Auxiliary Battery Jump

[ShadowsPapa]

If I've been wrong about repeating what I read/learned or thought I did, I'd want to know.
Too many unknowns, too many mysteries with this - and with how my own is behaving with things, the more I know, the better.
It's bad enough not being able to get a dealer to even believe something isn't right but it's frustrating not knowing myself in detail how this works or doesn't work.

The dealer notes on mine indicate that they got to the PCR to isolate the aux battery, charge and then test it.
If a person got to the primary or coil leads on this - that would show the state at various times.

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[Radio Guy]

If I've been wrong about repeating what I read/learned or thought I did, I'd want to know.
Too many unknowns, too many mysteries with this - and with how my own is behaving with things, the more I know, the better.
It's bad enough not being able to get a dealer to even believe something isn't right but it's frustrating not knowing myself in detail how this works or doesn't work.

The dealer notes on mine indicate that they got to the PCR to isolate the aux battery, charge and then test it.
If a person got to the primary or coil leads on this - that would show the state at various times.

I don't want to take too much stuff apart to expose the relay and test so if there is any info available on where the ESS relay coil wire goes, like to the fuse box, etc, that would help me a lot.

 

[ShadowsPapa]

It's fuse F42, 5 amps, but that's not really going to help as the fuse would be hot on both sides all the time. (at least I'd expect it to be)

EDIT - if you pulled F3, that post or terminal N3 would be cold when the PCR was open.
With the PCR closed, it would be hot as it would be connected to the aux +
Fuse removed, it would isolate the aux + from the alternator output as well as the main battery.
When that fuse blows, the aux battery isn't charged by the alt and there's no power to the aux battery from the main battery via N2 to the fuse and N3.
So, pull the fuse, N3 should be hot only when PCR is closed.

Long day, so maybe I'm missing something.

 

[Radio Guy]

And another thing, I kind of remember tracing the the main wire from the alternator directly to the main battery but the diagram a few posts up shows the alternator connecting to the N7 terminal. I can verify this tomorrow.

 

[ShadowsPapa]

And another thing, I kind of remember tracing the the main wire from the alternator directly to the main battery but the diagram a few posts up shows the alternator connecting to the N7 terminal. I can verify this tomorrow.

I grabbed those diagrams from other posts - MAYBE they are older or are Grand Cherokee or Wrangler, whatever. I've not traced the alt output wire.

 

[ZoMojave]

I grabbed those diagrams from other posts - MAYBE they are older or are Grand Cherokee or Wrangler, whatever. I've not traced the alt output wire.

But Bill, if those diagrams came from other posts, how can the accuracy be determined?

 

[ShadowsPapa]

Trolling trolling trolling.......................

You are just upset because an experienced auto tech is contradicting you and a few others and in the process upending your beliefs on other things.

I know the source, I've verified many of these things personally, a Wrangler guy who has done a lot of research on the system posted a lot about the operation of the ESS and dual battery system. He's no slouch himself.
The only question now appears to be PCR operation.
I also have diagrams of the IBS system from FCA as some STAR training documents.

 

[Radio Guy]

I grabbed those diagrams from other posts - MAYBE they are older or are Grand Cherokee or Wrangler, whatever. I've not traced the alt output wire.

I traced it tonight and it goes into the fuse box area and not to the main battery in my 2021 Mojave.

 

[ShadowsPapa]

I traced it tonight and it goes into the fuse box area and not to the main battery in my 2021 Mojave.

I had the charger on mine and when I went back out to close things up, verified as well, 2020 model year.
I am seeing more and more people with issues with these, and have been doing more research. I've seen one with a stored code indicating low voltage and another that logged with jscan a low state of charge. I think we'd see more if people weren't disabling ESS - because that's one of the first indications of a problem.

 

[Radio Guy]

I found a 2020-2022 JT fuse box legend that says this:
F42 – 10 Amp Red Power Control Relay Control Feed (Electric Stop/Start)

I'll measure that fuse before and during cranking to see if its a constant voltage, meaning the fuse is before the ESS system or if its between the ESS smarts and the ESS relay. Worst case I'll have to dig down to the ESS relay and measure it directly but I want to avoid that.

 

[ShadowsPapa]

I found a 2020-2022 JT fuse box legend that says this:
F42 – 10 Amp Red Power Control Relay Control Feed (Electric Stop/Start)

I'll measure that fuse before and during cranking to see if its a constant voltage, meaning the fuse is before the ESS system or if its between the ESS smarts and the ESS relay. Worst case I'll have to dig down to the ESS relay and measure it directly but I want to avoid that.

I read the wrong column - it is 10 amp, not 5 like I said earlier. This is from my own fuse cover->

 

[JKJ]

I’ll be renewing my AAA membership tomorrow after reading this thread. Probably post my jumper cables in the “for sale“ section too.

 

[Radio Guy]

I’ll be renewing my AAA membership tomorrow after reading this thread. Probably post my jumper cables in the “for sale“ section too.

No matter which direction the ESS testing goes there will be an easy way to overcome a dead AUX battery. I suspect it will be what's already out there, a simple jumper across N1 and N2 in the fuse box. I might even consider a lockable high current switch like this across N1 and N2. Mount it so it sticks out the side of the fuse box.
https://www.ebay.com/itm/223115980332?hash=item33f2bfae2c:g:Jk8AAOSwuvVbgE54

 

[jebiruph]

This video shows that the JL can cold start from just the aux battery

I've found that there is a brief (instantaneous) separation of the batteries that tests the aux battery prior to both batteries participating in a cold start.

I'll vouch for this diagram, it's mine and is based on the schematics found here. https://www.jlwranglerforums.com/JL-Wiring-Diagrams/STARTING_CHARGING-SYSTEM---2.0L_3.6L---ESS.pdf

 

[jebiruph]

No matter which direction the ESS testing goes there will be an easy way to overcome a dead AUX battery. I suspect it will be what's already out there, a simple jumper across N1 and N2 in the fuse box. I might even consider a lockable high current switch like this across N1 and N2. Mount it so it sticks out the side of the fuse box.
https://www.ebay.com/itm/223115980332?hash=item33f2bfae2c:g:Jk8AAOSwuvVbgE54

20A is not enough current capacity for an N1 - N2 jumper, experience shows it should be at least 40A. It should also be fused as there is the possibility of it getting shorted out, and once it's fused the switch is redundant. That's how the fused bypass jumper came into existence. https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

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