Losing voltage while driving

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KaseriD

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I apologize in advance. I'm a new member and not a car guru by any means. I'm trying to figure out if I can repair my jeep without having to sell an organ.

Two weeks ago my jeep threw up a "check gauges" warning and I went from 14v while driving to the gauge being stuck at 9v. I was a block from my destination so I limped it home. I turned it off and tried to restart it but it was completely dead. I took the battery to get tested and was told I had a bad cell so I replaced it. That solved the immediate problem and the jeep started but was now still slowly losing power while driving. Roughly 1v every 30 minutes. On advice from a friend, I replaced the alternator in hopes of fixing it but the problem still exists.

At this point, I know I'm going to need a mechanic but I'm hoping to get an idea of what could be wrong. Any help would be appreciated. My jeep is a 06 Wrangler Rubicon.

(Posted with mobile so please forgive any format issues)
 
First, remove and clean the entire battery harness and clean the lugs and grounds (battery, alternator, PDC, starter, engine block, firewall) and also the battery posts. Then take a look at the alternator wiring harness for chafing. The wiring runs from the alternator, over the dipstick tube mounting bracket to the block, up to the fire wall and over to the PCM.

The regulator is inside the PCM but there are good odds that field wire is shorting to ground. If you cycle the ignition from OFF to ON three times any stored codes will be displayed in the odometer readout. I'll bet you get P0622.
 
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Also check the condition of the three 32 pin harness connectors for the PCM. If one of them has dirty pins or a loose connector this could cause a similar problem.
A few weeks after purchasing my '01 Sport I was driving down the highway around 65-70 mph and all of a sudden there was a noticeable loss of engine power and the engine just shut off. I signaled and started heading for the shoulder. About 10 seconds later the engine restarted. This same situation occurred twice before I tracked it down to dirty pins and one of the two connector retaining tabs was not snapped.
To resolve my problem I disconnected each harness connector from the PCM and reattached multiple times to clean the pins and ensure the connector tabs were snapped in place.
 
Less. Before, it was consistently near 14v at start. Now, it starts at about 12v and slowly drops. I can recharge the battery and it comes back to about 12v.
 
KaseriD said:
Less. Before, it was consistently near 14v at start. Now, it starts at about 12v and slowly drops. I can recharge the battery and it comes back to about 12v.
Click to expand...

Okay, so if it's at 14v your alternator is charging your battery. With the engine off or alternator dead your battery gauge will read 12v or less as the battery drains. So this suggests your alternator isn't charging.

Check the cables going into the alternator and make sure all polarity is correct. Check that it's properly grounded. Check that the fusible link hasn't been blown.

What style of battery connector do you have? Pics would help
 
How would I check if the link was blown?

All the cables seem to be intact and properly attached but I'm not mechanically inclined. I've attached pictures of all the cable ends I could find. The wires are wrapped together in a plastic tube.

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You still should clean the wiring harness and grounds. The alternator grounds to that oil covered bolt on the engine block. Also, notice the wires resting on the dipstick bracket?

When I had similar issues I found that the wiring harness had rubbed against the engine block until the field wire grounded out.

View attachment 164778
 
This is what my gauge starts at. I'm not able to check my wires completely right now but I'll look them over tomorrow. Thank you all for the advice. I love this old jeep and I want to keep it running for as long as I can. It's my first and only vehicle that I want to keep if I can.

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With the engine off you can check voltage from the + side of the battery to the +side of the alternator to rule out that cable. If you see 12v or so then the cable is good. If you don't the cable needs to be replaced. Next to look at is the connector out the back of the alternator and what controls those wires.
 
I know this is an old thread.
Just to help share intuition, my daughter's 97 TJ started to have low voltage. It would fade after 15 minutes and start trailing down to 12v, then suddenly drop to 9 and Check Gauges light would come on. Within 2 weeks, it got to where it would still start fine but fade slowly to 12v after about 30 seconds and then eventually always suddenly drop to 9 with Check Guages. Battery tested healthy 12.6v with jeep turned off. I thoroughly cleaned the battery connectors & terminals with no change. I ran down to Advance Auto and they tested the battery to be good. I had 3 spare alternators (my wife, kids and I have 5 Wranglers) so I threw one in and that resolved the issue.
 
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