AUX battery delete/bypass - Which method is proper?

[Terry R]

I’m having the same warning light coming on after disconnecting the negative terminal and pulling fuse F42. But this was done when I installed a new H7 main battery. So battery shouldn’t be an issue. What else could be causing the warning?

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[PrimeTime4370]

I think 12.5 is a little low. Since the main battery is the starting battery, after a failed restart l would investigate the main battery. You may have eliminated the working battery.

I actually did not ave a failure to start on the first try after pulling the fuse and removing the ground. I will try resetting the IBS and report back.

 

[AndySpill]

I’m having the same warning light coming on after disconnecting the negative terminal and pulling fuse F42. But this was done when I installed a new H7 main battery. So battery shouldn’t be an issue. What else could be causing the warning?

I like what @andy29847 had to say above about this. https://www.jlwranglerforums.com/fo...ss-which-method-is-proper.123845/post-2589065

 

[Terry R]

I will try this and see what happens.

 

[Kleiss1]

I pulled the fuse and removed the auxiliary ground cable and start stop still working. Confused

 

[AndySpill]

I pulled the fuse and removed the auxiliary ground cable and start stop still working. Confused

You have taken the ESS battery out of the electrical schematic of the vehicle and tricked, by pulling the fuse, your JL into thinking that whenever it calls for isolated voltage tests of the ESS/Aux battery what it gets is a test of all connected batteries, which is just for you the main battery.

None of this starts up or shuts down the independent ESS system, whose only commonality with the ESS battery is the term ESS.

To shut down the ESS system press the button or buy tech to do it for you.

Clearer?

 

[PrimeTime4370]

Rest IBS. Same result. Still have warning light and message in cluster. New H7 battery it is I suppose.

 

[Jaon]

Because you disconnected the ESS/Aux battery doesn't mean, before you did so, or by the mere passage of time, your main battery isn't also in need of service.

The steps you took now make calls by your vehicle to read only the ESS/Aux battery's voltage read all available batteries' voltage, which in your case is only the main battery. And if that battery is need of replacement, no differently than an ESS/Aux battery on its "last legs," you could have the message you describe.

Of course it could be something else but if it were me I'd load test the main battery.

Good luck finding cause.

My main battery only had 300 CCA left. It was very tired

 

[bobholthaus]

Bob:

I thought I covered this, but even if I did, I completely get that I may have not gotten this message conveyed. (I can only imagine the things I read where I don't glean 100% of the writer's intent.) Let me try this in another way.

It's really this simple.

There are no error lights because your JL is unaware that Fuse 42 is not in place, and that the Power Control Relay (PCR), that device that separates the batteries for an instant at cold crank and during ESS events, can't function because of this fuse pull.

Your JL aimlessly thinks it is isolating the ESS/Aux battery for testing, when pulling Fuse 42 prevents that, and instead, calls for electrical current from this ESS/Aux battery are instead routed to both batteries: which for you is only the main battery, because you have disconnected the ESS/Aux battery.

It is precisely because this method of removing the ESS/Aux battery from the electrical schematic is so silent, that it is recommended to turn off the ESS system, or risk it engaging from solely the main battery.

Here again, many vehicles run ESS from one battery. But to repeat, the perfect storm of a cold night, long traffic light, old main battery, and (aftermarket) appliances could find you sucking voltage from your main battery, which will early terminate the ESS event, hopefully in time for the main battery to still have adequate cranking power to restart the engine that charges it.

We can only guess what threshold levels the engineers at Stellantis set this early ESS event termination level at, and whether they were more aggressive with it than vehicles running ESS with only one battery (and most other vehicles aren't nearly as often outfitted with as many energy sucking aftermarket appliances), precisely because, as designed from the factory, the main battery is preserved during ESS events in the dual AGM battery JL, to effect the bulk of the work in the post ESS event crank., unlike in other vehicles.

Shane from Genesis Offroad knows a thing or two about the JLs energy consumption and from what I've read is fine running ESS events off the main battery, but it's also true, given the way Stellantis designed the ESS system, ESS will stop working after 6 ESS events under one engine crank, resetting itself at the next cold crank, if the vehicle sees identical voltages between (what it thinks) are the ESS and main battery, assuming there must be some electrical short between the two batteries that cause it to read a voltage this is a composite of both batteries linked in parallel (like what you see on the dash in accessory mode with the engine off with two factory batteries connected.)

Because Shane runs ESS events off the main, absolutely no disparaging intent implied, he faces this 6 ESS event test.

I've never run that many, (6) ESS events under one cold crank. It is an awesome kit for overlanders and I only mention this 6 ESS event condition to highlight when, and when not, your JL is aware of the changes you are making.

All this said, there is another route. You could disconnect your ESS battery and stop, no fuse pull, no N1 to N2 jumper, Jerry's original technique.

Doing so will prevent an early model 2018 without software upgrade from cranking. Dual AGM battery JLs in later model years will fail on the first crank attempt but subsequent ones will succeed provided the main battery has ample power, turning ESS off in the dash. In this case you not pulling Fuse 42 or jumpering N1 to N2 DID make the JL aware that something was wrong.

And some may call this approach, if you don't mind idiot lights in the dash, a good thing. You don't need to remember to turn ESS off with the button or buy tech to do it.

But, as raised by me in a prior thread about this, Jerry believes the ESS off light in the dash serves as an early warning sign of problems, that if you expressly engage, might cause you to miss out on knowing of problems with your vehicle, and he doesn't advise it.

Thank you for this re-explanation. This is the one that clarified it for me. I appreciate it.

 

[bobholthaus]

By turning off the ESS system, but leaving all else connected, you are risking the ESS/Aux battery, with time, being the more likely of the two batteries to start to cannibalize the main battery. You see both batteries are connected in parallel (positive to positive, negative to negative) at all times but an instant at cold crank and during ESS events.

For those already committed to not running ESS there is little upside to keeping the ESS/Aux battery connected in my opinion. If you must find an upside, when that ESS/Aux battery is working well, it aids the main battery in cranking the engine.

I'm going to make a medical analogy. This is serious. A young mom presents to her obstetrician/gynecologist with known genetics for breast cancer but is hell bent on breast feeding her infants (running ESS.) We let her do so, with 6 month mamograms (we trickle charge the batteries and load test them.)

Over time, as the kids age, their nutrition comes from food not breast milk. When that now older mom visits the obstetrician we have a conversation about getting her into a oncological breast surgeon to have a radical bilateral prophylactic (that's what it's called folks) mastectomy (removal of the breast tissue) (disconnecting the ESS battery and fuse pull) followed, while still anesthetized , a plastic surgeon performing breast reconstructive surgery to make her whole again.

Those "girls," like your ESS battery that isn't routinely trickle charged, are, IMHO, time bombs. If you are not running the ESS system (breast feeding), there's little upside to holding on to such a precancerous entity: literally or metaphorically.

Funny, but helpful explanation.

Thank you everyone for your input on this thread. It’s all hugely appreciated.

 

[bobholthaus]

It's hard to have a discussion about battery subjects without Jerry's diagram.

Andy: where do I find my N3 fuse? I wonder if I blew this when I was messing around trying to find a reverse tap for my SwitchPros system.

After reading your chart, I wonder if my Aux battery is dead because I blew that fuse. I was using a Tazer to bypass ESS but one day the dash lit up, ignition locked, and the jeep was towed to the dealership. I never put the taser back in (because I thought IT caused all of this), and my ESS has been disabled ever since (which would make sense, as maybe that was the day my aux battery actually died). I was blaming the disabled ESS on the taser, when I now see I should have been blaming it on the dead Aux battery. Ironically, I’ve been happy that the ESS hasn’t been working, but now I see that a dead Aux battery will likely lead to a dead main battery! (Hence the questions here). I think I’ll have the dealer replace the Aux batt. under warranty, and test my main battery (and maybe replace it under warranty), and then I’ll do this mod.

@Rhinebeck01 tagging you here

 

[bobholthaus]

@AndySpill now can you explain, in your most basic terms, what I do with the cables if I decide to remove the entire Aux battery (which I may also do). 2023 JL Diesel, so not worried about 2018 model issues. Thanks.

 

[andy29847]

Andy: where do I find my N3 fuse? I wonder if I blew this when I was messing around trying to find a reverse tap for my SwitchPros system.

After reading your chart, I wonder if my Aux battery is dead because I blew that fuse. I was using a Tazer to bypass ESS but one day the dash lit up, ignition locked, and the jeep was towed to the dealership. I never put the taser back in (because I thought IT caused all of this), and my ESS has been disabled ever since (which would make sense, as maybe that was the day my aux battery actually died). I was blaming the disabled ESS on the taser, when I now see I should have been blaming it on the dead Aux battery. Ironically, I’ve been happy that the ESS hasn’t been working, but now I see that a dead Aux battery will likely lead to a dead main battery! (Hence the questions here). I think I’ll have the dealer replace the Aux batt. under warranty, and test my main battery (and maybe replace it under warranty), and then I’ll do this mod.

@Rhinebeck01 tagging you here

Fuses shown around the 4 minute mark.

 

[THAW]

I actually did not ave a failure to start on the first try after pulling the fuse...

The start fail occurs only if you don't pull the fuse.

 

[THAW]

where do I find my N3 fuse?

The fuse is part of the PDC bus. It's underneath the N3 post.

If the N3 fuse is blown the aux battery powers system electronics but doesn't receive a charge from the alternator. In short order, you'd have bigger problems than an ESS warning.

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