Jumperless Aux Battery Bypass

[JL MADDOG]

@Fudster

Elliot,

Thanks for the info. I wondered about that as I read the OP's instructions. Nothing was said about having any error messages when the battery connection and F42 were removed.

There is something else at play here. I have the "Smart Stop Start" module installed in the OEM harness which allows for ESS to be off each time I start the vehicle.

In that condition, with the aux battery cable connected to the battery and F42 installed, the ESS On/Off light on the OEM button is lit but no messages come up in EVIC.

I wanted to avoid any aux battery issues with it in the electrical system.

Maybe I should put the cable back on the battery and re-install F42?

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[Planotex]

I just bluetooth to my phone and jump my battery. Drains your phone fast...

 

[OldGuyNewJeep]

@Fudster

Elliot,

Thanks for the info. I wondered about that as I read the OP's instructions. Nothing was said about having any error messages when the battery connection and F42 were removed.

There is something else at play here. I have the "Smart Stop Start" module installed in the OEM harness which allows for ESS to be off each time I start the vehicle.

In that condition, with the aux battery cable connected to the battery and F42 installed, the ESS On/Off light on the OEM button is lit but no messages come up in EVIC.

I wanted to avoid any aux battery issues with it in the electrical system.

Maybe I should put the cable back on the battery and re-install F42?

SSS and/or Tazer are fine. (I have both, and currently running with the Tazer.)

You should not have any error messages. Something else is at play. I’d start by charging your main battery with a *good* charger (must be 10a or better for the main battery).

 

[mdkautzman]

Can it be certain models or years that get error messages? See it reported a lot on here.
My 2020 JT Sport Base worked great. I'm leary of what my 2021 JL Sport S will do now that I read some of the posts.

Anyone collecting data on year or model?

 

[Fudster]

@Fudster

Elliot,

Thanks for the info. I wondered about that as I read the OP's instructions. Nothing was said about having any error messages when the battery connection and F42 were removed.

There is something else at play here. I have the "Smart Stop Start" module installed in the OEM harness which allows for ESS to be off each time I start the vehicle.

In that condition, with the aux battery cable connected to the battery and F42 installed, the ESS On/Off light on the OEM button is lit but no messages come up in EVIC.

I wanted to avoid any aux battery issues with it in the electrical system.

Maybe I should put the cable back on the battery and re-install F42?

Hey Michael:

Let's talk about the effect "Smart Stop Start" should have here on the cold crank, where I'm with @OldGuyNewJeep: there is none. Whether the device is present or absent, engaged or not, dual AGM battery JLs crank using the same algorithm.

So let's divert our attention to the difference between Fuse 42 intact and the ESS battery connected (factory conditions,) versus the fuse pulled as well as the cable off the main battery's negative terminal whose distal end is connected to the negative terminal of the ESS battery.

At pre-crank your factory wired dual AGM battery JL is going to go through the motions of energizing a relay to isolate the two batteries and test only the ESS battery, Smart Stop Start present or not, engaged or not, unless even if your ESS battery (or what your vehicle thinks is your ESS battery) is dead can't crank the engine.

That's a mouthful. So let's run some scenarios.

In your case, as you described, with the factory wiring, it is going to find that battery to not only have enough current to continue with the crank--where thereafter both batteries are reconnected in parallel and both energize the crank, but enough energy in the ESS battery to not turn on the ESS off light in the EVIC.

Often owners' ESS batteries have adequate power to continue with the crank but not enough to keep the ESS light from illuminating in the EVIC.

Then there's owners with factory wiring and dead ESS batteries. For those, the initial crank attempt fails. Subsequent attempts to crank though, (provided you have a dual AGM battery JL of model year 2019 or greater, or a 2018 with TSB 18-092-19, i.e. you) go only against the main battery, and if successful, turn on the ESS off light in the EVIC and keep it illuminated forever more until the next cold crank, if any, when an energized ESS battery is connected. All future cranks, until an energized ESS battery (or something else****) is found on the factory cables will occur on the first attempt against only the main battery. But the vehicle will still attempt to isolate the batteries at cold crank time hoping to find an energized ESS battery (or what it thinks is one based on your Fuse 42 pull and the main battery now being swapped in as what your JL thinks is the ESS battery during the pre-crank.)

Now, let's talk about your setup, the "something else" here. You both a) removed your ESS battery from the vehicle's electrical schematic when you took the cable whose distal end is connected to the negative terminal of the ESS battery off the negative terminal of the main battery, as well as b) removed the ability for the vehicle to isolate the ESS battery, even if it were connected, with the Fuse 42 removal. No longer are we dealing with factory wiring: which is fine and neither good nor bad.

At crank the vehicle attempts (Smart Start Stop or not, engaged or not) to energize the relay to separate the batteries but fails silently, unknown to any vehicle diagnostic, because of the fuse 42 pull. The vehicle then proceeds with what it thinks is the ESS battery test, thinking its isolated that ESS battery (even though it not only hasn't, but that battery is disconnected in your case), and in actuality, because it can't isolate the batteries, does the ESS battery test on all available batteries, which for you is only the main battery.

Your rig thinks your main battery is your ESS battery and sees it as having enough power to continue with the crank, but not enough to allow ESS to engage, turning the ESS off light on in the EVIC.

Charge that main battery Michael and let us know what you find. If the ESS off light continues to go on perhaps the main battery needs to be replaced, or perhaps, if fully charged, some other aspect of the vehicle is causing that ESS off light to illuminate.

I base my findings on your prior detail of when the ESS off light illuminates and doesn't.

 

[RangerRobAZ]

Thanks to OP for figuring this out and everyone who confirmed it worked for them. Really nice to not worry about the AUX battery causing me issues.

I removed the fuse and disconnected the negative wire going to AUX battery. Been running without issues for a couple weeks so far, no error lights. 2020 JLUR.

Edit - now running for 2 years without any issues.

 

[Betttty White]

Wow. This is great info

 

[FrostQ]

Thank you all for the information!!!!
I just did the F42 pull and negative disconnect...and my ESS light lit up on the dash. Perhaps my ESS battery was draining the main for a while, because it's only showing 12.3V on the dash. Going to try to charge it up as per suggestions by Fudster above and see what happens. Maybe I'll need to replace this 2020 battery sooner than I thought.

 

[jludave]

I just pulled the F42 fuse and disconnected my aux negative cable. Performed several starts without issue nor any lights on the dash. Also did a quick remote start, also with zero issues. I haven't gone on a drive yet, but don't expect any issue when I do.

Many thanks to @Jebiruph and @Rhinebeck01 for the invaluable info in this thread. Next goal is to replace my main battery which is just over 3 years old.

 

[Wrangler man]

I just pulled the F42 fuse and disconnected my aux negative cable. Performed several starts without issue nor any lights on the dash. Also did a quick remote start, also with zero issues. I haven't gone on a drive yet, but don't expect any issue when I do.

Many thanks to @Jebiruph and @Rhinebeck01 for the invaluable info in this thread. Next goal is to replace my main battery which is just over 3 years old.

Tried the above with zero success and the stop start still triggered strangely not as often before I pulled 42 and disconnected the cable. I would get that new battery sooner than later because you will not be able to jump start your dead battery once it dies. That's why I did the permanent complete fix and completely removed the auxiliary battery.

 

[jludave]

Tried the above with zero success and the stop start still triggered strangely not as often before I pulled 42 and disconnected the cable.

You do know that even with the AUX battery bypass, ESS still works? It just works off the main battery if you don't manually turn it off via the button or have a device (Tazer, etc.)to do it for you.

 

[STW]

fwiw, two months running now on only the (damaged) main stock H6 battery, and the jumperless aux battery bypass works fine.

No ESS messages so the main must stay sufficiently charged-- I keep the damaged Main battery charged with a maintainer nightly.

ESS still works fine with only the Main battery--but I use ESS rarely and only when I forget to push the dash button. But anytime ESS does operate, it seems fine. Usually I remember to push the button.

I said "damaged" main, because my stock main battery got damaged being over-discharged through the cannibalistic ESS system before I figured out it was happening (with help from posters here--thanks). It's still showing low cranking voltage (9.5v or less) on about half the starts, so I need to replace that. Considering removing the Aux battery too, just because it bugs me to have it in there. The only reason to keep it in for me is it returns to stock quicker for a dealer visit and may prevent a dealer claiming whatever is wrong is because I disconnected the Aux battery. Maybe I'm too paranoid.

Keep in mind that the ESS/Aux battery system is about powering accessories during long stops, and you can judge how draining your accessories are. Let's assume the Jeep computer is pulling more power than the minimal computer in my old TJ use to pull--that's something that is drawing power during an ESS event. Then lights, heater or AC operations (or does AC turn off during an ESS stop?), stereo/radio. That's my list, as far as I can tell. Some people will have heated seats on and I imagine that's a much larger drain on the battery during an ESS event.

 

[Rhinebeck01]

Tried the above with zero success and the stop start still triggered strangely not as often before I pulled 42 and disconnected the cable. I would get that new battery sooner than later because you will not be able to jump start your dead battery once it dies. That's why I did the permanent complete fix and completely removed the auxiliary battery.

You are incorrect... You can jump start when the Aux is just bypassed. You do not need to delete the Aux battery as you say.

I have been running with Main bypassed for well over 4 yrs.. Aux is still in place.

 

[Wrangler man]

You do know that even with the AUX battery bypass, ESS still works? It just works off the main battery if you don't manually turn it off via the button or have a device (Tazer, etc.)to do it for you.
[/QUOT that is correct it could just be my imagination but it seems far less than when I had the auxiliary battery and the crap shoot of the two batteries fighting against each other just seem never ending. The voltage used to jump all over the place now it remains consistent.
Q. I'm searching for a low budget non-Taser fix to disable this and do tire size correction anyone have suggestions of a tried and true platform? I run the Banks Derringer pedal monster now and hesitate adding more if it's even possible.

 

[Fudster]

@Wrangler man

Hey Howard:

When you wrote that bypassing the ESS battery will not allow you to charge the main battery when it dies, my"read" was that a dead battery won't charge well, not that the ESS bypass somehow prevents the jump starting of the remaining battery.

Is that correct?

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