"No Bus" questions/help me save what's left of my hair!

01 4.0 AW4. "No bus" message pops up and never goes off. This is after spraying down my engine bay with water a few days ago. I unplugged the battery to avoid any issues like this.

I searched this forum and a thread I found said to unplug the CPS. I found the connection for the CPs on my truck, but it would be a royal PITA to unplug. Anyway, a MOPAR dealer mechanic told me yesterday I'd probably have extended turnover @ start, and rough idle, if CPS was going/gone. I am not having any performance issues whatsoever, so am inclined to believe my issue lies elsewhere.

My bus is still down though. I bought the replacement wires for the back of the dash yesterday (MOPAR PN 5016261AA) but it's only 1 of the 2 clips - this worries me in case it's the other clip that is the issue.

I need to know what other sensors might cause this problem. Again, it can't be O2, IAT, MAP, CPS, etc. cuz there's no effect on performance (not even a little). I was thinking speedo, oil pressure (though the guage hasn't worked for at least 6 months now - a dealer told me it's a bad guage so the sender still could be an issue), water temp, tach (comes off the CPS, no?), voltage, fuel guage. I don't know what other sensors there are that could be shorting out and bringing down the bus, much less if if even is a sensor shorting. I wouldn't think replacing the dash harness would affect anything since it could not have gotten wet when I cleaned the engine bay.

I know where the speedo, IAT and coolant temp sensors are. Where are the oil pressure and voltage sensors? What about the location of any other sensors that could be causing this?

1 other question I forgot to ask the MOPAR tech was if the ECU could be fully functional, but the bus between it and the dash not be. Is this possible, ie, could the computer need replacing even though it (basically) works? Or is it either functional or not, with no "in-between"?

Thanks guys!

With the battery disconnected, disconnect the wiring harness from the ECU and clean the connections. Do the same also to the main wiring connector at the firewall that powers all the instruments and warning lights in the dash. Some dielectric grease or contact spray in both areas should do the job.

The ADS relay in the main fuse box under the hood will casue it to flash No BUS. They are about 11 bucks too and none of the others match so you cannt swap it with another to see if its the problem. Get some WD-40 and spray all the connections around the computer under the hood. Yeah that damn wiring harness is hard to pull off and if there is corrosion on any of the pins then a no bus can happen. I learned the hard way when i tried to pull that harness apart. I had to replace 4 pins (male and female) on both sides of the harness. You talking a pain in the a$$. The connector on the ends of the harness when taken apart release the pins and you have to get a wiring sckmatic to repin the wires in the correct spot. And not all spots are used and the harness doesnt have a way to hold individual pins as you start replacing them back so its put all in at once or none. So be careful when pulling it apart. Hope you dont have this problem but it was mine and i got it done. But i work on electronics for a living( and i thought it was hard)

I already got everything apart once and back together - I'll find out in about 30 minutes if I broke any pins or not the first time through, I sure hope not, I seriously don't think so.

By dielectric - I asked my pops if he has some "dielectric grease" and he said, "ALL grease is dielectric!" Is this an accurate statement (I suspect not)?

Maybe I will try to replace the relay if nothing else works.

On a funny note: my AC compressor is going as well (or at least the clutch). I had a dream last night that my Jeep stalled, then wouldn't restart, and on my dash, where the CE light usually is, it said, "AC Compressor Clutch Malfunction" or something to that effect.....

True statement pretty much unless it is graphite based. I think the factory uses lithum grease to dip the tail light bulbs in, thick yellow stuff. I just keep a few of the large tubes of 'tune up grease' in convienent areas, tool box, work bench, etc, small tube under the back seat for on the road use.

When I wash my engine I do it at home, early in the morning, quick wet down with the garden hose on low, thumb over nozzle, then spray it down good with that citrus cleaner, go after it with a stuff parts cleaning brush and then hose it off again with low pressure tap water and repeat as necessary till it's all clean. I park it the nite before so that it's in the shade till about 9am and from then on it's in the sun till 3 or 4. I let the sun dry it out. Usually takes about 5 hours for the water puddles to evaporate out of the valleys in the intake manifold. Only then do I even put the key in the ignition. I do this once or twice a year and thats about it.

I'll make sure to use low pressure only next time, as opposed to a "pre-wash" cycle.

Ok so I disconnected all the sensors tonight, still same problem, so it's definately not CPS, any of the O2s, pretty much anything period. It's not the ECU - I plugged it into my brother's 99, and though it didn't run very well, it at least did not have the "no bus" message. Also, tried 1 or the other clip that plug into the dash, and then both together, and tried wiggling them, and still had the problem.

So what I'm left with now is actually believing a MOPAR service advisor, and replacing 1 of the dash wire harnesses. The part I purchased does NOT completely match colors of wires with either harness, though it certainly has more in common with the one on the right than the left - is this the clip I should replace? Should I have bought both clips, which is what I thought I was getting until I actually bought the damned thing and saw only the 1? Is is simply coincidence this happened right after I rinsed my motor down? There was absolutely no moisture in/behind the dash.

Suggestions?

EDIT: I went by AutoZone today just for shits and giggles to see what diagnostic codes came out of the ECU. They were:
1) EVAP - large leak ---> known issue
2) IAT unexpectedly high ---> new, probably related to the problem
3) Coolant temp unexpectedly high ---> ditto
4) turbo relief mechanism malfunction ---> funny as hell cuz I don't have a turbo!

Ok, so what does all this say? I removed *ALL* the sensors, including IAT and collant temp, to see if any of them were shorting out the bus........anybody know any good hair regeneration doctors?

Have you tried slapping the top of the dash, or pushing the gauge cluster? I remember on some 97+ XJs there was a TSB on the socket for teh gauge cluster.

BTW, Autozone likes to translate the codes wrong. Just get the code number (Pxxx) and do a search for it.

-Chris

Yeah, I tried that multiple times. I have all the code numbers - just outside in the rig, so I'll search for them later.

Before I search anything, I want to say how my guages worked fine last night. I was horsing around a little bit - including racing somebody well past 100MPH on the highway (stupid Acura - I had him toasted! by a Jeep! I wonder how he feels about that?) - and noticed, after I slowed down, that everything except my tach and speedo were working, but I still had a "no bus" message. Then I was horsing around some more, and EVERYTHING started working. I stopped at the store, turned her off, and when I came back out, everything was still working! I thought my gremlin was dead, until I started her up this morning.....and nothing again! Yay! I almost shit my pants today!

WTF is going on here? It obviously is a loose connection, but where??? Should I assume my speedo sensor is shot? It's been leaking synthetic ATF from the speedo housing for some time, but it's not like it's enough to even worry about keeping it filled more than once a year.......

Should I purchase a whole new wiring harness, and call it a day?

WTF why do the feds have all these stupid laws for newer vehicles......and this stupid liberal state.......dammit!!!!!!!!!!! What happened to good old carbs with no electronics? Don't we have mechnically-engaged 4WD because electronics are liable to fail!!!???

Possibility, when I was installing the fog light add on kit in my 98XJ I ran the single wire from the inside fog harness that I added thru that big cluster of wires under the master cylinder on the firewall. Used a very thin ice pick to make the hole. At any rate while I was down there I noticed a big block where the harness connects to the inside harness, above your left foot when you foot is against the kick panel. This big grey block had a bolt in the middle of it to hold it together, the bolt had backed all the way out and was so loose it was almost unplugging itself. It was a tight fit in there but using a whole bunch of 1/4 inch extensions I was finallly able to get a socket on that bolt and tighten it back up. I then checked the other one that was kind of under and down to the left of the radio. My symptoms were the dash dieing, loosing radio and presets. You might want to check that block out.

Just a couple of other questions I hope somebody can answer.

1) I know the speedo gets its info from the transfer case - where is the tach's signal originated from?
2) I've NEVER seen an FSM, so please excuse the stupidity - but does an FSM show/say, step-by-step, exactly what to check/do when trying to track down an electrical error (as I am here)?

krakhedd said:

Just a couple of other questions I hope somebody can answer.

1) I know the speedo gets its info from the transfer case - where is the tach's signal originated from?
2) I've NEVER seen an FSM, so please excuse the stupidity - but does an FSM show/say, step-by-step, exactly what to check/do when trying to track down an electrical error (as I am here)?

Click to expand...

Almost every wire that comes into the cab comes thru that connecting block down on the left side of the foot area.

I'll be sure to check that next, but I still don't know how water could have gotten into it. Stranger coincidences have happened to me than this issue starting as soon as I sprayed the motor down, though......the stupid guages came back up again earlier today, for example, and if they're out again when I go downstairs in a few minutes, I'll be sure to check that clip.