Vehicle is a 2000 Grand Cherokee limited w/4.7 v8. Over 250k miles on car, runs nice (at least it used to).
Guage on dash seems to indicate the voltage and it's misleading. On a fresh battery it fools the technician into thinking the battery is charging as the level looks like it's in the proper range. The garage hooks their meters up and tell me it's charging.
The battery went dead, I had the garage put in a new battery and since the cables had been hacked by previous owner I had them put in all new cables. Battery went dead again. I had them put in a new alternator as it too was old and didn't seem to be putting out.
After all of the above, on way home from the shop after replacement of the alternator, the guage started dropping from ~14v towards ~11v. Now I'm being told I have a multi-choice of computers to replace? What the hell? And now the overhead console next to the mirror is also all different in it's menu. Is this a related problem or symptom too?
I am having trouble trying to find which computer(s) and where are they located on the car.
How many computers are required to run a car anyway? I'm told there are 5 on this Jeep. My 1969 pickup runs just fine and doesn't use any computers.

 

There are multiple computing modules, but the PCM (Powertrain Control Module) is the king. It's on the passenger's firewall in a bracket with 3 big gang plugs going to it. The jeep works on a data buss system where all the modules talk to one another. The only other 2 that I'm aware of are the Body Control Module and the Transmission Control Module. There are also 2 periferals, The Security Key Identification Module and the Keyless Entry Module.

Check ALL your grounds and ALL your fuses. The alternator regulator is inside the PCM, but loose or weak connections can reak havoc with the system. You can do a parasitic draw test to find out what's draining your battery (Google it) Worst come to worst, you can have a dealer do an electrical system diagnosis for $100. An awful lot of mechanics like to change the computer because it's an expensive part and too many times it is the problem, but I'd hate to spend that kind of money because of a simple bad connection, which will probably still be there after a computer change.

I almost forgot! underneath the battery there is a battery temperature sensor that tells the PCM when it battery gets hot. Then the PCM cuts back the charge rate to control the temp. It could be faulty. Very few people even know it's there.

BTW, your jeep is a WJ, not WK2. The WK2 was built 2011-2020.

 

Yup. What Dave said. Clean your connections, especially your grounds. See my sig, #1. There's a reason it's #1.




That's "wreak havoc".

 

[this is a 2000 grand cherokee with 4.7 v8.]
I had the repair shop replace the battery cables with new that were made up at the CarQuest store and install new battery, new alternator. It looked real professional. The alternator field wires were dangling by themselves (didn't like that part of the job) and I had found a reference to the battery temperature sensor as possible cause of not charging. So I pulled it all apart and found a knife cut right through the blue field wire near the headlamp. Got out the soldering gun and vinyl tape. I checked the temperature sensor and read 11.26k ohms across it, and am thinking it's probably working. Would be nice to know what range it should really read as. I took every ground-wire I could find off, and wire-brushed it too shiny and put silicone grease on it and bolt then tightened it down again.

Put the battery box, fuses, wires all back together and after charging the dead battery all night, I started the car and the alternator started putting out 68 amps. (dc clamp-on ammeter). Here is where it's weird, about 3-5 amps are going to the battery, the rest disappears into the fuse box. Everything is more or less off in the car. AC is set to 72, fan on low, it's around 68 outside. Headlamps are off, doors are closed, seat-heaters are off, defrost is off, stereo is off. What is sucking down 600watts of power and not making smoke? Battery seems to hold a charge overnight ok.

Been driving the car back and forth to town, seems to run fine. The overhead console has a different menu, choices are missing. Interior lamps don't come on with open doors anymore. Where is this computer located?

I found what may be the PCM, mounted by the radiator overflow jug on the right fender? Didn't see any thing with wires going to it on the firewall, though. Where are the other computers located? The ABS system seems to quite often behave like the rotors are warped as braking at high-speeds can be a little unnerving, slow speed usually has no indication of a warped rotor. Don't know where this computer is located either.

 

I believe the Body Control Module is located under the dash somewhere near the center. The ABS pump and control module is underneath the master cylinder near the bottom of the car.

 

"Here is where it's weird, about 3-5 amps are going to the battery, the rest disappears into the fuse box."

Inspector Cousineau says this is not possible. Suspect the clamp on DC meter. Are you sure it's really a DC ammeter? Those are pricey. The AC ones are much more common, do you have one of those?