I know is that by running new wires from the PCM to the instrument cluster, I have working gauges now. To me that was easier and more worth my time than it would have been to take apart the entire wiring harness and look for a broken wire.
But now I have a horn that when I have the relay plugged in, the horn will randomly start blowing on it's own and stays on steadily until I pull the relay. So I either have to pull the wiring harness apart, or do the same thing I did with the gauges wire and run a new wire. I suspect it is also grounding out somewhere.
I don't know if this is the solution you want or needed, but it is what worked for me. If you try all of the usual fixes and they still don't work, you may have to do something as drastic as me. However, I would encourage you to start with checking out Wrangler Fix. You can send your PCM to them and they will test it out on their Jeeps. If it's bad, they put the cost of the diagnostic towards the cost of a replacement PCM. If it's not the problem, they package it up and send it back. It's a low cost for the peace of mind to rule it out of the equation. Between that, trying the connector cleaning and prong bending steps on the back of the instrument cluster, it will give you a start on diagnosing it. If your data link port stopped working, as you mentioned, it may be as bad as mine and require new wires to be run (in all honestly it was quite simple and took me maybe an hour) or locate the broken wire and fix it. For me, running new wires was much faster and easier.
It will also help if you can let us know what you mean when you say it wouldn't start. Was it cranking and never fired up? Would it do nothing at all when you turn the key? TJs were known to have faulty ignition switches in them, and many of us have dealt with them. I replaced mine, and even now at random times when I go to start mine it will not even attempt to turn over. I have the move the key around in the ignition, wiggle it back and forth in different ways and try again, and then it fires right up. It really delayed me getting my Jeep fired up for the first time as I had a wiring/ground issue, NO BUS issue, AND an ignition switch issue that I didn't know about. You could be in the same boat where you have a couple different issues that make diagnosing one at a time confusing, as you're trying to take the entire problem as one.
