Chrysler Repair: 97 Jeep GC Laredo 4L 6 Cyl, coolant temp, jeep line

Question
Dear Roland:

Our 97 Jeep GCL has hit the 150k mark with a thud. Starting to replace everything, radiator, muffler, water pump, coolant temp sensor.

Recently (july) had trouble starting which was fixed with new coolant temp sensor.

Now again wont start, all the time on first try.  Yesterday would not start and wife had someone jump start it and on the drive home the volt gauge was at 19V. once home, the battery was again dead in a few hours.

I was going to replace the alternator and read in my Haynes manual that the PCM does the voltage regulation.  

Now thinking to replace PCM instead of alternator as altenator is below AC motor and looks like a knucklebuster.

Haynes manual suggests PCM is behind coolant overflow tank, but does not look like it to me.

Do you know where it is.  If I replace it, does it require VIN and milage to be inputed via computer? I am unable to do this. Will it not run well without this input?

Thanks a million

David

Answer
Hi David,
I unfortunately do not have/claim expertise with the Jeep line of vehicles so I can't tell you exactly where it is. Generally in the other Chrysler vehicles it is on the left side near the inner fender and should have one or two multi-pin plugs (total wires probably 60 or 80). It may run but probably not well, and maybe not at all without the correct programming of some technical aspects of the vehicle which it is operating.
If your battery is approaching the end of its warranteed life you could very well replace that and see if the voltage output drops back to normal (14-15V). I would also suggest getting a fault code readout of the memory of the present PCM after the battery is replaced and you have driven it for a few trips. The fault codes cancel when you disconnect the battery so this will give you a fresh reading of what may be wrong. Autozone parts stores often offer to do that for free, or an independent shop will do it for $40 or less. Ask for the numbers of the codes, what they mean, and what they recommend doing. Then let me know and we'll evaluate that if you like.
The PCM does regulate the voltage output but so too would a short to ground of the wire that runs from the PCM to the alternator do the same thing, so check around the alternator wires to be sure none have damaged insulation.
Good luck on getting things going right again.
Roland