I recently bought a 2000 Jeep Cherokee Sport, 126K mi.
The other morning, as I was driving about 45 mph, the "Check Gauges" light came on, and the Voltage Gauge topped out at 19V, and remained there. When I came to a stop, at the traffic light, the warning lamp went out, and the gauge leveled out at 14V. It remained normal, until I got on the highway-- then the same issue recurred, and did not return to normal until I came to a stop again. It was wet outside that day, if that helps with anything.
I tested the battery and the alternator, and they both passed.
Since then, the problem has yet to recur again.
I know the voltage regulator is integrated to the PCM, and the vehicle employs a battery temp sensor, but am not sure of the parameters of these components, in order to successfully test them.
Has anyone seen this before, and/or have any ideas about this issue?
Thanks for any input.

 

i dont believe the regulator is integrated into the pcm on the H.O. engines.

sounds like to me you're alternator is going bad.... is the battery swollen at all?

 

The battery is not swollen.

Everything I've seen about the voltage regulator states that's in the PCM (AllData). I'm not sure what the criteria is, that determines whether or not I even have an H.O. engine, but what I do know is: the Alternator comes in 3 different max amperage output ratings for that year. Mine is the highest, at 124A.

 

91 and up 4.0 = H.O. must be nice having the 124 amp alternator. you cant put it on one of the 4.0 s with the lower amperage with out modification...

 

and it is apparently in the pcm. but the alternator is suspect for overcharging, and a bad battery can do it also... check grounds

 

Yes, the alternator seems to be the obvious answer, I know, but the fact that it shot to 19 volts on the gauge makes me think that it would've been apparent through the vehicle electrics-- like all the lights would've gotten brighter or something. This is why I feel like maybe it's not even a matter of actual overcharging, rather than a faulty signal to the instrument cluster. Also, it only happened twice, during the same 20-mile drive cycle-- and not since then. My experience with alternators tells me that, usually, when one goes bad, the problem is constant & consistent. I'm a technician at a Mercedes-Benz dealer, so I had access to really good test equipment for the battery and alternator, and they both passed with flying colors. I bought an alternator anyway, but am hesitant to install it, fearing I may be wasting $150. I don't like to just "throw" parts at cars, and haven't been able to prove where the fault is occurring. I was just hoping maybe someone had seen this before. I appreciate your thoughts on the issue. I'm tempted to connect several test leads to my Jeep, in a way that I could swap them in & out of a DMM while driving, to find where the voltage fault is occurring-- but that's a pain in the ***.