Rdytodive

I have a 1999 grand Cherokee Laredo and when you start it up gauges work fine and within a min they all drop out one at time and all lights come on have tried everything does anyone have a fix for this is it the cluster or something else?

Noah911

What happens when you pull the battery cables and touch them together for several seconds to short out and reset the PCM? Does the issue resolve itself for a little while afterwards?

I would recommend to get a read on what the voltage is at the Data Link Connector (DLC) PCI Data BUS circuit off the #2 pin at the DLC, and see what this can tell you... It is essentially you and your multimeter acting to replicate a diagnostics scan procedure how it would normally be getting done with a high-end DRBIII scanner. Has there been a DRBIII linked up to the DLC since having the cluster gauges problem?

Is there anything else funny going on with it? Do all of the windows and locks function how they should? Have you checked out all operations; such as the air conditioning and heater functions, electric seats, cruise control, the compass, etc... Does everything else work how it should?

Rdytodive

I havent tried shorting the two cables together yes a high end scanner was put on it but couldn’t get it to communicate with the Jeep I have changed the bcm to get the windows door locks compass overhead console and power mirrors to work but gauges still don’t will see what happens when putting the two cables together does tomorrow

Noah911

If the scanner did not communicate with the Jeep, then most likely you do indeed have a data BUS issue.

Check for having the normal fluctuating 2.5 VOLTS on the DLC PCI BUS pin #2, is how to see it...

Rdytodive

Okay pulled the battery cables and held them together for about 30 seconds. Checked the wiring under the hood and all grounds. Everything seems okay there but the gauges still do the same thing. Any other suggestions or do I try another cluster to eliminate it. Could it be the pcm?

Noah911

It could be the cluster is the reason. I think replacing it may definitely be able to solve the issue. That would only be a guess though... It could be it, maybe?

It could also be any of the other modules to cause an issue such as this too. Or, any of the wiring associated with any of the modules. One of the things designed to occur on the overall system is for the cluster gauges to drop-out whenever there is a data BUS issue. It could be only just a sign.. more so than a symptom of the problem. If that makes sense? It does not have to be per protocol though, as all bets are off whenever there is a problem happening on the data BUS communications system. The ABS light is supposed to remain illuminated as another sign. Of course, the ABS lamp does not have to stay illuminated. Maybe all of the other warning lamps stay lit abnormally instead. Or, it could be the ABS lamp is unable to remain illuminated if there is a certain type of problem occurring, possibly with the ABS module itself, or any number of other possibilities, etc...

You have a 1999 WJ Grand Cherokee? The WJ has a PCI BUS. The #2 pin of the DLC is for the PCI BUS of a WJ for it to be able and communicate with a scanner for diagnostic purposes. The diagnostic BUS wire terminates at the #2 DLC pin on the WJ. You can use the #2 pin here at the DLC to test and see if the BUS system has a healthy voltage on it or not.

The absolute first step which should be done for something like this.. is attempting to obtaine a voltage reading of the PCI data BUS diagnostic circuit. Ussually, this is done at the #2 pin of the DLC. Anywhere along this particular wires path and length is actually fine to use though. Depending on what you find for voltage on this wire/#2 DLC pin, this will determine the appropriate next steps to be taken from there. If it is too high (very likely), too low, or non-existent will make a difference on what you are supposed to do next when trying to figure out what is the reason.

Rdytodive

If I’m looking correctly at the plug correctly #2 has 12volts on it I have on with 4 and change on it and one with 14 while engine is running I don’t have any pin with that low of voltage I’m using a power probe 4 on it
also tried another set of gauges that was working and they did the same thing as the original gauges

Noah911

Let me understand better to make sure of what you did when you got the 12 VOLTS reading.

Did you use a voltmeter.. and touch one of the meter leads probing at the #2 pin of the DLC, and touching the other meter lead to a good metal grounding point on the chassis when you got this reading?

Is the reading you are getting at the #2 pin of the DLC always a steady 12 VOLTS? There is not any voltage fluctuation occuring any at all on it?


This is a picture of the WJ DLC showing you exactly which pins are which.

You can either test it with the red voltmeter lead touched to and probing at the #2 pin, and touch the other black voltmeter lead to probe the #4 pin for use as a ground... Or, probe the #2 pin with the red voltmeter lead, and touch the other black voltmeter lead to any good metal chassis grounding point. I would try doing it both ways just for comparisons sake. Both of them are legitimate ways to carry out the testing procedure how you are wanting to get it done for this reading.

If you have a steady 12 VOLTS, and it is not fluctuating any at all? Then, you just figured out the specific reason for why the problem of your gauges is happening. Having 12 VOLTS at the #2 pin of the DLC is one of the results you would expect see.. in order to know for sure that there is definitely a problem/fault located on the PCI data BUS. There are three or four different results you would expect to find when there is a PCI data BUS failure. Having a steady 12 VOLTS is one of those... It means the data BUS of your Jeep has a short to battery voltage on it.

Is that what it is.. a steady 12 VOLTS on the #2 pin?

Rdytodive

I will double check that tomorrow I was using a power probe that hooks to the battery and will detect power or ground on whatever wire you put it on it is computer safe but will get the voltmeter out and use it

Noah911

I see what you were saying. I think I just misunderstood it at first with how you were saying it. The power probe IV is the tool you were using. I have seen those types of testers (I just looked it up). Those are really nice! I have never used one before though. I am just not very familiar with using something like that is all. I think I will probably be getting myself one of those sometime soon. If it says there is 12 VOLTS on pin #2, that would definitely be showing you what the problem is...

If it is 12V... It is possible the exact reason could prove difficult to track down. There is just no easy way to go hunting for the reason of why this type of problem is happening on the system. There are steps to follow in a certain order unplugging all of the different modules one by one, and rechecking the BUS voltage. If you get down to having no modules left remaining as being plugged in, and you still have the 12 VOLTS, then you may have to trace every inch of the entire BUS wire to find the wire fault.. if finding the high voltage is not coming from any of the modules being internally shorted when unplugging all of them.

Other things to consider are arcing of starter, alternator, secondary ignition, and the main battery power and grounds how they are loomed together. It would be worth it to at least look over those main battery wires in the loom pulling off the tape and checking that their insulation looks intact, and is not heat scorched and causing arcing to occur. As well as doing the same for all of the other larger gauge wiring. And to spend a few minutes to give a good general look over all of the main wiring harnesses looking for any signs of something abnormal. Such as any spot having rubbed through along a portion of it to cause a short or compromised wiring insulation.

The next first step after seeing if the 12V is there on the #2 pin is to start unplugging all of the modules one at a time though, and rechecking the voltage after each one of them gets unplugged.

Noah911

I would recommend to start with the Transmission Control Module (TCM). Unplugging this module first. I believe the TCM is the most likely reason for having a failed data BUS resulting in having all of the gauges drop out. The TCM is one of the dominant nodes (modules).

I would begin with unplugging all of the dominant nodes first, before moving onto the recessive nodes. The Airbag Control Module (AM), Body Control Module (BCM), Passenger Door Module (PDM), Mechanical Instrument Cluster (MIC), Controller Antilock Brakes (CAB) are a few more of the dominant nodes... I put them down in the order I would choose to go about unplugging them if it were me.

Even if the BCM was very recently replaced, this does not mean everything with it is okay. If you were to unplug the BCM and find a normal PCI BUS voltage on the #2 pin after doing so... Then, you would begin to investigate with this module and at its location next. Just because unplugging a module makes the BUS voltage return to normal does not mean it is a corrupted module either. For example, it is very possible that the PDM is the corrupt module in this hypothetical scenario. It could be the PDM is influencing the BCM to to have an influence on and is destroying the integrity of the overall data BUS due to the way in which these two nodes are situated on the system. Or, it could be that the BUS wiring associated to the BCM is where the fault is actually located. Or, it could be the PDM wiring (or the other driver side door wiring is what is influencing the PDM) is where the actual fault is located to influence the PDM to have an influence on the BCM to shut down data BUS communications.

All of this if there is 12 VOLTS found at the #2 pin.

If there was actually a primary fault which was initially influencing the BCM to cause those other issues how they were occurring at first. Since replacing the BCM fixed those other issues. This obviously means there is still a fault somewhere with the gauges acting the way they are. This fault may be able to cause issues to occur at the BCM again, and destroy the newly installed BCM over time if it goes unrepaired, and is left the way it is.

If you find a pinout diagram for the PCM connectors. You could unplug each modules associated wires at the pins to remove them from the system easier and quicker this way. I believe you would still need to find a BUS diagram of all the different modules in order to see which of them are neighboring modules to those associated modules at the pins you were unplugging. And then go from there to unplug those other modules one at a time to see if it is actually a neighbor module to the one from the disconnected module of the pin you just unplugged. That, and I believe the same thing also applies for with the BCM. If it were the BCM being unplugged that fixed the voltage. It could possibly help to isolate the reason in this same similar way, by unplugging all of the wires one at a time there at the BCM too.

Rdytodive

Thank you for the information. I will start going thru the system one at a time. And check the voltage. Will let you know what I find it is pouring rain here for the next few days so do t know if I will be able to work on it after work but will try.

Noah911

One other thing to try if you wanted. If you were to unplug the alternator and run the Jeep without it. It is possible you will see the symptoms dissapear and the gauges will come back alive for you. I would try it. This does not mean the alternator is the reason though. It just means the alternators electrical field is strongly coordinating itself to the strange voltage already on the data BUS is all.

Rdytodive

Will do. Also I’ve always been worried about disconnecting the air bag module is it safe to disconnect it and if so is there a process to go thru to do it and I haven’t found a Tcm under the hood where would it be and can I disconnect the pcm to see if it might be the problem to if I can’t find it anywhere else

Noah911

I think having fear of the airbag anytime when you are working near to or at the steering column, or with any of the associated components to the airbag is a very good thing. The airbag can be dangerous and really hurt someone badly if something were to go wrong with it whenever working on or near it. To disable the airbag you should disconnect and isolate the negative battery cable.. and then wait a minimum of five minutes before beginning any work while you let the airbag capacitor naturally discharge itself. It takes two full minutes to discharge the capacitor. I personally recommend waiting for a full five minutes to be safe.

I am not 100% sure on all of the modules where they are located? I would have to look it up. For in case you have to dig deep into this thing with all of the modules and wiring, I recommend for you to download the Factory Service Manual (FSM) for your Jeep from a website. I believe one of the free FSM downloads comes from a site called something like 'jeeponlinemanual.com', or something very similar to it. You will probably be glad you did as you may need it...

(edited to add):
You can disconnect the PCM. The general rule of thumb is to leave the PCM connected until very last though. I am not 100% sure how much of a difference it would make on a PCI BUS. This BUS has termination resistors in each and every module vs one of the othe data BUS systems Chrysler uses (a CCD BUS). I still think the PCM of a PCI system probably has some sort of primary and backup roles incorporated into it which should most likely be maintained throughout the testing. I am no expert on these systems. I just know a little bit about them from some prior research I have done.