FIXED - dead battery, voltage regulator issue

[00 Trans Ram]

There are already a lot of threads on this, so probably won't be much discussion. Just wanted to put something on here so it'll show up in searches.

Got home from vacation and had a dead battery (2020 JLUD). Used a spare battery to jump start. Started up and ran fine. Monitored voltage while driving and noticed that, under acceleration, while maintaining speed, and while parked, voltage would drop to 12.0-12.2 volts. But while coasting at speed, voltage would go up to 13.7-14.2.

Went to auto parts store and they diagnosed a faulty voltage regulator. Voltage regulator is built into the alternator, and alternators for the diesel are $600-$800. Brought it to Jeep for a recall and had them hook up their diagnostic tool. They said the tool said it was the voltage regulator. But, the tech said that sometimes this issue can be caused by the aux battery.

Got home and removed fuse F42 and disconnected the negative aux battery cable (taped it off). Started and went for a drive. Voltage stayed at 13.7-14.2 the whole time. Problem fixed!

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[CaJLMetalHead]

that stupid AUX battery is nothing but trouble

 

[Reinen]

It's actually not fixed. Staying 13.7-14.2 the whole time means that your alternator is constantly trying (and failing) to charge the battery. Your batteries are bad. It should be around 12.6-12.8v and occasionally jumping to 14-14.3v to recharge when not accelerating.

I'd also venture to guess that your ESS is not working. That's the first thing to go with bad batteries. It will refuse to kick in when batteries fail voltage testing. It has nothing to do with the Aux battery, it's both of them.

 

[00 Trans Ram]

It's actually not fixed. Staying 13.7-14.2 the whole time means that your alternator is constantly trying (and failing) to charge the battery. Your batteries are bad. It should be around 12.6-12.8v and occasionally jumping to 14-14.3v to recharge when not accelerating.

I'd also venture to guess that your ESS is not working. That's the first thing to go with bad batteries. It will refuse to kick in when batteries fail voltage testing. It has nothing to do with the Aux battery, it's both of them.

Battery is still good. Less than a year old. Went back to auto store and had them perform another test and everything is showing up green.

 

[speedymart]

Just so you know the diesels will sometimes take over a minute to actually put charging voltage out. Even disregarding the diesel part, these vehicle can and will maintain 12.6-12.8v by design. They only increase if they need to re-charge the battery or additional load is needed.

If you have ANY charging issue you WILL get a DTC for it and if it's large enough the battery light will illuminate indicating it. The battery light staying on while running will only ever indicate a charging issue, nothing else.

Based on your symptoms you either have a draw or one of the batteries is going bad. If you let the vehicle sit and it had a dead battery this kind of tells you what happened, honestly. A scan tool would've told you immediately if the alternator was failing by comparing the voltage sense to the target charging voltage. This would 100% be associated with a accompanying DTC. I'd bet 50 bucks the gentleman doing your recall had no idea this feature even exists with witech.

 

[Jeffy56]

Remember, the system has "smart charging". Under most conditions, after start and warm up, normal electrical load, the charging voltage will be lower under acceleration, then rise while coasting. Cruise anywhere in between. i.e. 12.5 acceleration, 14.5 coast going down hill is what I've seen in the display.

https://www.jlwranglerforums.com/fo...oltage-display-for-ess-battery-health.113355/

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