Bought my wife a 96 GC Limited. It had a bad PCM, OBD II scanner said No Link when I tried to pull codes, and the fuel gauge did not work, which from what I have read confirms this. I bought another PCM yesterday and plugged it in and YAY! the gauges all came on. I turned the key to start it did not fire up, but now the gauges are out again, and the OBD II scanner again says no link so it appears that this Jeep has just fried this PCM as well.

I tested the power and grounds to the PCM with the key on and they were correct. That was before I put the new one in.

I did search but I could not find a problem like this one, a lot of problems very similar, but not exactly like it, so please don't think that I posted without searching.

If anyone has a way for me to figure out what wires, or components could cause this please please please, let me know.

We have 2 small children and I hate leaving for work and leaving them without a car, I am nervous all day long that something will happen and they will need to get somewhere but can't.

Thanks in advance guys, it seems like there is a lot of people on here who really know their stuff.

Thanks

 

It is likely a ground issue. When you moved it around connecting cables the other PCM may have been receiving a good ground but starting the engine may have caused it to lose that ground again.

Just a theory.

 

Welcome to CF.
The FSM states that the Body Control Module controls the instrument cluster and communicates with the PCM over the CCD bus.
Circuit A250 from fuse 11 in the Power Distribution Center powers circuit F75 through fuse 7 in the junction block. Circuit F75 supplies battery voltage to the BCM. Circuits Z1 and Z2 provide ground for the BCM.

 

Thanks guys.

Any hidden grounds, or common grounds that get nasty that should be thoroughly tested that I should pay special attention too?

 

Not sure if you have a 4.0 or the V8 but on the 4.0 there's a ground on the right side of the engine on a lug just rear of the distributor. It will have a metal clip holding the wiring harness and behind that metal clip is a ring terminal with a ground wire for the PCM it can get dirty/oily and loose over time.

 

Its a V8.

Should have stated that from the beginning I guess.


The fusebox does look a bit corroded, but everything seems to power up ok. And the fuses are all good.

I wish this was simple, If anyone has had this same problem please feel free to chime in.

 

i had pretty much the same problem, so il try to explain this the best i can, for me i would put the key in and nothing worked but the interior lights. what i ended up having to do was hot wire it by taking a wire straight from the battery to the ignition key switch. the bottom of the key switch (under the steering wheel) there is a plug of wires that go into the key switch, we looked at a manual and found the ones that supply power, so we tested them and they held 12v like they where supposed to, but when we turned the key it would drop to nothing.... so thats what i did, i hope it helps, 1996 grand cherokee limited V8

 

I had a similar problem with a 300ZX a few years back, but it wasn't burning out PCMs, it was just making the relays go all stupid, and blowing fuses, so this problem is a lot more pricey than replacing a a 20 AMP fuse a few times till I tracked it down. One other thing I just noticed is that along the drivers side plastic sill plate that I popped off, the screws were rusted, and the Jeep does have a sunroof, could this cause a problem with corrosion anywhere that would lead to these symptoms?