PCM?? Dead gauges and SKIM - JeepForum.com
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post #1 of 41 Old 09-13-2018, 06:04 PM Thread Starter
kdubbs46
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PCM?? Dead gauges and SKIM

Ok,
2001 WJ, 189,000

About a month ago, was driving to work and all the gauges went dead. Jeep still ran, no issues getting the last 5 miles there. Worked to lunch, and went outside to check codes. P1687, and no problem starting (MIL light on). End of day drove home, no problems. MIL light goes off some days after.

Fast forward a month and on the way home from work all gauges dead again, flicker once back to normal, then dead again. Got her home. 4 hours later i go to leave (assuming that i'll be ok) She starts strong, 3 seconds later she cuts out (SKIM light came on/off/on again, still no gauges) . Actually, the volts creep up a hair as does the oil pressure...barely.
I removed, brushed and sprayed the motor ground, the large ground wire next to the in-engine fuse box, and the small one on the drivers side quarter panel as well. , I've check the door wiring (no visible issues). I've checked all PCM and BUS related fuses. I've pulled and sprayed the PCM plugs. Ran the instrument cluster check, all good. I've left the battery (1.5 years old) unplugged for a day...Still nothing.

I replaced the main harness (non OEM) and the CPS (OEM the second time ) about a year ago, also.

This time and the last time this happened was after a significant rain and a humid and misty day. The air has yet to fully clear so i'm hoping for some dry air and a miracle.
My signs point to bad PCM, but I know Jeeps like solid grounds and good batteries.
Any help would be greatly appreciated.

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post #2 of 41 Old 09-13-2018, 06:53 PM
blueseasons
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Codes?
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post #3 of 41 Old 09-13-2018, 08:03 PM
KC0GFG
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I am chasing the same gremlin, I replaced the PCM and was good to go for about a day, i'm on my third PCM each presents different issues so i'm going to try a different company.

in addition to the pcm I've replaced cam and crank position sensors, still dies intermittently

PM if you want to know who ive been having bad luck with
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post #4 of 41 Old 09-13-2018, 08:06 PM
KC0GFG
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oh its a 2000 wj i've been chasing the gremlin on
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post #5 of 41 Old 09-14-2018, 03:45 AM
GhostJeepWJ
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Yea without knowing the codes it's throwing, my best guess is PCM. The problem with them is actually getting a good one. Either from a PnP or from a 3rd party vendor. Usually takes most a few tries before getting one thats good.
Give @OldWJs a message he may be able to help you out.
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post #6 of 41 Old 09-14-2018, 04:10 AM Thread Starter
kdubbs46
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Quote:
Originally Posted by blueseasons View Post
Codes?
Just 1687...and only the first time. Now I check for codes and nothing. Not even "done"
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post #7 of 41 Old 09-14-2018, 06:07 PM
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Here's one place I'm going to say its NOT the PCM, provided I'm understanding correctly that it 100% reliably starts every single time, and then shuts down.

You likely have a problem in the PCI bus wiring somewhere in the vehicle. There are as many as 15 electronic control modules in these Jeeps and the PCI wire runs between all of them and is what is used to communicate between them. The PCM, gauge cluster and SKIM are all modules on this bus. The handshake between the SKIM and the PCM only happens when you start the vehicle. After a successful handshake you could pull the SKIM off (or lose PCI bus connectivity) and the vehicle will continue to run, until you try to restart it. But loss of bus will cause loss of gauges, all the info on the gauges is sent over the bus from the PCM. This explains why when you lost bus when you were driving, you continued on your way, but now that you have no bus when you're trying to start it, it shuts down immediately.

Believe it or not the best place to start is by looking at the wiring running from the body to the driver door in the little rubber boot. That and the connector often causes problems. The PCI bus runs out to the driver door because that module with the window and door lock controls is actually another electronic control module. Try completely unplugging that connector and seeing if it helps.

I can tell you my first experience with this was starting my first WJ to go to work one morning, and it shut off right away. A couple of times. I noticed the gauges were doing really whacky things. What I also noticed was a kind of static sound coming from the speaker in the driver's door so I focused my attention there. When I pulled the connector apart for the wiring to the door (at the body) a bunch of rusty water ran out. Some WD-40 to dry it and I put it back together, and the Jeep started and ran. What happened was that the water conducted enough of the electricity away from the PCI line to ground that it caused all of the modules in the vehicle to be unable to communicate with each other. And the electrical pulses on the PCI bus that are used to transmit the data was causing the speaker to make noise since the speaker wiring goes through that same connector. I thought my experience was unique until I started reading on here about all the other people who've had trouble in that area.
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post #8 of 41 Old 09-14-2018, 06:08 PM
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Quote:
Originally Posted by kdubbs46 View Post
Just 1687...and only the first time. Now I check for codes and nothing. Not even "done"

Yes, because the instrument cluster can't communicate with the PCM to get the codes.
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post #9 of 41 Old 09-15-2018, 12:13 PM
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My 2000 is doing the same. Replaced pcm still doing it. There is a distant clicking noise coming from the drivers window controls. Windows won't work a.c. is in and out and the gauges go crazy. If I cut it off and click to ac on the ignition the Windows work but not while running. If I take the battery cables loose and tie them together for a few hours I'm good for about half a day. Overhead info center will come on but has no digits for any info(mpg,mte) I bought a used known good bcm but have not tried it yet. Any help would be gratefully appreciated.
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post #10 of 41 Old 09-16-2018, 07:40 AM Thread Starter
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OK...
@OldWJs Thanks for joining!! @Bryanp3344 I looks as though you have a similar grounding issue...Mind starting your own thread?...i'll gladly help you if i can.

Starting at the beginning, you are correct. She starts very strong every time, then goes off after 3 seconds. The SKIM light goes on, off then back on solid.
I pulled the drivers door plug completely and tested again. Same result.

Two strange things though. First, there was a significant amount of moisture in the boot and on the plug itself. As you said, I sprayed the plug (with a LOT of electronics cleaner, should i have used WD?), replugged, and still same result. Second, upon inspection of the wiring leading to and from the plug, I noticed that the 2 green wires (on both sides of the plug) were taped together hastily. I didn't have the time to pull them apart and do it properly, but it seemed as though they were stripped and merged together. Weird because I am the first "owner" of the vehicle (bought off-lease) and have never had any work done on her that wasn't with my own hands. Sprayed that liberally too.

Anyway, as I was praying for (and somewhat expected) when the weather dried out yesterday I went out to give her another chance. Turned to on, gauges on, SKIM light on then off and stayed off. Started and ran perfectly!

So, unless its possible to test it somewhere (which from my forum searching looks to require an oscilloscope) it seems as though my next course of action should be to locate all PCI bus connections, spray them, maybe some dielectric grease as well, close them up, and wait for the next wet humid day. Sound right?
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post #11 of 41 Old 09-16-2018, 07:17 PM
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I have a 2004 jeep grand cherokee 4.7 ho and this past month ive had an electrical nightmare. I was having a problem where i would start it then the anti theft light would come on and it would stall after 2-3 seconds. I got a new PCM, and that problem is fixed, but now the anti theft light still turns on about a minute or two after starting and sometimes it stalls right when that light comes on, other times the light comes on and it still runs fine. A few days ago the gauges stopped working when i was driving, so i disconnected the battery and cleaned the terminals. That fixed it for a day but now, every once in a while it still stalls after a few seconds, but not usually. I’m getting a new sentry key immobilizer module in hopes of fixing the problem with the anti theft light still coming on a minute or two after starting and sometimes stalling, but i have no idea about the guages not working. It’s throwing out random codes, but it has a new pcm and the connections are all good. Tonight, the windows have stopped working, the interior lights dont come on, and the guages still dont work and now instead of the check engine and anti theft light, the air bag and abs are on when turned on. I am hoping the SKIM im getting will help once i program it to the key, but i have no idea. Maybe the crankshaft position sensor or the BCM?? Any thoughts?
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post #12 of 41 Old 09-17-2018, 12:49 AM
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Ok here we go….
The P1687 code is for “NO BUS”. This code is given when the signals over the PCI BUS LINK is not received as needed by other modules. This link is used by ALL of the computers to talk to each other. Since the instrument cluster is intermittent and the jeep still runs, it’s not the cluster with the problem. Same goes for the SKIM. The SKIM in default mode sends out a NO RUN signal, since the Jeep does run with the SKIM light on, it’s not the SKIM MODULE. You AC compressor is probable having issues also, turn on/off or not turning on, then minutes later, turns on.
All of these things share on link, the PCI BUS. The PCM sends out the signals over this link to talk to the others, the problem is a bad signal send to the other modules from the PCM…… replace the PCM.
I had the same issues with mine, and the PCM fixed it.
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post #13 of 41 Old 09-17-2018, 08:52 AM
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Just an FYI for those replacing a PCM, just cause you get a reman'd (cause it's not new, Mopar stopped making them a long time ago) doesn't mean that it's reman'd correctly. In alot of cases, it takes multiple attempts to get a good one. Sometimes on the first shot, sometimes maybe 2 or 3 before you get a good one.
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post #14 of 41 Old 09-17-2018, 10:24 AM
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GhostJeep WJ is correct on the PCM thing. Buy the PCM locally, so when there is an issue with it you can walk into the store and exchange it without shipping charges.
I get mine from the local NAPA store, they are repaired by A-1 Cardone (2 year warranty) and I order it pre-programmed with the mileage and VIN from my WJ, so when it arrives i just plug it in and go.
The difference in prices is whether the unit was rebuilt or re-manufactured.

NOTE: Keep in mind, there are 2 types of repairs, rebuilt and re-manufactured. Rebuilt has had ONLY the bad components replaced on the circuit board and re-manufactured has had ALL the components replaced on the circuit board. So on a rebuilt, it the PCM is 20 years old, so are most of the electronics.
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post #15 of 41 Old 09-18-2018, 05:49 AM Thread Starter
kdubbs46
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Ok....
I'm failing to see how this is a bad PCM if this only happens after an extended rain and humidity.
Now that it is somewhat dry out the Jeep is working perfectly. (see post 10)

From what I've read this seems like there is a short happening somewhere in the PCI bus spiderweb. Where, besides the driver door (which, due to the moisture found, is still suspect I think), should i be looking. Anyone know where I can find the locations of the 15 +/- modules that the PCI bus connects to?

Big thanks to all of you chiming in on this.
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