Noah911

I wish there was a diagram out there. I do not think it would be one single diagram as it is too complicated a system. Finding some sort of all inclusive list, or diagrams of the central hub branches of the PCI would be nice.

Something like this is out there somewhere for sure. I have not been able to find it in the past. It must be top secret clearance stuff for some reason? I will see what I can find on it though. The best source for PCI BUS information I have found comes from the training manuals used by the Fiat-Chrystler Performance institution. Except, they are for all of the many data BUS set-ups they use in all of their vehicles, and are not specific to the Grand or the Cherokee's.. is the problem. You have to figure out what type of daisy chain or whatever it is they used in which years on which models to know what you are looking at, and even then it is still non-specific and is difficult to understand.

Does your Jeep have Remote Keyless Entry (RKE)? Some Jeep models have a circuit board for this module located in the overhead dome light (it is in different locations for different years). The RKE is another common one which I have read has caused this same problem for others too.

Does your Jeep chime at you when the door is opened with key left in the ignition? There is a door chime module located somewhere for this function.

Is there an overhead console with an Electronic Vehicle Information Center (EVIC) to display temperature and direction, and a few other things? If so, the EVIC is a module itself.. and essentially so is everything it links with to communicate. The temperature sensor is a thermal resistor but, with the way it is wired through the BCM to the EVIC it acts the same as a module would being able to (it can) cause BUS issues. The same thing applies with anything else on the Jeep displaying information even if there is no EVIC. Such as the Oil Pressure Sender Unit and some of the other 5 VOLT sensors.... if they are wired in certain ways for alerts. I do not know if it is all of the 5 VOLT sensors or not? It would make sense though, because they route to either the BCM or through the PCM to display their information. If the voltage is normal on the data line BUS, I do not see any other way to check for this except if the gauges start working or if you use a oscilloscope to see electrical noise on it.. and unplugging every 5 VOLT sensor one by one.

Does your Jeep have Cruise Control? There is a Clockspring in the steering wheel which communicates on the data BUS. The Clockspring can cause electrical noise and issues over the data line to disrupt communications between systems because of how it is wired. This has come up several times about it on this site. Never for with a BUS issue though. Although, I definitely think it could.

It does not have a Transmission Contol Module? Is yours a manually operated Jeep?

There is the Ignition Control Module (ICM) and the Fuel Module still.. . There is a Transfer Case Module as well, if your Jeep has 4×4.

I am not sure if I remember it.. but, is yours a WJ Grand Cherokee. The WJ headlamps are modular headlamps in designe. They are Headlamp Modules. Does your Jeep chime at you if you leave your headlamps turned on and put the ignition switch to off? Do the headlamps turn themselves off after 8 minutes when left on after the Jeep gets shut down?

The rear tail lights are also modular in design with a circuit board in them too.

There is a module for the interior lights on WJs which turns them off after a set timeframe if they get left on, if yours is a WJ (I'll have to look.. maybe you said if it is a WJ).

I think the only way to figure out what all of the modules truly are is going to be by looking at many multiple different sources, and gathering together the information putting it into a list.

Have you tried a DRBIII scanner to look again if it is able to communicate? It could be you have recently fixed the issue for why it would not communicate before by fixing the PCM wire short, maybe?

Noah911

It might be good to pull the battery cable and check the resistance of the BUS line. The modules all have a certain termination resistance to them. There is an equation I saw once which helps in determining wether it is a primary or secondary module(s) problem. It would just be more information possibly could be put to use if finding that equation again somewhere. Not sure if it would really be helpful right now though?

Rdytodive

I have a friend that works for dodge I will check with him and see if I can get any kind of diagram. It is a wj. I think an oscilloscope is the answer right now. Will let you know.

Superscan811

Had a similar issue with the windows, A/C and power mirrors not functioning.
Checked the door wiring and it all looked good.
Replaced the door module but the problem was still there.

There was also an intermittent issue where the Automatic transmission seemed to be partially in 2 gears as the engine would bog down and the transmission would get very hot.
It felt like I had the park brake on.

I removed the BCM, replaced the surface mount 220µF Electrolytic capacitor (for $0.80) and re- soldered both sets of connector pins.
There was very little solder on the connector pins from factory, so I suspect it was a dry solder joint that was causing these issues.

If you are handy with a soldering Iron, it would be worth doing this before you buy another BCM.

So far, it all seems to be working fine.

Cheers.

pzolan

This is an amazing thread, I have this same intermittent problem with my 1999 Jeep GC with the 4.0. If I remove the ground from the battery for a day or so, then reconnect it, everything works great. But over a couple days the gauges start to drop out, sometimes the windows don't work, sometimes the interior lights stay on, sometimes the AC stops working, sometimes some or all of the gauges drop out, and sometimes they start to come back as I drive. Key word is obviously "sometimes", this isn't the same problem each week. I need to go back through this thread and follow the troubleshooting information, this is great information!