Moderately High Voltage

Got a '95 XJ running with some high voltage. It's been cold up here in Ontario and my voltage has been running into the red for the winter. Just burnt out my alternator, which I have replaced. Not sure where to start looking for a solution. Battery tested fine, grounds look ok, all similar issues I've looked at don't seem to fit quite right. Picking up a multimeter tomorrow to start testing some spots.


First time posting here, so not sure I got the formatting right. I've tried searching, but none of the threads I find are close enough or understandable for me.


Thanks in advance.

Sorry, just to clarify - it's just in the lower end of the red on the gauge.
Never goes above or close to max.

Definitely double check with volt meter, instrument cluster gauge is notoriously inaccurate. Mine shows just above the red on the lower scale but is perfect voltage when checked with actual meter.

jumbotront said:

Got a '95 XJ running with some high voltage. It's been cold up here in Ontario and my voltage has been running into the red for the winter. Just burnt out my alternator, which I have replaced. Not sure where to start looking for a solution. Battery tested fine, grounds look ok, all similar issues I've looked at don't seem to fit quite right. Picking up a multimeter tomorrow to start testing some spots.


First time posting here, so not sure I got the formatting right. I've tried searching, but none of the threads I find are close enough or understandable for me.


Thanks in advance.

Click to expand...

If your alternator burnt out, that seem to indicate a problem somewhere. Take a good look from the battery outward. inspect and clean every connector and tighten securely. Also check or replace the cable/s from the alternator to the PDM (Power Distribution Module) or fuse box. I think on that year the alternator wire is split into two with two 60 AMP fuses in the PDM. Check that both are intact. Or was/is it two fusible links instead of fuses? I forget which it is. It is worth taking a look at that.

The alternator on your XJ is controlled by the computer. If it detects low voltage anywhere in the system it will try to get the alternator put out more and more power thus overdriving the alternator.

Pin 9 at your PCM is the power in should show nearly battery voltage with key in run position. Possible there is some corrosion resistance in that circuit fooling the voltage regulator. Check the red wire at the battery end of your PDC under the plastic cover and make sure the bolt is tight.
Check the voltage at the battery terminals with the engine running and see how accurate your gauge is.

Thanks for the responses.


Checked the fuses (two 60AMP) and connection at the end of the PDC, all good there. Cleaned up all the grounds and other connections best I could. Tried to check continuity of the wire that heads to the computer for voltage regulation, but not entirely sure where it attaches to the alternator.



Multimeter shows voltage at ~14.8v pretty consistently now, gauge seems to show the same. Bit high still? Before the winter it seemed to stay always on 14.


Appreciate the help so far.



Lord save me.

jumbotront said:

Thanks for the responses.


Checked the fuses (two 60AMP) and connection at the end of the PDC, all good there. Cleaned up all the grounds and other connections best I could. Tried to check continuity of the wire that heads to the computer for voltage regulation, but not entirely sure where it attaches to the alternator.



Multimeter shows voltage at ~14.8v pretty consistently now, gauge seems to show the same. Bit high still? Before the winter it seemed to stay always on 14.


Appreciate the help so far.



Lord save me.

Click to expand...

Glad you made some progress. 14.8 is about .5 volt on the high side. 14.3 is considered perfect and 14.5 acceptable.
There are two small wires at the back of the alternator in a plastic block. One get + voltage when the ignition is on. The other is a ground from the computer. The computer toggles this wire on and off to regulate the voltage. If the ground from the computer stays high the voltage will keep going up,...some claim to see as much as 19 volts.

Sorry, my XJ workshop manual is for the 1996 year model. That year the computer changed to the 3 connector version so the pinouts would not be accurate. Try to clean the connector pins on the computer and give the wires a once over to see if you missed something.