No bus issue: what haven't I tried yet?

[Gormy]

Hey all,

First, big thanks to this community for all the help you have provided so far. For those that haven't seen my previous posts, I bought a wrecked TJ and essentially built a new one from scratch using the drivetrain/interior/wiring/some body parts from one, frame from another, tub from another, axles from another, and so on. I'm down to the last couple issues to fix, but the Jeep runs and drives amazing.

The biggest issue I'm chasing is the No Bus issue that we all hate dealing with. The issue started right away after assembling the "new" Jeep. It went away a few times and all my gauges worked when I drove. Was working kind of consistently. Then one day they stopped and haven't come back. The only thing that happens right now is the oil pressure gauge climbs ever so slightly when I turn the key on. Nothing else works. I have tried many fixes so far, as I will list below:

- Started simple with cleaning the connections at the instrument cluster. Bent the pins a little bit to promote a better connection. Dielectric grease. No luck.
- Tested the continuity of the twisted pair of wires that feed from the PCM to the cluster (can't recall the colors, I think a violet wire and a white/black). They have continuity.
- Tested for ground at the two ground wires at the PCM (A31 and A32 in the black connector). I have continuity and no resistance.
- Tested for 5v (with key on) coming from A17 in the black connector and B31 in the white connector. I have readings of 5.17v and 5.21v respectively.
- Tested for 12v power at A2 and A22 in the black connectors at the PCM. I have 12+ volts at each.

I don't think the 5v sensors would be an issue because I don't have a no start issue in combination with the No Bus, but I was already digging in there so why not?

So from what I'm understanding, I have power to the PCM, proper grounds at the PCM, unbroken wiring to the instrument cluster, and what should be clean connections at the cluster (this could still be an issue. From what I've seen, this is often the problem, but I have done all I can to clean that up).

Where do I go from here? Is it likely the PCM is sending a bad signal to the instrument cluster? Is the cluster receiving a good signal (as evidenced by the oil pressure gauge moving a little bit) but isn't always functioning correctly? Both of these are expensive fixes, and I don't want to take guesses and spend money I don't need to.

Thanks y'all!

 

[macleanflood]

Year mismatches causing issues perhaps?

-Mac

 

[hear]

I feel like I just had this same conversation in another thread, but I chased this forever on an XJ, which has much of the same wiring in this area. Anyway I never did resolve it, but we did discover that some readers worked no problem, but others wouldn't work. IDK what would cause that sort of behavior, but it's what we saw. FWIW, my OBDLink CX was one that could communicate when nothing else we had would. ¯\_(ツ)_/¯

 

[HaydukeLives!]

I'm sure some have read my issue before but my gauge needles will drop sometimes and "NO BUS" appears in the odometer reading....and sometimes.....I can honk my horn once or twice and the gauges all come back on and the NO BUS goes away. I've cleaned and dielectric greased everything in the instrument cluster area. There are still some areas I need to investigate though. Good luck.

 

[macleanflood]

I can honk my horn once or twice and the gauges all come back on and the NO BUS goes away.

I do recall some folks having issues with their CPS and they finally traced it to a bad clock spring shorting the 5v sensor circuit to ground...

Perhaps you're on to something here and it's the clockspring behaving badly?

-Mac

 

[Gormy]

Hey all. Just getting back to this now. The Jeep has been parked for a while as it wasn't running right. I pulled the PCM and sent it to Mark at Wranglerfix, just to rule that out as an issue. Everything checked out fine. After putting it back in, I chased the issue with it running poorly. That was a bad throttle position sensor. That has been fixed and it is running great again, but still have the NO BUS issue. However, the OBDII port works fine as I am able to read and clear the codes (cleared the one for the bad TPS).

So to add to my list of steps taken above, I can rule out the PCM being an issue. I also went to to local pick-n-pull today and grabbed an instrument cluster out of a 1999 Wrangler. Brought that home and put it in. No change, it still has NO BUS reading. All the same issues exist. So I am going to rule out a bad cluster. I took both grounds off near the instrument cluster (one near the kick panel in the footwell and the one on the speaker mount. I wiggled them around, adjusted, put them back on, and still NO BUS.

So what else is there? Between my original post and this update, I feel like I've ruled out everything I've seen listed online. I have an airbag light and no horn, so I'm guessing the clock spring is bad. But from reading the wiring diagram in the FSM, that is not something that will cause this issue. Everything else on the Jeep works as it should. I have no wiring issues anywhere. It runs great. All lights work. Radio works. What else is there to try? This is the last thing I need to do to make it a daily driver. I don't like having no gauges as I drive.

 

[Gormy]

This is finally resolved!

It ended up being a broken wire somewhere in the loom between the PCM and gauges. I don't know exactly where, and I don't care at this point. I just wanted a working instrument cluster. What threw me off is that the data link connector (OBDII port) worked fine, and that is on the same wiring path (the only other thing on the same path) as the cluster. Why that works perfectly and the gauges don't is beyond me. The only thing I can think of is a broken wire between the two, which allows the data link connector to still read. I worked with Sab on here to come up with some tests, and he recommended that I run a temporary wire from the PCM to the gauges, and that worked perfectly. So I ended up cutting the wires at both the PCM and gauges, running a new pair in the loom and in through the firewall, and it is now the permanent wire for this. Is it pretty? Nope. Does it work? Hell yes.

Thank you all for your tips!

 

[midville1]

This is finally resolved!

It ended up being a broken wire somewhere in the loom between the PCM and gauges. I don't know exactly where, and I don't care at this point. I just wanted a working instrument cluster. What threw me off is that the data link connector (OBDII port) worked fine, and that is on the same wiring path (the only other thing on the same path) as the cluster. Why that works perfectly and the gauges don't is beyond me. The only thing I can think of is a broken wire between the two, which allows the data link connector to still read. I worked with Sab on here to come up with some tests, and he recommended that I run a temporary wire from the PCM to the gauges, and that worked perfectly. So I ended up cutting the wires at both the PCM and gauges, running a new pair in the loom and in through the firewall, and it is now the permanent wire for this. Is it pretty? Nope. Does it work? Hell yes.

Thank you all for your tips!

Sir, could you please reach out to me? I'm having an issue with my gauges not working. The test works and I've checked and moved all the grounds. Sometimes I'll get a reading from a gauge, but then it will cut out a second later. I feel I might have a broken wire somewhere and I would like to try your diagnosis if you could shed light on which wires you jumped out. Thank you for any and all help. [email protected]