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Old 07-01-2011, 02:42 AM
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PCI Bus Issue

Hi,

I have a 2000 WJ V8 Grand Cherokee Ltd. It has suffered recently from the dreaded PCI bus issue with the usual gauges all dead, all trouble lights up, power windows not working etc. Have checked all connectors, wiring to doors, battery tested etc. All issues are cleared if you run the car with the alternator disconnected as soon as the alternator is reconnected issues immediately resurface. Have replaced the alternator but this hasn't solved the problem. PCI voltage is within normal range and I guess the modules are OK as these wouldn't suddenly repair thenselves in the abscene of the alternator similarly broken wires, condensation in loom or earth poor connections.

Any thoughts where to check next?
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Old 07-01-2011, 03:23 AM
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Re: PCI Bus Issue

I've been where you were and I understand your frustration, most of the search results has people having this problem, and no resolution.

I had it come up several times in slightly different forms for me..

Sometimes only the windows would stop, other times the gauges, and I think it caused a SKIM key problem. Other times the driver side door lock wouldn't lock any of the droors but it and the one behind it - most of the times that happens when the wires in the door jamb break, but mine were fine which meant a pci bus failure.

There were three things I found that were the primary cause of this.

1) Bad battery, low voltage drops, poor grounds, more likely poor battery terminals.

2) Bad ECU.

3) Bad BCM(body control module).


On Mine when the gauges stopped worked I would leave the battery disconnected for a little while, reconnect it and it would start working. Once I left the battery fully charged for a few days the problem when away and never came back.

Now before that happened when the gauges went dead I was unable to program a new key for the vehicle. I bought the Jeep at auction and it came with a sentry key that wouldn't keep the vehicle running. I had figured they didn't bother to program the chip when they made a key for it. I had a new key made by a mobile locksmith and it worked for 12 hours. I called him up the next day and got him to program a brand new key again for me for just the cost of the key. 12 hours later it stopped working.

Eventually I found a company that would remove the sentry key software from the ECU and let it be run without the SKIM connected to the bus(the SKIM is the halo antenna that surrounds the key lock cylinder) because I thought it was bad.

Later the guage problem popped up and and started suspecting the BCM. But first I suspected the ECU, the ECU I got was exchange, I sent them mine to rebuild and they sent me a rebuilt unit programmed to my vin without the SKIM software. I thought maybe they sent me a bad ECU that didn't crop up untill it was powered up for a while.

Then I figured it might be the BCM being bad so I would try to replace that first, from what I read online the BCM needed to be programmed with a dealer DRBIII tool with the vin for the vehicle otherwise it wouldn't run. I figured I would test that information out before conceeding defeat, I pulled a BCM at a junkyard, but never got the chance to install it, I reset it by disconnecting the battery for a few hours/overnight, it worked and I kept the battery fully charged after that by running it often.

So if I were you I would do a few things:

(I'm assuming your new alternator is good, as I suspect you are)
Clean your battery terminals. Go buy a nice wire bush or a wirebrush battery terminal cleaner and clean those suckers up good.

I've had batteries that I KNEW were bad, would not start the Jeep after 30-40 mins of running a radio. But once they left to sit for a few hours they would recoup to where they would start the vehicle. So just because the battery tests good doesn't mean it is good. (but this is also quite odd consider your problems go away with the alternator disconnected, the voltage the alternator puts out is controlled via a voltage regulator in the ECU, the alternator is really a generator.)

That being said, how old is your battery? Look for a production date or sticker on the battery, it might be an old battery that should be replaced anyways.

The two next things are more expensive. The ECU and the BCM.

The ECU is actually cheaper than the BCM, a company offers a sentry key delete on a good ECU for $125, and a rebuilt ECU programmed to your VIN for $225, both exchange.

The next is the BCM, which you would either need to buy new, have a dealer install and program. Think $1000+. You could buy a used BCM and try to put it in and see if everything works correctly and that it doesn't need to be programmed for the ECU, if not, take the Jeep to a dealer and have them programn the vin into the ECU.

I have a spare BCM sitting around here, if you would like I could send it to you with a refundable deposit. If it doesn't solve your problem or needs programmed to the ECU then return it for a full refund. If does work your welcome to buy it from me if we can agreed on a fair price based on what others sell for. If it does work and you don't want to buy it from me return it for your full deposit. I'm not looking to make money here, I'm feeling generous and willing to help my fellow Jeeper for the good Karma it will bring me.

Let me know if all of that made sense, or you need me to clarify something.
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Old 07-01-2011, 03:24 AM
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Re: PCI Bus Issue

what is your charging system voltage... iirc the ngc controller uses an internal regulator to the pcm. I know crazy voltage can cause all kinds of weird things, and if the pcm is failed... OR you have a shorted wire somewhere causing a full fielding of the alternator you may be well above 14v with the alternator plugged in.

Honestly, and this is expesive so dont go throwing parts... but the last 2 I have seen with similar concerns, dead gauges, no bus were from a failed pcm. This is something I have not seen on the WJ's at all, seems to be a dakota, durango thing... unplug the powersteering pressure switch and look in the connector...if its full of p/s fluid next get to your pcm connectors and inspect them, another no bus pcm I have replaced recently was on a dakota and it was from a failed p/s pressure switch that pushed fluid up to the pcm where it over time made its way into the pcm and killed it... Again, I have NEVER seen this happen on a wj personally but worth a glance.

thinking about it... it seems I heard of water intrusion dripping onto the bcm, and other connectors under the dash straight down from the corners of the windshield... I cannot for the life of me remember exactly what it was on though as it was pointed out to me as a common problem but I havent seen it since.
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Old 07-01-2011, 04:23 AM
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Re: PCI Bus Issue

Thanks for your very useful posts. I'll check a couple of these in the morning both alternators have measured 13.9 and 14.0 volts while operating. AC volts hash output from old alternator was way less than the recommended, as I recall about .05volts.

Many thanks for your kind offer Sir Sam. Will check and put battery on full charge for a day or so and retry.
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Old 07-08-2011, 04:09 PM
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Re: PCI Bus Issue

Hi, Has anyone got a copy of the wiring diagrams for the 2000 WJ Grand that can be attached to post? I was thinking of putting a stabilised power supply direct onto the computer modules using DC/DC converter. Unit such as www.powerstream.com PST-SR500 depending on current demand. This will hold comptuer and comms bus volts steady even with low battery volts.
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Old 01-29-2012, 04:29 AM
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Re: PCI Bus Issue

Hi,

After about 6 months of driving with no gauges etc have finally got his sorted. Purchased a replacement ECU from wrecker for $250 and had independant ECU expert reprogramme to my vehicle. So far all good, used an ECU from same model and quite close part nos mine was 869AB and I used an 868AB. No faults so far and reprogramming only took him about 5mins while I waited.

Thanks again for all the advice and replies recieved.
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Old 02-01-2012, 03:02 AM
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Re: PCI Bus Issue

Hi There,

For several months I have had a similar problem with my 2000 Jeep Grand Cherokee dashboard not working most of the time. Sometimes it randomly works, other times I can get it to work by disconnecting the battery cable for a few minutes.
This is certainly a frustrating problem and from what I've researched online it seems to be fairly common in the early WJ JGC.
After doing all the checks listed in this thread and more, it turns out it is caused by the PCM failing to put out the proper voltage level at the PCI bus.
I was able to finally figure out what was happening by connecting an oscilloscope to the PCI bus and measuring the voltage levels from all the PCI signals found at the PCI diagnostic port which is located under the dashboard by the steering column.
Turns out the problem was the PCI signal coming from the PCM, it was a couple of volts lower than the normal signal voltage ( ~7V ) needed for proper PCI bus operation.

Using an oscilloscope to check for the correct signal levels for all the modules attached to the bus is really the sure way to troubleshoot this type of problem as these PCI modules seem to loose their drive strength and put out a lower voltage rather than just fail open or shorted.

In any case, I just got a used PCM to try, now I need to figure out where to have it reflashed for my car, as the local Chrysler dealer does not reflash "used" PCM's, now looks like that'll be another ordeal..

If anyone know where to have a "used" jeep PCM reflashed, any leads would be greatly appreciated.

@Caprice
You mentioned you had your new PCM reflashed, would you mind sharing where it was done and how much did it cost?


-James
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