Jumperless Aux Battery Bypass

[Fudster]

Hey all, pulled the fuse and the terminal and I still have the avengers symbol on the dash (ess error). I had the ess error before I pulled the fuse (which prompted my investigation into a bad aux battery - I had just replaced the main). Do I have to do something to clear the ess error?

Do you have TSB 18-092-19? If you did, what I think should have happened is the next cold crank after you pulled Fuse 42 the vehicle would have attempted to isolate the ESS/Aux battery cables for an instant at cold crank, to test what's at the end of those ESS/Aux cables,(nothing) but would have failed at that isolation of the ESS/Aux battery because the normally closed relay that separates the batteries for an instant prior to cold crank and during ESS events, can't be energized to open, to separate the batteroes without Fuse 42 in place, and those calls to the ESS/Aux battery would have just been routed to the main battery.

The vehicle would think this was the ESS/Aux battery, seen an energized battery and turned the ESS off light off.

That's what I think might happen if you have TSB 18-092-19. I haven't tried it, I could be wrong or it could be something else, but given that some 2018's don't have the TSB, I'd look there first.

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[PatrickR]

Do you have TSB 18-092-19? If you did, what I think should have happened is the next cold crank after you pulled Fuse 42 the vehicle would have attempted to isolate the ESS/Aux battery cables for an instant at cold crank, to test what's at the end of those ESS/Aux cables,(nothing) but would have failed at that isolation of the ESS/Aux battery because the normally closed relay that separates the batteries for an instant prior to cold crank and during ESS events, can't be energized to open, to separate the batteroes without Fuse 42 in place, and those calls to the ESS/Aux battery would have just been routed to the main battery.

The vehicle would think this was the ESS/Aux battery, seen an energized battery and turned the ESS off light off.

That's what I think might happen if you have TSB 18-092-19. I haven't tried it, I could be wrong or it could be something else, but given that some 2018's don't have the TSB, I'd look there first.

I'm going to check if I have that TSB. If I recall, if the ess is not connected and the fuse installed, the jeep won't start without the update from that TSB? That might be the easiest way to check...

 

[Fudster]

I have a mid-year 2018 3.6 and just performed this "mod" today. I have the TSB 18-092-19 update that was applied back when it first became available. The Aux battery has been a real landmine for me in the past and has led to a fair amount of heartburn as I use my Jeep in the AZ backcountry fairly often.

Bit of recent backstory -
I recently forgot to turn off my GMRS radio and left the Jeep sitting for about 8-9 days. I was able to start the Jeep, but it really had to pull deep to get it going.

I pulled the F42 fuse and then disconnected the Aux ground. Jeep tried to start, but failed - as expected.

"As expected..." are you saying this because your batteries were dead and you thus didn't expect to turn over, or because you expected the first crank attempt with the ESS/Aux battery disconnected to fail.

If the second point , your assumption may be wrong. This failure behavior is expected if you have Fuse (42) is still connected.

A dual AGM JL with a dead ESS/Aux battery and Fuse 42 still connected, or a JL with two dead batteries exhibits the initial crank attempt behavior you describe.

You pulling that fuse put all the wires that from the factory lead to the two batteries in a permanent state of parallel. The ESS/Aux battery, even if still connected, couldn't be isolated.

However, on the 2nd attempt it wouldn't turn over

Ryan: if connected, at rest your two batteries are in parallel and I suspect the GMRS radio, accordingly, caused both batteries to lose power.

I wouldn't expect any model year dual AGM battery Wrangler to crank here. Not on first attempt, not on 75th attempt, Fuse 42 connected or pulled.

- Man battery was toast, reading 9.8v.

It sounds like both batteries were connected when the GMRS radio was energized. Both batteries were toast. It's just that hooked together in parallel they provided lightly greater amp hour power than one battery

When the Aux was previously connected it would at least grunt and turn over, so I'm assuming it was in parallel at the time and giving the main some guts to get her going.

Correct sir.

Jumped the Jeep with F42/Aux still disconnected and used my NOCO for the boost.

And that NOCO charged the main battery as well, if connected at the time, the ESS/Aux. I'm not sure in the time line if you disconnected the ESS/Aux battery before applying the NOCO.

Hit up Autozone today and installed a new Duralast Platinum AGM H7 Group 94R. Jeep fires right up. No errors or issues across about a dozen starts today.

As we'd hope, sounds good.


I'll keep you guys posted if I run into any issues. I'm running the Bradshaw Trail this weekend in Southern California desert, so we'll be out in the cold for a few nights and using some accessories.

Massive thanks to @Jebiruph @Rhinebeck01 and everyone that has contributed to this thread and all of the other countless pages of battery knowledge on the forums. The Aux battery is truly an unwarranted PITA for all of us. If you're ever in North Phoenix, I'll buy you a beer! ?
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[Fudster]

I'm going to check if I have that TSB. If I recall, if the ess is not connected and the fuse installed, the jeep won't start without the update from that TSB? That might be the easiest way to check...

Hey Patrick. It's easiest if I wrote the logic and steps in narrative form.


You press the crank button with the brake depressed. If it can your rig will isolate the ESS/Aux battery and test it. It can't do that if Fuse 42 is pulled. If that test fails, and you have the TSB, and your main battery has ample power, the next crank should succeed, where the vehicle will take the ESS/Aux battery out of the schematic, illuminate the ESS off light and crank/run only off the main battery, on the first attempt thereafter, until the crank after, if at all, an energized ESS/Aux battery is introduced.

If you don't have the TSB your main battery could have enough power to get a nuclear sub's reactor going, the rig won't crank if the ESS/Aux battery is dead or disconnected and Fuse 42 is intact. I think that that's how you think you last left the rig.

If Fuse 42 is pulled, the pre crank isolation of the ESS/Aux battery can't happen. Provided whatever battery or batteries you have connected pass the pre crank test, the vehicle will attempt to crank.

 

[PatrickR]

Hey Patrick. It's easiest if I wrote the logic and steps in narrative form.


You press the crank button with the brake depressed. If it can your rig will isolate the ESS/Aux battery and test it. It can't do that if Fuse 42 is pulled. If that test fails, and you have the TSB, and your main battery has ample power, the next crank should succeed, where the vehicle will take the ESS/Aux battery out of the schematic, illuminate the ESS off light and crank/run only off the main battery, on the first attempt thereafter, until the crank after, if at all, an energized ESS/Aux battery is introduced.

If you don't have the TSB your main battery could have enough power to get a nuclear sub's reactor going, the rig won't crank if the ESS/Aux battery is dead or disconnected and Fuse 42 is intact. I think that that's how you think you last left the rig.

If Fuse 42 is pulled, the pre crank isolation of the ESS/Aux battery can't happen. Provided whatever battery or batteries you have connected pass the pre crank test, the vehicle will attempt to crank.

So I'm going to reinstall fuse 42 and see if it fails to crank. If it doesn't turn over, that would mean I don't have the tsb completed.

Any chance you know if a pre-tsb jl will throw a light with ess disconnected and fuse 42 pulled? I guess I'm still unsure why it's throwing the light if all the jeep can see is the one (good) battery....

 

[Fudster]

So I'm going to reinstall fuse 42 and see if it fails to crank. If it doesn't turn over, that would mean I don't have the tsb completed.

Provided you have the ESS/Aux battery connected, and it lacks adequate charge, and Fuse 42 is connect, and the rig fails to crank no matter how much you try, yes this would suggest the absence of the TSB or a dead main battery as well, or both.

Any chance you know if a pre-tsb jl will throw a light with ess disconnected and fuse 42 pulled? I guess I'm still unsure why it's throwing the light if all the jeep can see is the one (good) battery....

I don't. With Fuse 42 pulled, no dual AGM battery JL, the aforementioned TSB installed or not, can isolate the ESS/Aux battery to know its dead, and should the TSB be installed, attempt to crank on the second attempt against the main battery, and if successful, turn the ESS off light on.

What can happen though is that if the main battery is also dead, and you have this TSB, and Fuse 42 is pulled, the Wrangler may think that it tested the ESS/Aux battery when really it tested whatever battery or batteries were connected.

Then, if a good main battery is introduced, provided you have the TSB, the JL may think on subsequent crank attemtps that it's isolated the ESS/Aux battery out of the electrical schematic, as per the TSB, which it can't do because Fuse 42 is yanked (and the relay that separates the two batteries can't be energized ,) and then when it cranks with the new main battery, throw this ESS light up.

But then on a subsequent cold cranks, provided the TSB is there, the rig will attempt to test the ESS/Aux battery alone for power. It will fail doing so given Fuse 42 is pulled. It should find what it thinks is an energized ESS/Aux battery, even though there's no ESS/Aux battery there, because isolation of the ESS/Aux battery is impossible with Fuse 42 pulled and calls for testing the ESS/Aux battery for current are made to the main battery (as well because Fuse 42 is pulled.)

Provided the TSB is installed and the main battery has power, the vehicle should crank, thinking it found a worrking ESS/Aux battery, and turn the ESS off light off. The power the rig found was though in a working main battery.

This is all confusing I know!

 

[PatrickR]

Ok, this is still bugging me, since no matter the configuration, the jeep should only be seeing one (good) battery.

Once the "service ESS" error is tripped, does it need a code reader or otherwise in order for it to reset?

Thanks for all the help on this btw, this forum is awesome!

 

[4x4tographer]

Thanks for the response man!

"As expected..." are you saying this because your batteries were dead and you thus didn't expect to turn over, or because you expected the first crank attempt with the ESS/Aux battery disconnected to fail.

If the second point , your assumption may be wrong. This failure behavior is expected if you have Fuse (42) is still connected.

A dual AGM JL with a dead ESS/Aux battery and Fuse 42 still connected, or a JL with two dead batteries exhibits the initial crank attempt behavior you describe.

You pulling that fuse put all the wires that from the factory lead to the two batteries in a permanent state of parallel. The ESS/Aux battery, even if still connected, couldn't be isolated.

I had already removed F42 and disconnected the Aux ground. I expected the first attempt to crank to fail - which it did.

I provided a timeline below for some additional clarity around how this all went down.

It sounds like both batteries were connected when the GMRS radio was energized. Both batteries were toast. It's just that hooked together in parallel they provided lightly greater amp hour power than one battery

I agree.

And that NOCO charged the main battery as well, if connected at the time, the ESS/Aux. I'm not sure in the time line if you disconnected the ESS/Aux battery before applying the NOCO.

In terms of timeline:

1. Jeep struggled to start, but would start due to the batteries being in parallel, as you noted
2. I removed F42 and disconnected the Aux ground
3. Jeep would not start. It attempted to, but failed.
4. I tried to start it a 2nd time, per the procedure for the jumperless bypass. Jeep failed to start the 2nd time. Attempted to, but failed (again).
5. Measured main battery and found low 9.8v
6. NOCO jump pack got it started
7. Installed new battery (I never reconnected F42 or the Aux ground)
8. Jeep fires up perfectly (F42 and Aux ground are still disconnected)

My assumption is the procedure was a success, despite the dead battery issue.

I use a Taser JL with the ESS kill feature enabled.

 

[Kleiss1]

I just disconnected my 2021 JLURD. Display showed start/stop not working because battery charging.
Removed fuse and cable and it still says same thing. Charging 13+.

 

[PegFundy]

Hi everyone. Hoping for some quick help here. The battery died on my early 2018 JLU yesterday & I purchased & installed a new main. I purchased a new aux but haven't installed it yet because I wanted to order replacements for the fender clips I'm sure I will break when I remove the fender. Those should come in the mail next week. In the meantime I leave at 6am tomorrow for 5 hours of driving. Is there a quick workaround to get me through a few days until my fender clips arrive in the mail without killing my new main? Do I just pull that fuse outlined in the original post, find the attachment point of the aux to the main and tape it off for now? Sorry there are over 100 posts & replies about this on the forum - I'll spend all day reading them and run out of daylight to go do this today, just trying to FF to the best workaround in the next 4 hours.

 

[azwjowner]

Hi everyone. Hoping for some quick help here. The battery died on my early 2018 JLU yesterday & I purchased & installed a new main. I purchased a new aux but haven't installed it yet because I wanted to order replacements for the fender clips I'm sure I will break when I remove the fender. Those should come in the mail next week. In the meantime I leave at 6am tomorrow for 5 hours of driving. Is there a quick workaround to get me through a few days until my fender clips arrive in the mail without killing my new main? Do I just pull that fuse outlined in the original post, find the attachment point of the aux to the main and tape it off for now? Sorry there are over 100 posts & replies about this on the forum - I'll spend all day reading them and run out of daylight to go do this today, just trying to FF to the best workaround in the next 4 hours.

Just remove and tape off the aux cable and ignore the error message. No need to even pull the fuse. You can always disconnect the battery later to clear the message.

 

[PegFundy]

Just remove and tape off the aux cable and ignore the error message. No need to even pull the fuse. You can always disconnect the battery later to clear the message.

Thank you! I'll also make sure to turn off ESS every time I start it until I get the new aux installed.

 

[Jebiruph]

I just disconnected my 2021 JLURD. Display showed start/stop not working because battery charging.
Removed fuse and cable and it still says same thing. Charging 13+.

The battery charging message refers to the main battery not the aux battery. Removing the fuse and cable won't affect the state of charge of the main battery.

 

[PegFundy]

I did it! It started! It seems normal! I ended up taking out the fuse too. So if I just return the aux battery & fender clips and use that money on a tazer I can just leave the dead aux in place forget ESS and move on with a much simpler situation?

 

[azwjowner]

I did it! It started! It seems normal! I ended up taking out the fuse too. So if I just return the aux battery & fender clips and use that money on a tazer I can just leave the dead aux in place forget ESS and move on with a much simpler situation?

Correct. Just make sure the disconnected aux cable is taped up real good so it can't short to anything. By pulling the fuse, you prevented seeing the error message. You can operate like that indefinitely.

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