PCM / BCM / wiring issues? P1686 P1687 and instrument cluster haywire - JeepForum.com
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post #1 of 41 Old 06-26-2020, 08:43 AM Thread Starter
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PCM / BCM / wiring issues? P1686 P1687 and instrument cluster haywire

The TL;DR version:

  • Started happening about a year ago.
  • The car starts and runs/drives fine; no apparent problem with SKIM or the keys. The various engine sensors all correctly report data via ODBII port (coolant temp, oil pressure, speed, etc.).
  • Instrument cluster, door window/lock switches and overhead console are normal with key in accessory position.
  • Instrument cluster goes haywire about 0.5 seconds after engine start and door power window controls intermittently stop working. Overhead console shuts off entirely. Interior dome lights sometimes frozen "on".
  • "Haywire" = needle gauges drop to zero, airbag, ABS, CEL, SKIM, etc., lamps come on and off, random chimes.
  • Disconnecting the battery for a while, or performing the DRBIII PCM clear / battery disconnect sometimes brings the gauges back for "a while" (sometimes last for days, sometimes immediately back to bollocksed).

The longer version:

When the symptoms are present, DRBIII reports the same DTCs for engine and transmission (surprised to see these in the transmission section):

P1686 - No SKIM bus message
P1687 - No cluster bus message

While replacing entire cooling system, all oil sealing gaskets/seals, I didn't spot any damage to any engine bay wiring (despite evidence of critters making their home on top of the intake manifold / valve cover and under the driver's side headlight for a time). I've also pulled off / cleaned a handful of the small ground eyelets around the engine bay (as recommended by Uniblurb). I've pulled the driver's side door wiring out and that seems fine, too.

WHEN the instrument cluster is working, the airbag fault indicator always illuminates with a chime after engine start (and remains illuminated). I replaced the clockspring with a non-OE version (Dorman?) about two years ago to resolve this fault, but it seems to have returned.

I've also had intermittent shorts (with visible burn marks) in the left rear tail light housing over the years (resolved / broken / resolved / broken / resolved by bending and sanding the light bulb contacts, ad infinitum). I have a knock-off tail light housing that I'll probably throw on there (although the factory housing seems fine now).

P1686 / P1687 seem to be a rather common problem with WJs (and XJs, and even much newer, completely unrelated Chrysler products!), but each version of the problem is nearly unique in the solution (which is troubling).

When this whole thing is going haywire, the DRBIII seems to have intermittent trouble accessing the BCM, overhead console module, door lock modules, etc. It's as if they disappear?

The DRBIII tool is never able to communicate with the airbag module, regardless of whether things appear to be "fine" or not; it always comes back with "NO RESPONSE FROM ORC" (or "NO RESPONSE FROM SRM" for the airbag switch). Don't know if this is simply because the DRBIII airbag diagnostic section is for different Chrysler vehicles?

I'd also add that the DRBIII tool is never able to talk to the instrument cluster, either, reporting "NO RESPONSE FROM MIC".

I have some small suspicion the "new" airbag clockspring (as recent repair) might be causing this, but reluctant to buy another clockspring - if a clockspring goes bad, could it cause weird electrical problems elsewhere?

I'll probably remove and inspect the PCM as another "next step", but figured I'd start a thread here to solicit ideas from y'all.

Thanks!


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post #2 of 41 Old 06-26-2020, 09:30 PM
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If your WJ has a sunroof, the passenger side drain tube can crack and leak into a couple of big white connectors behind the passenger side kick panel and cause all kinds of electrical gremlins including no bus. Or, maybe it was one of the power window modules going bad and causing the data bus to go down? Maybe research those issues and see if the symptoms sound familiar. Good luck, you'll figure it out.
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post #3 of 41 Old 06-27-2020, 09:52 AM Thread Starter
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Quote:
Originally Posted by Rixdafix View Post
If your WJ has a sunroof, the passenger side drain tube can crack and leak into a couple of big white connectors behind the passenger side kick panel and cause all kinds of electrical gremlins including no bus. Or, maybe it was one of the power window modules going bad and causing the data bus to go down? Maybe research those issues and see if the symptoms sound familiar. Good luck, you'll figure it out.
No sunroof, but the passenger side door seal is damaged (and probably leaks slightly) from having to coat-hanger into the car a few years back... I'll add pulling the passenger side door panel, kick panel, etc., off to my list of things to check, thanks!

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post #4 of 41 Old 06-29-2020, 03:01 PM Thread Starter
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I pulled the PCM out, and the various wiring harnesses in the vicinity all look fine; no damaged insulation or wiring breaks.

My WJ is equipped with the diagnostic junction port at the steering column, but I'm still trying to educate myself on what I should be looking for (certain resistance values for pin X to ground, or find an oscilloscope).

After putting the PCM back in, there are no DTCs after a few stops/starts, and the MIC / instrument cluster seems to operate normally again (other than a persistent airbag CEL). The MIC, BCM and airbag module are still invisible to the DRBIII. Driver's side and passenger's side door modules are accessible.

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post #5 of 41 Old 07-02-2020, 10:06 AM
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I'll throw this out there. I had the same issues with gauges going to zero, all dash lights on, power windows inoperable, only drives door lock worked, the overhead console had lines only. Sunroof worked as did the radio. This would happen 5 or 20 minutes into the drive. I could stop and turn the Jeep off and it would reset but, the time interval to failure would me seconds or minutes.
After living with this for about a year, I noticed the ABS light would come on a fraction of a second before everything went nuts so I figured I would start there. Pulled the console and cleaned/scraped the two ground terminals around the ABS module and used contact cleaner on the ABS plug.
Its been 5 days now without a failure. But, as you said, this may reoccur in a few more days. If it does I'll repost here.
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post #6 of 41 Old 07-02-2020, 04:31 PM Thread Starter
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PCM vs. oscilloscope

The ABS module has been intermittently acting up (when everything else is "fine"), but seems to be correlated with not haven driven the vehicle in a while. I'll go track down where the ABS module lives and see if I can do the same thing (just to rule it out).

My PicoScope 2204A arrived today and I had a chance to look at things on the diagnostic junction port.

First picture is key off, a steady 160mV DC.

Second picture is key in accessory, ~ 9V DC.

Third picture is with engine running, looks like spikes to 12V DC, and just tons of noise. Alternator? I haven't popped the PCM open, but the exterior of the case looks to be in excellent shape.

I'll do a second post for the BCM, which also looks a bit odd between key off, key accessory and engine running.
Attached Thumbnails
PCM-key-off_05.jpg   PCM-key-acc_12.jpg   PCM-key-on_31.jpg  

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post #7 of 41 Old 07-02-2020, 04:35 PM Thread Starter
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BCM vs. oscilloscope

First picture is BCM, key off (driver door open, interior lights on).

Second picture is BCM, key accessory.

Third picture is BCM, engine running.

Second and third picture look like it's doing the same thing.

Peak voltage looks consistent across all three.
Attached Thumbnails
BCM-key-off_12.jpg   BCM-key-acc_05.jpg   BCM-key-on_16.jpg  

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post #8 of 41 Old 07-02-2020, 08:59 PM Thread Starter
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The PCM noise only while the engine is running had me try unplugging the alternator... it SEEMS to have cured the problem, but I'm going to wait until I can rebuild/replace the alternator to call that the fix.

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post #9 of 41 Old 07-06-2020, 04:49 AM
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Hi @AustinLonghorn , do you have any news about?
A friend of us is having a really similar issue, and casually everything started after the alternator change...; he changed again the alternator and checked the new one, everything was ok, but the issue is still present...

Also the @Montreal300 fix is really interesting, I wonder if he hasn't had it yet after the intervention on ABS plug

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post #10 of 41 Old 07-06-2020, 08:07 AM
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Quote:
Originally Posted by mak_v8 View Post
Hi @AustinLonghorn , do you have any news about?
A friend of us is having a really similar issue, and casually everything started after the alternator change...; he changed again the alternator and checked the new one, everything was ok, but the issue is still present...

Also the @Montreal300 fix is really interesting, I wonder if he hasn't had it yet after the intervention on ABS plug
Well over a week now without any problems.
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post #11 of 41 Old 07-06-2020, 01:22 PM Thread Starter
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Quote:
Originally Posted by mak_v8 View Post
Hi @AustinLonghorn , do you have any news about?
A friend of us is having a really similar issue, and casually everything started after the alternator change...; he changed again the alternator and checked the new one, everything was ok, but the issue is still present...
mak_v8 - I dropped off the alternator this morning at a repair shop and am still waiting to hear back from them. I'll definitely update this thread when I get a repaired or new alternator back in the car.

I also sheared the head off the M10-1.5 65mm alternator mounting bolt, so I have to get the old bolt out of the alternator bracket now, too... argh! You try to fix one thing, and another thing goes wrong...
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post #12 of 41 Old 07-06-2020, 06:44 PM Thread Starter
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My alternator (Bosch 6 004 ML0 001, original with Chrysler stamp) tested fine at the alternator repair place. The battery also tested fine.

So now I'm at a loss: with the engine running, the ECUs can seemingly only talk to each other if the alternator positive lead is disconnected.

mak_v8 - have you tried the same trick? Disconnect negative terminal on the battery, disconnect the alternator positive lead and safely cover it / prevent it from touching ground, reconnect the battery and run the engine briefly on just the battery to see if ECUs stop misbehaving?

I have a new problem now in that my alternator bracket is ruined; will have to visit a scrap yard this week to find another bracket before I can continue to debug the PCM / PCI bus issues.

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post #13 of 41 Old 07-07-2020, 05:02 PM
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@AustinLonghorn ,
the WJ with the issue is not my WJ, but the WJ of a friend of mine.
He changed two times the alternator, but the trick to run with the alternator disconnected I think that was not tried.
His issue was (and I am saying "was" because the WJ has been sold today... :sad:) pretty much similar to the Montreal300 issue, crazy dash, EVIC not working, windows not working, etc; and after a normal off-on the engine everything became "normal", ...till the next time.

I am interested in finding the solution and the culprit of this issue, my friend was fighting this battle for a long time, selling the WJ has been like giving up.

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post #14 of 41 Old 07-08-2020, 09:21 AM Thread Starter
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Quote:
Originally Posted by mak_v8 View Post
@AustinLonghorn ,
the WJ with the issue is not my WJ, but the WJ of a friend of mine.
He changed two times the alternator, but the trick to run with the alternator disconnected I think that was not tried.
His issue was (and I am saying "was" because the WJ has been sold today... :sad:) pretty much similar to the Montreal300 issue, crazy dash, EVIC not working, windows not working, etc; and after a normal off-on the engine everything became "normal", ...till the next time.

I am interested in finding the solution and the culprit of this issue, my friend was fighting this battle for a long time, selling the WJ has been like giving up.
Ahhh, that is unfortunate, sorry to hear!

I've spent too much time/money repairing a slew of other things recently to give up, hah!

https://www.jeepforum.com/forum/f310...prits-4399975/

I picked up two alternator brackets, another OE Bosch alternator and a 2004 WJ 4.0 Limited PCM yesterday at a salvage yard; I'm going to try a cheapo new alternator first (Power Select 13777N), then maybe see if I can manipulate the salvage '04 PCM with DRBIII on a tabletop.

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post #15 of 41 Old 07-09-2020, 07:19 PM Thread Starter
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So the cheapo Power Select 13777N doesn't fit properly on either alternator bracket I have; it's probably 1mm too narrow on the bottom 'channel' area. Have to send it back to Rock Auto.

For grins, I threw the $20 salvage yard Bosch alternator on the car instead... and surprise, surprise, things seem fine now. The bus also looks normal, too (pin 1 on the diagnostic junction port).

I'm still not able to access the MIC or ORC via the DRBIII tool which is odd ("NO RESPONSE FROM MIC", "NO RESPONSE FROM ORC"), and I still have a persistent airbag warning on the instrument cluster.

I'm hesitant to call 'replacing the alternator' the fix just yet, but I'll go drive it around for a bit tomorrow and see how it behaves!
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