As title states im in serious need of help. Was driving along in my 98 12 valve when i lost all input from the cluster. I have done self check and the cluster passed and gives codes 920-921-999. I have cleaned grounds in engine bay, have a brand new vin coded pcm swapped in a different engine harness that i went through and cleaned every connection and re wrapped. I have swapped in a cluster from another 98 as well as a 99 24 valve. I have un plugged modules without any change checked relays swapped them around as well as checked fuses. One thing that is odd is usually everything i read with regards to no bus is the lack of a WTS light. On my truck KOEO the WTS and OD off are lit up immediately and dont go out then after a bit i get ABS/Brake, Low Fuel, and the seatbelt warning light. I really need help figuring this out to get my cluster back, this happened maybe 15 mins after i was messing with my pillar pod guages and one of then shorted out and popped the fuse tap that it was in, fuse 14 in the junction block but everything else worked fine and I’ve replaced that fuse and my glow shift guages function properly as well as all other electronics on the truck. Any help is greatly appreciated 

See if you can find a 5 volt line coming out of the PCM the auto tranny trucks have it but yours may not have a wire in that hole.

 

I think the tach sensor on the front of the 12 valve uses 5 volts too. That sensor wiring on the 12valve gets all oily and the insulation falls apart. You might try unplugging it.

 

The PCM also interacts with the AC clutch if your AC worked before but not now that's another sign.

 

It's looking like your PCM is dead.

  On 2/27/2024 at 3:10 AM, Great work! said:

See if you can find a 5 volt line coming out of the PCM the auto tranny trucks have it but yours may not have a wire in that hole.

 

I think the tach sensor on the front of the 12 valve uses 5 volts too. That sensor wiring on the 12valve gets all oily and the insulation falls apart. You might try unplugging it.

 

The PCM also interacts with the AC clutch if your AC worked before but not now that's another sign.

 

It's looking like your PCM is dead.

Ill check the 5v reference i stripped this harness down and cleaned everything re tapped and then loomed it. This PCM is new its the 3rd one ive tried but i can have it rechecked by the builder it has a warranty and hes only 2hrs from me. I have the auto wiring but its tucked away not used

I have 5v at the ESS, Ground is 0 ohms. I really think it has to do with the WTS/OD light circuit both are connected by fuse 14 in the junction box. But if i pull that fuse both still light up witch im not understanding how thats possible? But again im not the best with electrical diagrams.

 

Per the FSM both go through that fuse then to cluster then to the PCM im not sure if the PCM is grounding the circuit or what but i feel like if there was a way to test this circuit id find something. With having a 5 speed why would that light come on and its on immediately it just doesnt make any sense to me. Im hoping there is a way i can test the wiring for this somehow?

 

Edit: ok so i see the ground for everything seems to go from C1 to G200/201 witch i assume is the grounding up by the parking brake/kick panel. I will be getting ohm readings for that as well as trying to clean everything. 
 

As far as everything goes through the diagnostics we’ve determined 

 

PCM has power

PCM has ground

PCM is sending 5v reference 

CCD Bus is at +/- .02v (actual readings ~2.53/2.55v witch could be my meter but lets just call it good for now)

Cluster has power

Joint connector 7 cleaned and reseated

Joint connector 6 cleaned and reseated

 

im curious if the fact we are getting bus bias does that rule out the possibility of the cluster being the culprit? Also i really dont think its PCM related, it started with my original pcm then i swapped in one from a working 98 12v that didnt change anything. This pcm i got from a builder was vin programmed and flashed and verified working and i had batteries unhooked when i put it in.

 

Those diagrams are often simplified. They don't show all the inner workings of black boxes. The circuit board has additional parts like voltage regulators and dimmer circuit.  It only is giving you a clue that a ground is needed to trigger the light.

 

Disconnect all 3 connections at the PCM and see if the lights turn off. Is the panel stuck in a self test, lamp check mode? Have you tried a different one?

 

The PCM and cluster both have 2.5 volt bias circuits built in. the other modules don't. 

If i disconnect pcm lights are off, what do you mean like stuck in the self check from holding the trip meter then turning the key. If so then no, both of my clusters show the same thing

I disconnected C2 PCM witch has the WTS driver. Turned key OD light is on immediately WTS is off. Started engine cluster still dead

Is it possible to have the PCM plugs swapped I never tried it. Definitely disconnect the batteries first. They are different colors but maybe not keyed.

 

Use a flashlight and inspect the PCM pins and sockets in the plugs look for any thing bent or burned or sockets pushed back into the plugs.

 

I prefer old school test light instead of meter for doing power work. If you have one recheck both power inputs to the PCM and ground.

 

Interesting, I'm playing with a cluster in my lab and notice different lights come on and off based on if I have both grounds connected or just one at a time. Cluster C1 pins 4 and 5. Double check them for grounds.

 

BTW, @Mopar1973Man our wiring diagrams have an error. The OD off light wire is missing. It should be going from cluster C1 pin 7 to PCM C3 pin 6.

 

To go much further than this you will need an oscilloscope,  just a cheap USB dual channel one will work. But you will just go crazy. LoL.

I dont think they can be swapped around i think they are grooved to go only one way. I will re check power to PCM. I kinda am already going crazy i wish there was a way to get just the speedo and tach working it just doesnt make sense with what its doing. The only thing i can say cluster wise is when i have the original cluster in the odometer just blinks and the wts and od light are one immediately. If i put in the cluster from a 99 vp truck i will get no bus on the odometer as well as check engine light but the OD off light doesnt come on even though it lights up for cluster check showing its there. The VP cluster came from a manual truck that i got my trans from my truck originally was a 47re automatic i wonder why the lights are different between the 2 but both give me the same 2 codes

 

 

when i checked C1 i went from the ground pin to the pin for power can’t remember the number i turned the key on and had my meter bridge the 2 pins and got 12.4v but i will double check grounds tomorrow 

Plugs look good at pcm no burns or anything 

Sounds crazy but clean and reconnect your battery terminals. Strange things happen on these trucks related to battery terminals. I'm running out of ideas.

 

Try the home run wiring or unwrap the harness from the cluster plugs , headlight switch and the point were your glowshift unit was tapped in. Unwrap down to the fuse block. Look for melted wire.

 

Alternator noise? Try disabling it.

Yeah im about out of ideas as well ill try terminals and the grounds by the kick panel. Is there a easy way to get that wiring to where its visible or no

I ohmed the circuit from g200 to cluster for ground and from fuse 14 to the corresponding pins for WTS and OD it came out 0 resistance. So that leaves cluster or PCM I believe as the issue correct? With the cluster out can i test the 2 ccd bus pins in c1 for voltage or will that not work. But if its cluster why would the 99 cluster not work or are they incompatible 

There's no easy way to get in the harness there. The PCM provides 2.5 volt bias too so check for it at the cluster plug with it unplugged. The basic guages work the same through the years but some lights and features change. Many Chrysler cars and jeeps use the same CCD bus.

 

The bus works both ways the cluster send messages to the PCM like when the trip button is pressed and the status of the MIl and airbag lights.

I will test the bus for the cluster then and see what i get

.5/.6 v in pin 9 and 10 of C1 with PCM connected 

No bias at ABS module either

Im gonna send the pcm to the builder tomorrow hes going to test it for me for communication and put it in a test truck

What else should i check this is definitely a good indicator 

Since the PCM is putting out five volts to the sensors that's a good sign it's getting good power to it.

That is my thought but it is not giving me bias for the bus

Pcm is in the mail, noticed my aftermarket fuel level guage isnt reading anymore im guessing it has to do with the connection saying sensor return? Would that be a ground or 12v supply?

Returns are really dedicated grounds. The fuel tank is plastic so it needs grounded but it's good practice to keep high current grounds such as an in tank fuel pump and a sensitive sensor ground separate. 

Update on my PCM, got a text just now PCM was DOA according to builder. He told me to recheck all grounds and harness since he doesnt have another core if something fries this one. But he verified the replacement is working and communicating. So what should i triple check before installing PCM to make sure its not a installation error

I would say you already did all that with your troubleshooting.  Do check your battery voltage while running since you did an external regulator. High voltage can ruin it.