3.6L ESS Aux Battery Bypass

demisx

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Hey Dee:

This is what, to use your words, I think you may be missing.

Your main battery is connected to N2, agreed? When the 3.6L JL is at rest, (in fact at all times but an instant at start and ESS events) N2 is connected to N1. I think this is what allows both batteries to be charged when they are connected as per factory, and charger cables are solely connected to the two terminals of the main battery when the vehicle is at rest.

So....at rest, N1 is energized from either or both batteries on the positive side--and in your case solely from the main battery because you've disconnected the ESS/Aux battery, and the other end of your tester is on the negative of the main battery. Stated yet another way, in your situation, N1 IS the positive of the main battery.

Provided your main battery has power, your meter should show voltage resistance.

I think this is the answer. I hope this helps. :)
Hey Andy. Thank you for chiming in. I didn't realize that N1 was connected to N2. Looking at the diagrams in this post, I thought N1 post was isolated from N2-N8 of the Z fuse array. Do you know how exactly the N1 is connected to the N2? Is there some sort of relay that's not shown in those diagrams?





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Gee-pah

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Hey Andy. Thank you for chiming in. I didn't realize that N1 was connected to N2. Looking at the diagrams in this post, I thought N1 post was isolated from N2-N8 of the Z fuse array. Do you know how exactly the N1 is connected to the N2? Is there some sort of relay that's not shown in those diagrams?
Yes Dee. I believe there is some sort of relay that disconnects N1 from N2 in any of the following conditions on the 3.6L JL:

1) an instant at cold crank, where the ESS/Aux battery is isolated for a voltage check
2) ESS/Aux events

As it regards #1 there are some caveats. If you own a 3.6L JL produced in model years 2019 or later, OR you have a 2018 3.6L with the TSB 18-092-19 flash (available at your dealer,) if your ESS/Aux battery fails this pre-crank test, like all 3.6L JLs it will fail the first crank attempt, but subsequent ones will permanently disconnect N1 from N2 until the sooner of replacing/charging the ESS/Aux battery, and the cold crank that immediately follows your successfully addressing your ESS/Aux battery problems.

If you have a 2018 3.L JL without the flash, your vehicle won't crank barring workarounds like those Jerry @Jebiruph has been kind enough to share with us. :)
 

gm920

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Hey Andy. Thank you for chiming in. I didn't realize that N1 was connected to N2. Looking at the diagrams in this post, I thought N1 post was isolated from N2-N8 of the Z fuse array. Do you know how exactly the N1 is connected to the N2? Is there some sort of relay that's not shown in those diagrams?
The connection is through the PCR located in the back of the passenger wheel well behind the fender liner.
 
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Jebiruph

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Here's an updated diagram showing the aux neg and body gnd cable ends changing. The cable that used to just disconnect the aux battery neg from ground now disconnects both batteries from ground.

Here's the new cable configuration.
main positive cable change.PNG


For comparison, here's the old cable configuration.
main positive cable change b.PNG
 
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Jebiruph

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@demisx , repost any questions you still have after reviewing the new cable configuration and I'll try to answer any I can.
 

demisx

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The connection is through the PCR located in the back of the passenger wheel well behind the fender liner.
💡 A-a-h, I think I get it. The connection between N1 and N2 is via N1 -> PCR -> N3 -> N2. This is why I see a closed circuit when the Jeep is off. Thank you!

@demisx , repost any questions you still have after reviewing the new cable configuration and I'll try to answer any I can.
Thank you. You are very kind and your knowledge is highly appreciated. Your new diagram is exactly what I see going on in my 2021 JLUR 3.6L manual. I've already printed it and replaced the old one in my maintenance file. 👍
 

patternman

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Here's an updated diagram showing the aux neg and body gnd cable ends changing. The cable that used to just disconnect the aux battery neg from ground now disconnects both batteries from ground.

Here's the new cable configuration.
main positive cable change.PNG


For comparison, here's the old cable configuration.
main positive cable change b.PNG
I must be missing something here! the images look the same to me!
 

demisx

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Do you guys have any recommendation for the AUX battery load tester? Will this 100 amp one be too much for the

https://www.amazon.com/gp/product/B000F5HU6C
I must be missing something here! the images look the same to me!
Compare the two images side by side and look at the two black cables. You'll notice the difference. They are swapped in newer models.
 
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patternman

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TroyBoy

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How was a 30 amp fuse decided upon?
 

TroyBoy

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Originally, 30 was what people were using... Since 30.1+ can come into play, depending on the JL, probably prudent to use next size up 40. I know I run with a 40.
Thanks. I’m tempted to just yank the aux battery out and reroute the positive cable from the aux to the main.
 

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Gee-pah

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I'm concerned that some may be approaching this the wrong way. At risk of pointing on the obvious, wire gauge dictates fuse size more than fuse size is dictated by an owner's amperage needs in any particular situation.

And this is the case because fuses and circuit breakers, among other things, mostly are there to prevent wires from overheating and paired with the wires they protect.

Put another way, we size what we think could be the current between the two batteries and then go out and buy the right gauge wire for the task. We then fuse that wire with amperage fuses than are rated for that wire or are lower in amperage than that limit.

Jerry's @Jebiruph N1 -> N2, or if you prefer N1 -> main battery positive (same thing) hack, examined alone, was a terrific hack for the 2018 3.6JL . It got that model year's engine to cold crank even if the ESS/Aux battery lacked sufficient energy when tested by the vehicle just prior to the cold crank attempt. It fooled the vehicle into thinking that such tests were solely against the ESS/Aux battery when in fact, no other factory wiring changed, it put both batteries in parallel for not only that test, but all the time.

But that said, and in no way is this meant to be disparaging, just factual, once you successfully cold crank, (or while you're parked) the vehicle pairs N1 to N2 regardless of whether that jumper is there or not, only separating them for an instant at cold crank for the ESS battery test and for ESS events. And if you turn ESS off, then isolation is only for a second at cold crank.

So if N1 and N2 are connected by the PDC during all times but these two (cold cranks and ESS events) it would seem that concern over the fuse size might be overstated, particularly if you disable ESS--unless--which you should not do, your jumper has wire and fuse amperage that exceeds that of the high amp fuses 68368853AA .

Enter model years 2019 and beyond, or TSB 18-092-19 on 2018's and if that pre-crank test fails (without Jerry's hack,) the second crank that is attempted is solely against the main battery. If it succeeds the ESS off light is thrown to the dash and all subsequent cold cranks occur solely off the main battery the first time they're attempted, until the ESS battery is charged/replaced, or you reroute wiring to make the vehicle think this has happened, consistent with things Jerry has discussed here after this hack was introduced, as it relates to possibly running the batteries differently than the factory configuration has them set out to do.

I had this hack prior to getting TSB 18-092-19 on my 2018. Now it's stored in the cargo area. I never blew the 30 amp fuse it came with, nor tried a higher amperage fuse in it.

So a lot of what this hack had initial intention for when first introduced has been addressed by FCA, but Jerry has certainly integrated that jumper hack into more involved wiring schemes since then that allow the owner to operate the electrical system, with mere switch settings, to run as factory, or both batteries always connected, or just one battery (ESS or main) running the whole show. But again, most of time your 3.6L has N1 and N2 connected by the PDC.
 
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