So I had trouble and took the 98 ZJ ( 4.0 I6 ) to a service center.

Their tester indicates a GOOD BATTERY but " Low Voltage From Alternator ".

I told the guy " the alternator is externally regulated, can you test the regulator? "

He was a new kid and wasn't sure, but he did know how to use the machine.

Symptoms do indicate charging system trouble --- run the jeep all day and OK, but run it for extended time with HEADLIGHTS ON ( high load ) and the battery runs down.


Before I install a new ALTERNATOR is there any way to test the VOLTAGE REGULATOR ????
I know the regulator is on the PCM.


THANKS !!!!!!

Why replace battery if alternators not operating properly just replace alternator never really heard of any regulators going bad in Pcms .. just saying

Opps ... I meant before I change the ALTERNATOR


I know it is rare but a search indicate a few have had to swap out the PCM due to failed regulator.

I bought a new ALTERNATOR ...

It is a 120 Amp Bosch Reman

They asked if I wanted 90 Amp or 120 Amp .

I figure bigger is better!

Just hope it fits in fine!

Be aware there is a temp sensor underneath the battery that tells the PCM to cut back alternator output if the battery gets too hot. They have been known to go bad.

Hey Dave, what do you mean there is a temp sensor under the battery location? What year range ZJ does this cover and what does it look like? Is it the button looking thing or a mat design?

My 97 ZJ had one. The alternator was overcharging the battery and was boiling the acid away. I was alerted to this by someone on CJ. Changed it, cured problem. Yes. its a button looking thing under the center of the battery. Mine was white with corrosion.

huh never knew what that thingy was. pretty cool

Thanks ..... maybe I'll throw one of them in just for good measure.

My guess is that it is a THERMAL SWITCH.

Do you know if it is " Normally Open " or " Normally Closed "?

Knowing that would make testing, possible.

I am going to guess it is " Normally Closed ".

Thanks

Have you checked the diodes as well?

I didn't know about the temp sensor. The guy at advance auto ran a test and my alt is about gone. Did the bosch higher volt alt work well? any issues?