So here goes, I just bought a 2002 1500 Van with a 5.9l, low miles. I do all of the regular stuff, oil change, check the brakes etc., no issues. I decide to install a back up camera and park distance sensors. Got it all working, no issues, but the I noticed that the PO had installed an electric fan as a pusher, in front of the A/C condenser. It is TX, so probably need the extra boost for the summer. Anyway, his wiring didn't look the greatest, and he did not have it fused, but I figured I would leave it to another day. Dumb!. Hooked up the battery, massive arc from the aux fan relay. Now the fun begins. Re-wired the fan correctly, fused it etc. Try to start the van, the dreaded no bus on the odometer. Figured I blew the PCM, but did all of the usual sensor checks, all a-ok. No blown fuses or relays. Still the no-bus. Unhooked the PDC, snapped everything back in place, and the van starts like nothing every happened. Tried it 2-3 more times, no issues. Great, now I have an intermittent problem, (but a good PCM, so it could be worse). That was 2 days ago. Go out today, and the no-bus is back. So I pull the connector on the PCM to check my grounds and 12VDC. Grounds are good, Pin 2 has volts, Pin 22 nothing. I disconnect the battery completely, cause I figure I'll run a continuity test on the 22 pin back to the PDC, thinking I'll find an open. Nope, I've got about 1 ohm of resistance. I hook up the battery, cause my diagram says 22 is always hot, no voltage. Check for 12vdc across the fuse, and it is there. Pull the battery again, check for a short between 22 and everything else in the connector, no shorts. Checked for a short between 22 and ground, wide open.

So I'm more than a little confused, and any help, guidance or suggestions would be greatly appreciated.

 

The No Bus message indicates a loss of communication between the digital odometer and the PCM. The problem could be in the instrument cluster if you're sure the PCM is good. BTW, how did you determine the PCM is good?

 

I got the no buss after a short. After messing with the wiring harness and PDC, the truck started multiple times, no probs. After sitting a day or two, I'm back to the same issue. It looks like the pin 22 wire to the PCM doesn't have voltage but tests good with an ohm meter for continuity.

 

Well I have an update, but no fix as of yet. Went through the wiring harness as best as I can without a full wiring diagram, (one is on order should be here mid-week). Anyway, took the PDC apart, replaced all of the relays and checked and reseated all of the fuses. I now have 12vdc on Pin 22, don't ask me how or why, cause all of the relays I replaced tested fine. Still no bus. Went back to the sensors, now I'm not getting 5vdc on any of them. Unplugged all of the sensors I could find at the engine, no joy. Checked the transmission connectors, the round one on top bare spots on all of the wires, trans fluid I'm guessing. sealed them all, checked for shorts through the center PDC connector, everything looks fine.

Is there anything else that could be holding down the 5 volts that I have not unplugged? Like I said in my first post, the truck started numerous times after fiddling with the wiring, (which lead me to believe a short or open), then no bus again. I wouldn't think the 5vdc circuitry in the PCM would work after the short, and then quit over time, but clearly I am missing something or I would have it fixed by now. Thoughts before I order a new PCM? Thanks.

 

If you invest in a service manual from mopar you will find the +5V DC buss originates in the instrument panel. The instrument panel on our 2001 van has some very poor quality connectors that can work loose and corrode.
I recommend you remove the instrument panel, generally clean the connectors up and clean with electronics contact cleaner.
A good cleanup is a good idea for all the poor quality automotive connectors when you begin to have electrical issues.
Good quality connectors use GOLD plated pins that really resist corrosion.
WARNING: These modern vehicle are constructed from cheap plastic that gets very brittle as it ages and you can cause more problems than you solve if you are not really careful.
MY rule is to always remember it starts out broken and you go from there.

 

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Here is the latest, though it really is back to square one. I got my service manual while I was out of town, and started going through the wiring diagrams for the instrument cluster and the PCM. Ran the self test for the cluster, everything looks good. On the 2002, the +5VDC source is the PCM, so checked it leaving the connecter, no joy. Pulled all of the plugs on the sensors, plugged them in 1 by 1. No change, still no bus in the odometer window. While I was firguing out what I was going to try next, I started fiddlin' around with the relays in the PDC. (I never pushed it back onto the mounting ears, so it flops around a bit). Anyway, I hear the relays throw, including the fuel pump. I jump in the truck and try to start it, forgetting I still had the IAC and TPS disconnected. Hooked those back up, the truck will start, but stalls right away. If I feather it I can almost keep it running. Scanned for codes, and I threw a P0123 TPS ckt A high. Re-seated the sensor connector, the code disappears, but the truck still won't stay running. I tried at least 7-8 or 8 times to see if the no bus would come back, it didn't. Decided to take a look at threads and see what other folks with a no start no code conditions had found. A few folks swear that a weak battery can cause this type of problem. At the risk of offending some, I was a little skeptical, but I was using jumper cables to a battery on the bench to work on the truck, so I figured that maybe it was worth a shot. I put in a fully charged battery back into the truck, and guess what, the no bus error is back. No matter how much I move the PDC around, reset the relays, etc., I can't get back to the no code / no run condition. I am open to additional suggestions, but my current plan is to strip back the wiring harness from the PDC and see if there is any luck there.

 

Glad to hear you got your service manual. Appears mopar did make mods in the 1998 - 2003 series of vans.
The standard generic code reader will generally only read codes that that also can turn on the check engine light. That's all I have and it sucks! There are many codes that mopar throws up that a official reader can display. If the engine does not run there are probably codes in the PCM that can be listed with the correct reader.

 

Just got the van fixed a couple of days ago, and I wanted to make sure it continued to work since the problem was intermittent. All sorts of joy, the fix works.

I got tired of chasing ghosts around the truck, mystery voltage drops, PCM signals that appeared and disappeared, including the 5vdc control from the PCM. Because the truck would start sometimes, but not consistently, I decided to send the PCM off to SIA Electronics in IL. $89.00 to test and verify good or bad, and that amount would be applied to a fixed unit if I needed it. They tested it the same day the got it, on the bench and in a test vehicle, no problems found. They sent it back and I got it 2 days later. Great folks.

Got out the wiring diagram, and started tracing 12vdc supply leads, since it seemed like every once in awhile moving the PDC would clear the issue, (never in a repeatable way).

For those with a service manual, 8W 10-6 the A0 circuit is electrically the same point, whether from the direct battery connection into the PDC or the circuit that feeds fuses 22, 1, 9, 17 or 19 in the PDC. What I found though was a huge voltage drop across 1, 9 & 17, (showing about 4vdc instead of 12+vdc. Since the PCM was still out of the truck, I put battery voltage right to the top of fuse 17, (the side closest to the front of the van, 10awg wire underneath). Just like magic, 12vdc everywhere just like it belongs, no blown fuses, everything looks perfect.

Now I disconnect the battery, but the PCM back in, connect all of the sensors, re-connect the battery. I have someone in the van to turn the key and see if the "no bus" returns. I put my jumper wire from the battery to fuse 17, they turn the key. The fuel pump & ASD relays latch, and the no bus doesn't come back. Turn off the key, remove my jumper, turn on the key, no bus returns along with the voltage drop. I do this about 5 or 6 more times, with the same result. Now I figure it is time to start looking at the wiring to see if I can find the weak link, to get to the point, I didn't but I have a work around.

I got a 10AWG fuse holder and a 20amp fuse, (equal to the rating of fuse 17). I connect an eyelet on 1 end and attach to the battery in on the PDC, the other end I attach a fork electrical connector which is the perfect size to replace the mini fuse. (A note, I did not have a side or 90 degree wire entry for the fork connector, which would make it fit a bit better than the wire straight in).

The fuse lid closes, the van has been running for days, and now I can go work on something else that is broken. Hope this helps someone else.