Battery light/ charging issue

[Black98transam]

Posted this in the electronics section but think maybe that was the wrong area.

02 liberty 3.7 165K miles

Other day my wife was driving and the battery light came on. Did not come on again for several days. While driving home one night the interior lights dimmed, headlights, taillights, etc all eventually shut off. Wife got home and jeep sat for a few days for christmas.

I drive the vehicle 20 miles yesterday no issues. Stop at advanced and have battery and alternator tested both pass but battery was said to be towards the end of it's life. As I am driving the battery light comes on halfway home. I get home check a few things and go to start the car. Will not start due to dead battery. Take battery to be tested and it tests fine take it home to charge. Remove alternator to have it tested and it tests fine. Come back reinstall it, clean connections (they were pretty good to begin with) check a couple grounds (all good) look for any bad wires (can't find any). Put the battery back in and go drive the radio, lights, heat on and everything is working. Drive for about 45 minutes and no issues. Park in my driveway and leave it running for an hour and no issue.

I'm not thinking I fixed my issue at all. I'm guessing the battery currently has enough juice (charged to about 70%) to run everything and that is why I have not had any issues.

I think it's the alternator that is the problem. I have done some research and have seen it suggested that the alternator can not be properly tested by auto parts stores is that correct?

If I get the battery light on and take to an auto part store to have it tested would they be able to give me an accurate reading on if the alternator is bad?

Could the battery temp sensor be causing this?

Could a gunky connection or lose ground cause this and I magically fixed it by cleaning it up?

Is it likely it's the PCM causing this?

 

[HoosierJeeper]

Not sure on how to test the alternator. But they are simple to replace and not expensive. I got a 50k mile one from a junkyard for $40, none of the reman or new ones get good reviews. Got 150k from my stock one before the bearings shit the bed. If it hasn't acted up again since you cleaned it up, I wouldn't worry about it.

If the battery is more than 3 years old I'd replace it. Mine went from being at 60% capacity to dead over night. I've never gotten more than 3 years from a battery in the 10 years I've had the KJ. If the alternator was really bad, you wouldn't have been able to drive it for 45 mins or idle for an hour.

Where in WI are you? I'm in La Crosse.

 

[Dave]

Check battery first. I bought my KJ new in 05. OEM battery crapped out and I replaced it with a NAPA premium one that lasted about 5 years (longer than HJ but he has a winch) and then I just replaced it with another NAPA premium one. They seem to last a while for me anyway.


Dave

 

[renegade 04]

I would have the alternator tested at a place that rebuilds them.

 

[JasonJ]

I would have the alternator tested at a place that rebuilds them.

Most of the charging system testing equipment is pretty standard. The one we had at Autozone when I worked there years ago was actually pretty advanced.

Although, isn't the voltage regulator on the KJ built into the PCM? So testing that off the vehicle will be nigh impossible...

OP's comments about the problem sound more like intermittent bad connections, or the VR flaking out from time to time. I highly doubt one could drive 45 miles on a dead alternator or VR.

Blck98transam, what are your actual voltage readings from the vehicle? Test key off engine off, key on engine off, key on engine on, at idle and at 2000-2500rpm. I'd also like to know the system voltage when it is exhibiting the dead/no-start condition.

In fact, I'd also connect a scan tool or a real voltmeter to monitor while driving as well.

 

[LibertyTC]

"OP quote"" Tested -both passed, but battery was said to be towards the end of it's life"

How exactly did they test the battery & alt anyways? When Jeep is running what is the voltage reading at battery?
Load tested electronically or ?...Battery should be fully manually charged before a load test.
I got one of these..applies 100 amp load and gives you a CCA reading pretty accurately!
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Hydrometer
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Will tell you the state of charge and if the battery needs re-charging. Also will show a weak cell real quick.
Batteries suffer in cold weather & it's when they will often crap out!~
Close to end of life means get a new 800 CCA battery in group34/78 and even consider a sealed AGM type. AGM as completely sealed, wont offer corrosion to terminals.
Here is the Midtronics load tester on a new AGM battery- Really good Cold cranking amps!
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[renegade 04]

The jeeps voltage regulator is part of the ECM, and thus if it has a problem then they want you to replace the whole thing, but you can wire up a external voltage regulator like me and be on your way as well.