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High Voltage

vabeachtennis

NAXJA Forum User
Location
Va Beach
I was driving my 1996 4.0 2WD this afternoon and I started to see my voltage creep up past 14 volts and it slowly went on it's way to maybe 15 volts. My GEN light went on but I kept driving. I picked up my wife and we started driving back home and the volts went back to 14 (it usually hovers just below 14 unless it was a cold day) and the GEN light turned off for the 17 mile ride back home. I checked the battery and the voltage was approximate 12.75 volts.

I've searched and saw threads where the volts have been up to 19. Mine didn't get that close but it was enough to ask if anyone has any ideas. I know that the voltage regulator is supposed to be with the ECM for this year. I've had the alternator fail on me but the voltage progressively went down on the desperate ride back home.
 
Usually that's a ground connection issue, start by cleaning all the connections including the regulator(ECU) connections.
 
Usually High Voltage is due to a bad ground (negative) connection. But that is inconsistent with it gradually creeping up like you saw. When you checked the voltage and it was 12.75V, was that while the gauge was reading 15V and the GEN light was on or after it went back down?
 
Usually High Voltage is due to a bad ground (negative) connection. But that is inconsistent with it gradually creeping up like you saw. When you checked the voltage and it was 12.75V, was that while the gauge was reading 15V and the GEN light was on or after it went back down?


The readings were after it was turned off in my parking lot. It's been sitting for a while and has run flawlessly for 300+ miles. The gauge looked like how it would look when you start it in the winter but went just above that 14.7 threshold and triggered the GEN light. It was also odd that it stayed at 14 the rest of the way home when it usually stays at 13.7. At least it made it home! :)
 
I started the Jeep up again and the voltage read 13.75. The only very minute change in the readings occurred after I moved the ground from the battery to the passenger side fender back and forth. The change was from 13.74 to 13.76.
 
Yeah that sounds like what it should be. It would be interesting to see what the actual voltage was when you were seeing 15V. I don't completely trust the gauges on the dash to be true readingd. For example, the Temp gauge will stick at 210 even while the real temp goes above that, and then suddenly peg high once the jeep overheats. What you describe sounds like there might actually be something causing overvoltage, but that's a unlikely failure to have. I guess yeah clean the contacts/grounds and see if it happens again.
 
That's not the gauges fault, that's just water boiling.
No, it is the Gauges fault because if you hook up an OBDII reader it'll show the temp climbing to 220 and 230 while the gauge still says 210. It was a "feature" to calm down paranoid drivers, but is annoying for guys like us working on 20-30 year old Jeeps trying to diagnose problems.
 
Wow, didn't know that. That's annoying as hell. Is this all model years? When I was having heat troubles it smoothly went past 210 to 220.
 
Usually High Voltage is due to a bad ground (negative) connection. But that is inconsistent with it gradually creeping up like you saw. When you checked the voltage and it was 12.75V, was that while the gauge was reading 15V and the GEN light was on or after it went back down?


I didn't answer your question correctly. The GEN light turned off as soon as the voltage reading went back to 14V.
 
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