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Discussion Starter #1 (Edited)
Vehicle: 2000 Jeep Grand Cherokee Laredo
Engine: 4.0L Straight 6
Transmission: 42RE

PCI Bus Modules Available On Diagnostic Junction Port For My Vehicle:

Pin 1: Powertrain Control Module (PCM), Passenger Door Module (PDM), Sentry Key Immobilizer (SKIM)

TCM is also on this circuit but it doesn't apply to my vehicle. TCMs are only on 4.7s AFAIK.

Pin 2: Driver Door Module (DDM), Controller Anti-lock Brakes (CAB), Electronic Vehicle Information Center (EVIC)

Pin 3: AZC (I have manual controls, this doesn't apply to me)

Pin 4: Radio (Aftermarket Radio installed, PCI BUS wire not connected to anything)

Pin 5: Airbag Control Module (ACM)

Pin 6: Instrument Cluster (IC)

Pin 7: Not Applicable

Pin 8: Body Control Module (BCM)

Pin 9: Diagnostic Link Connector (DLC)

Pin 10: Not Applicable



So I just wanted to list all the modules above that apply to my vehicle and also everything that talks to each other through the PCI Bus. My goal with my problem is to help educate those that may have the same problems because I have been reading multiple posts here and many other sites through Google and it seems that information is scattered everywhere.



Symptoms: AC doesn't work but blows normal, Instrument Cluster Christmas Tree, Power Windows/Door/Locks don't work, EVIC blank

Other symptoms possibly not related: Liftgate Ajar doesn't show on EVIC with both Liftgate/Glass opened nor do they light up interior lights and the driver's door doesn't light up interior lights



So there are things that I've done like disconnecting modules, measuring the voltage on Pin 2 of the DLC etc. The voltage is around 5-7 volts. 0 usually indicates ground/open. Battery voltage indicates shortage to battery voltage.



A module is pulling voltage as far as I can see. The BCM has been replaced with a Ebay BCM with same part number. I have another BCM from ebay on the way in the mail just in case.


Modules I've disconnected: SKIM, PDM, DDM, IC, AC (I didn't know this had no PCI BUS since manual), Radio (PCI BUS wire disconnected so doesn't matter?), I tried the CAB (controller for anti-lock brakes) today and no change. The only thing I haven't tried is the ACM (Airbag Control Module). Could try tomorrow since I noticed the BCM grounds itself there. I obviously lack diagnostic discipline and it's why I need help.



With that said. I'm mechanically inclined and somewhat knowledgeable about electrical so I was wondering if someone had time to walk me through troubleshooting this issue. So far I can say that if I disconnect the battery that the issue goes away completely. Everything functions and works except the other symptoms that may not be related that I stated above.



After about 3-4 hours; the issues all come back. It happens without fail 100% of the time. I'd be willing to provide pictures and possibly a PCI Bus guide later on for others. I have access to a factory service manual with wiring diagrams etc. I do not personally have a DRB-III tool but I can get it scanned if needed at the dealership for a low fee.



I figure that I could probably diagnose this myself provided I had enough time but with full time days at work and stuff to do on the weekends I need a second or third opinion on where I should start and go step by step.



These forums have been very helpful to me so far. I picked up this vehicle for $1250 from a local BHPH with 130k miles on the odometer. It's got the death wobble (will fix in the future as this isn't my daily driver for obvious reasons) and one of the front calipers had to be replaced. Yes it's ATE :-( Will probably do pads/rotors/calipers all around eventually.



So if anyone is willing to give me a hand I can follow directions 100% and maybe over time we can work through this. I am not opposed to getting a PCM down the road if it turns out to be that. Not too expensive.



Thanks for the help if anyone contributes. I promise to write a guide or at least document everything here for future members/google searches. I'll figure this out either way :) I hope....
 

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The beast from Brazil
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Welcome to the garage.
The symptoms you described seem to come from a frozen BCM. I would have a look in the drivers door rubber boot for any chaved wire or even a broken wire (which happens a lot there)
 

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Discussion Starter #3 (Edited)
Alright. I got the boot pulled inside the kick panel still on the wires. I got the white connector off by just reversing it and fitting it over the main connector. How do I get the wires out of the boot itself? Please tell me it's not like heat shrink and it was on before they put the connectors on....

Here's some pictures, looks like something was taped up already.

Can see taped up wire here:

http://imgur.com/RJC7429

Here's rubber boot in between wiring going behind kick panel and the connector. Anyway to get boot completely off without cutting wires or the boot itself?

http://imgur.com/r5zMn7u

I felt the wires and looked at each one. They don't seem to be broken at all. When I was disconnecting the two big white connectors near the hood latch I noticed the bolts holding both of them on were loose. Not sure if that'll change anything. There was a electric brake wire under the dash touching the metal body.... not sure if that did anything but I taped it off.

I think I'm satisfied with the condition of the wires. Short of lopping them all off and rewiring them; I think they're fine.




I went ahead and tightened all the white big connectors (driver's side seemed loose), passenger's side was fine. I checked wires in both boots and saw no breaks. The black tape part I ripped off and it was just two wires taped together; it was the same for both boots. I am not sure why they did that. She's all buttoned back up completely and I reconnected battery and all seems well. We'll see if it lasts. What a pain in the ass problem this is.
 

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The beast from Brazil
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The access to the wires in the boot is a real PITA. Yes, the boots must have been put on before the connector was put on the wires.
I thought that normal bus voltage was around 2V. Does the engine still run when the problem is there?
The liftgate/flipperglas problem seems to be related to your problem, since the ajar info goes to the BCM.
Strange the wires connected and taped inside the door boots. Did you check which wires it are?
Did you already check connector C200 up in the passengers footwell area? This one is known to cause problems due to water ingress due leaking windshield seal. The green corrosion stuff probably causes a short in between the connector pins. Worth to check.
 

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Discussion Starter #5 (Edited)
C200 was clean and dry. I checked the one below/above it; I know there's two there and it was fine. I also checked/tightened these ones plus the ones in the driver's kick panel. All 4 were completely clean.

The engine runs like a champ regardless of the instrument cluster/power windows and locks not working/ac not working. When I turn the key on in the ignition; the instrument cluster doesn't light up like a Christmas tree. It's only when it is running that it starts to mess up.

Pin#2 DLC Voltage with key off is 0.5-2.5V, normal range.
Pin#2 DLC Voltage with engine running is 6v which is a suspected module holding it there. It doesn't fluctuate much from that voltage.

I stayed up late last night doing site: insertjeepforums with my problem and it's starting to look like a bad PCM.

I went to a garage that I've known that was able to pull codes and I got P1686 and P1687. No Bus communication with SKIM and no bus communication with MIC.


But I've had both modules pulled and it didn't change a single thing. Vehicles runs fine, no stalling so I don't suspect the SKIM really. And the instrument cluster tests fine, DOESN'T show 'no bus' error.



It's a really interesting problem and while it's a pain I'm having a fun time trying to figure it out. Swapping out the PCM would be pretty cheap since the BCM has already been swapped and it still shows the same symptoms before and after the swap.



Someone in a thread suggested that I take the PCM out, visually inspect it for corrosion. I guess they're known for bad internal soldering or something? I'll clean the connectors as well while it's out and see if that solves anything.

I also heard that you can measure the PCI BUS wire off of the PCM and see what kind of voltage it's putting out. Battery holds at around 12.6 and Alternator puts out about 13.6 to 13.8 and maybe a little more depending on rpm. I don't really suspect the alternator as the battery has never been dead. There's is 0 parasitic draw with a multimeter hooked in between negative cable and battery negative. It puts everything to sleep and it's like 0.01 amps? or maybe that's mAmps.
 

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The beast from Brazil
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I expected the engine to be killed when the bus communication freezes due to a faulty component, but it seems to be not. Could very well be the PCM. What happens if you remove the shorting plug from the diagnostic junction port and measure the bus voltage from the PCM/PDM/SKIM only? Will it still go to around 6 V? If it does, one of those three components is the faulty one. If it doesn´t, then the problem must be something else.
Will be traveling as of today and most probably won´t have internet or only in rare cases. I will be back around the 2nd of October, but will be following your thread as much as possible.
 

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Discussion Starter #7 (Edited)
I will check those out later today. I disconnected battery to pull out the PCM and clean the connections with CRC Electronic Cleaner so the problem won't show up for a few hours until the battery has been connected for a bit. The PCM isn't corroded but IT IS the original PCM back from 2001. There's a date sticker on it. I included a few pictures. I'll see you in a bit then. I'm sure this will be resolved by the time you get back. Thanks for the help!

Imgur: The most awesome images on the Internet

Imgur: The most awesome images on the Internet

I'll be back later to give the results of measuring voltage of pin 1 only in the diagnostic junction port.




I suppose some good news is that there's a nearby PCM for $125 and the Dealership will only charge me $150 to install/program it. I've heard a lot of dealerships won't do this but seems this local one may be hurting for money or treats its customers right. The service guy knew exactly what I was talking about and I own Fords and always ask service guys questions. The local Ford seems oblivious to everything but making money.
 

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Discussion Starter #8 (Edited)
I'm still waiting for the whole thing to get into a dysfunctional state again but I took the Jeep to go get lunch just now. The Sentry Key Light popped on about half a mile down the road and then the Jeep stalled. Had to pull into parking lot and restart. No light now. I do the key juggling and it's coming up with P1685 which will probably disappear if the problem doesn't occur in next x amount of starts.

I also noticed that the mileage is NOT increasing in my instrument cluster. What is going on? I'm assuming bad PCM now because of these two things. Like I said, before and after the same thing is happening with old/replaced used BCM.

Updated: 09/24/2015 - I decided to take her into the dealership for a diagnosis. I've checked a lot of things and there's not much I can do at this point. If it's a wiring issue then so be it; I'll rewire what I have to over time. But if it's a module issue then we should be good to go cause I got a used PCM/BCM on the passenger seat depending on what they need to replace; if it's that. If not then I got backups.

Mileage said 130xxx on the cluster but it's 160xxx something in the BCM. Not many know this but there's a way to see the true mileage through the transmission which is what I'll have them program it to. Well, I'll update this post when I know what's going on from the dealership.
 

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Discussion Starter #9 (Edited)
Just got called from the dealership. New alternator needed and new battery cables. The technician said he disconnected the alternator wire to isolate the vehicle working on its own and everything popped back to life. I believe there's a voltage regulator inside the PCM but with this working without the alternator... hopefully she's fixed!

I could've replaced both things for around $300 but they only charged me $500 including the diagnosis. So not too bad. We'll see tomorrow what's going on.



It sounds like they're throwing parts at it so I'm taking 30 minutes to see if I want to tell them nevermind or not. I just read a post here of the issue:

http://www.autoinc.org/perplexing-puzzle-grand-cherokee-something-crazy-causes-systems-to-quit/

I may go drop a print off of this and have them dig into it deeper instead of throwing stuff at it.



Update: E-mailed this over for the technician. They're digging deeper into it. At this point I'm thinking it's either A) PCM or B) one of the modules. With an oscilloscope, they should be able to pinpoint it. I personally should've just bought an oscilloscope for 65.00 off ebay. I'll call tomorrow and see where we're at.
 

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Discussion Starter #10 (Edited)
Alright. Been in talks with the service writer and the technician. The technician did a lot of testing and 100% believes that it was a bad alternator and battery cable. Which I've read one post so far where the guy replaced the alternator and it fixed all of the issues. I'm trying to figure out /why/ a bad alternator would cause all the PCI BUS stuff to go crazy if the PCM EVR is working properly.

Here is the post with the guy who put in a new alternator to fix the issue:

http://www.jeepforum.com/forum/f310/wj-electrical-problems-instrument-cluster-windows-heater-evic-alarm-more-1011447/

He had same symptoms as me. Everything works fine when key is in on position, but once it's running everything flips out. Granted; after a battery pull to reset computer... this won't happen for 4-6 hours after in my case. After that time has passed I can recreate the key on/running symptoms 100%.

Regardless I'm waiting until Monday to see if the issue is resolved. Service writer offered to program/install the used PCM I bought for free if issue still persists. My guess is he offered this because he knows the issue is fixed lol.

I'll be back Monday.
 

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The beast from Brazil
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A bad diode in the alternator rectifier, can cause some ripple/noise on the feed lines, so maybe could do something to the PCI bus.
Interresting turn to the story.
 

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Discussion Starter #12
Called just a few minutes ago. Still showing the same symptoms. It was a hail mary by them to throw parts at it but like I said I needed the battery cables because the negative cable was all messed up although still tightened. Didn't need the alternator. I'll chalk them both up as preventative maintenance and probably see where they are at in about 2 and a half hours.

I'm going to ask him to throw the computer in programmed like he said he would and go from there. I'll probably go pick it up. I got an oscilloscope, Powerprobe 4 and ECT 2000 by Powerprobe on the way from Amazon. I'll get this figured out on my own at this point over time. I think I just got a little too frustrated.

I'll update soon.
 

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The beast from Brazil
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Ok, let me know what the PCM change will do, maybe it will just solve the problem.
 

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Discussion Starter #14
Well, I talked to the guy and they're going to work on it for two days more free of charge to find out the problem since they already threw the alternator/battery cable at my vehicle and I doubt I'll be able to get money back out of that so I guess this is there way of justifying it. I'll look at it as preventative maintenance and move on.

I'm going to go pick up my Jeep in two days. It's obvious their electrical guys are highly incompetent and don't know what is going on with it even thogh I've e-mailed them over countless PCI BUS Diagnostic documents that are plastered all over this board and more on how to fix it.

It's funny though. When I picked up the PCM at the local junkyard I was told to use two independent electrical guys instead who had access to DRB III scan tools instead of the dealership. Should've listened. Anyways, I'm out $500 at this point and will just pick it up in two days from now. I shouldn't have got impatient. I probably would've figured this out on my own by now but it's hard working 45-50 hours a week.
 

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Discussion Starter #15
So I just received a call from the Service Writer. They did all the diagnostics off of the information I sent them and they concluded that the Driver's Door Module was electronically locked up. He said the guy went through and programmed each module (assuming he reprogrammed the BCM, possibly PCM too to add 'features'?). Anyways, they've test driven it and let it sit overnight and the modules didn't act up which they normally do after 7 hours of battery being hooked back up.

So they only charged me for only 1 hour of diagnostics and the alternator and battery cable. $505. I think I got off pretty easy but now if someone else with my type of Jeep goes to the same place they'll be able to diagnose it pretty easy for someone else.

If you're in the Tampa area, it's Ferman Jeep of New Port Richey. My service guy was Steve Brawer. Hopefully this helps someone else out. I'm still skeptical that the door module could be 'locked up' persay but we'll see what happens.
 

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Discussion Starter #16 (Edited)
Unfortunately it isn't fixed. I thought maybe with the new alternator that I'd see more than 13.8v charging the battery at idle but I suppose that's normal for these Jeeps since it's only a 4.0 v6. Anyways I guess I'm going to order a $65.00 oscilloscope off of e-bay that runs off a laptop. I'll have to do this myself from scratch.

The symptoms are gone when the key is on and the engine isn't running. As soon as I start the engine all the problems are there with 5v-6v on the PCI Bus line. I may mess with the diagnostic junction port later this weekend with a DVM and see if one of the modules is screaming for attention over the others.

I still have a backup BCM and PCM on the side as well. Still getting P1686/P1687 as well once it's fully messing up. It starts off with sentry key light on and P1687. Could be SKIM. I'll keep everyone updated.







UPDATE: I went to Ford and picked up a Motorcraft Tested Tough MAX BXT-65 850CA/1090CCA battery. So far nothing has came back after replacement. It's weird. The other battery tested fine at 12.6v+ and 13.8v+ while charging. Alternator also put out 13.8v+ from the post.

Is it possible the other battery was internally shorted somehow but not showing up as 10v? Maybe the battery post itself was cracked/broken? I even loaded tested it and it was fine. I don't know. I guess we'll see in the morning if the issues come back.

I called the dealership and told them it wasn't fixed and he said bring it back. So if I can't figure this out by Monday we'll see what they find out again.
 

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The beast from Brazil
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So the problem is related to the running engine. I would disconnect the alternator cable and see what it does with running engine. If ok, then there must be something wrong related to the alternator or charging system. Was the PCM changed? The voltage regulator sits inside the PCM.
 

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Discussion Starter #18 (Edited)
Alright. So I took the cap off of the Diagnostic Junction Port. All the other modules seemed to be doing fine, constant 0.1v on the BCM but we can deal with that later once I hook up my oscilloscope.

I found that on Pin 1 there is a consistent 6-7v from either the PCM/PDM/SKIM. So I'm going to start the vehicle and pull the SKIM connector and then measure it with 3 starts up, maybe 5. Then I'll try the PDM.

This took all of 5 minutes to check. The dealership didn't do jack shit with my vehicle. I'll deal with them once I get this resolved. I'll probably use my oscilloscope a little later. It came in late last night and haven't had time to set it up so I'm using a DVM for now.

I'll be back in a few minutes with results. Pulled the PDM and the SKIM and they went down a little bit but that's probably because that's their operational voltage perhaps. However the voltage was still at 6.6v and 6.2v respectively. I'm guessing because I've got the DJP cap off that the voltage is going down from something being electronically locked.

This is all speculation but with just the PCM on Pin 1 it's still 5.5v. So. This looks like a PCM issue to me and since the dealership will put my used one in and flash it for me.... I could skip the oscilloscope perhaps. Keep in mind this is all tested while running and tested 3-5 times over 5 minutes. I'll keep testing it for another 30 minutes. I'll keep the DJP cap off for now to see if the voltage keeps dropping. Maybe the EVR in the PCM is decreasing itself and putting out lower voltage without the DJP cap on?

I won't know for sure until I oscilloscope it and being at work; I have free time here and there to check stuff but maybe not enough time to use that. Back in a bit.

Actually it really doesn't matter. There's not supposed to be consistent voltage on Pin 1 in the DJP no matter what. Because Pin 1 can be measured through the DLC pin#2 when the cap is put on and it's supposed to be 0.5-2.5v with a DVM. I'm ruling this as the PCM and I'll be dropping this off at the dealership in an hour. As much as I want to use the oscilloscope there's no need at this point. I will be making some videos in the future for the PCI BUS issue because there are hardly any videos out there and there's a lot of our Jeeps out there.

I want to give back to the community. I'll let you know what happens later today. They should have the PCM changed and the PCM flashed by the end of the day.
 

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The beast from Brazil
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I´m not sure if a faulty component can make the PCM increase the bus voltage and stay at that voltage as long as its not reset (by disconnecting the battery). Did you try that already?
Because when i´m not wrong, is it the PCM which supplies the bus voltage, kind of the master in the system.
 

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Discussion Starter #20 (Edited)
The PCM is connected to the PCI BUS from Pin #30 on PCM Connector #3. However, the power looks like it provided by the Junction Block on Connector 3? I've heard of Junction Blocks sometimes going bad but it provides the Data Link Connector with a Fused Battery Supply. It will be something to look into if this doesn't fix the issue which I don't see why it wouldn't. I didn't notice any moisture in the area of the Junction Block/Body Control Module which is another problem. And both big connectors on Driver's Side were free from moisture/corrosion.

I didn't check after resetting the computer by pulling the battery. I've done it multiple times before and all the electronics would work after that and I've measured it then and it was 0.5-2.5 on Pin #2 in DLC.

I got the vehicle down at Jeep now and they're doing it all for free; the computer flashing I mean. We'll see what happens tomorrow after I pick it up. I'll know in 6-7 hours of sitting if it will do it again.

There could be an issue with the body control module but I figure because I used the DVM and not an Oscilloscope.... 0.1v may be normal operation. I need to get that 5-6v off of Pin #1 first.

I thought maybe Crank/Cam/MAP shorting out may do it but I've not had trouble starting it ever. And it's died on me like once which could be due to constantly resetting the computer or something.

I'll keep you updated. They're going to try and get it flashed today but worst case scenario I'll have it tomorrow morning. And I'll let you know what's going on. Testing the DJP with the DVM is probably the best way to figure out what's causing the issue. And even though the issue may be fixed; I'll test it all with an oscilloscope eventually just to get the experience.

Anyways, once this is fixed I'll make a few youtube videos of procedures to check, how to check C200, locations of grounds etc. Seems this information is very rare to find as I've spent 30-50 hours already reading tons of information from google searched.

I'll be back.
 
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