Jumperless Aux Battery Bypass

[TX_Ovrlnd]

I finally did this mod after following it for months. BUT, now I have a problem:
After I removed fuse 42 and removed the aux ground, I started her up..
I got two dash errors...

Service Airbag System
Start/stop unavailable

I put everything back to original, and the Service Airbag System light stayed on, but shortly after restarts it went off and everything went back to original.

I still want to eliminate the ESS system battery, so how do I fix the problems?
Thanks!

Next time you try it, pull both battery cables and then just add the necessary one back. That should reset everything. You will lose radio presets.

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[joliett]

Next time you try it, pull both battery cables and then just add the necessary one back. That should reset everything. You will lose radio presets.

EXACTLY correct.... thank you TX_Ovrlnd.... I removed the connector to the battery neg terminal, which REMOVED BOTH GROUNDS TOGETHER, then from the connector,I removed the smallest gauge ground, and reinstalled just one main ground. Voila... It worked perfectly..
Thank you. So grateful..
.

 

[rcadden]

Yes. Pulling the fuse is what disables PCR, which is what controls ESS.

And, all you need to do is disconnect what should be the thinner of the 2 negative battery cables. Wrap the end with electrical or Tesa tape and zip tie out of the way.

OK, so my main battery died. Replaced tonight. $277 after core refund.

The aux battery replacement was $160. SmartStartStop is $130.

ESS doesn't really bother me, but if I can eliminate a limited-life-span battery *AND* save ~$30+, I'm in.

Reading all these threads is doing my head in, though. Here's my factory setup:

As you can see:

• Cable #1 is the thinner of the two. Cable #2 is the bigger.
• Cable #1 terminates with a bracket, which Cable #2 is currently attached to.
• Cable #1 is attached to the PCR (the little black box with the wiring harness plug) via a stud that presumably comes off/through the PCR.

So, if I'm reading everything correctly, I need to (in this order)

1. Pull Fuse 42
2. Remove Cable #2 from the bracket. Wrap it in a shop towel to temporarily isolate it
3. Remove Cable #1 from the PCR and wrap it in electrical tape or heatshrink to more permanently isolate it and zip tie it back out of the way.
4. Attach Cable #2 to the stud on the PCR
5. Profit?

With this setup, I have the following considerations:

1. There is still a rotting aux battery in my Jeep. At some point I'll want/need to remove this for my peace of mind. However, with the steps outlined above, the aux battery is completely isolated from the system and is not serving any purpose.
   1. It's not likely to be leaking fluid or anything (Jeep is a 2021 w/ 42K miles) but I still don't like the idea of an unused battery in there.
2. I can continue to drive around with no issues, but I should manually disable ESS whenever I drive. If I miss it once or twice, it's not the end of the world.
   1. If I buy a SmartStartStop, then I won't have to remember to push the button.

Am I missing anything? Did I get it all right?

 

[rcadden]

The cable that you wrap is the smaller diameter cable, yes, it's cable 2.

Then remove the larger diameter cable, and attach to the battery negative post.

Electrical tape up cable 2.

It's simple, and it works. Good luck amigo.

Can you confirm Cable #2 from my photo (which is the BIGGER cable in my setup)?

I thought I was needing to remove the SMALLER cable from the connection (Cable #1 in the photos above)?

 

[TX_Ovrlnd]

As you can see:

• Cable #1 is the thinner of the two. Cable #2 is the bigger.
• Cable #1 terminates with a bracket, which Cable #2 is currently attached to.
• Cable #1 is attached to the PCR (the little black box with the wiring harness plug) via a stud that presumably comes off/through the PCR.

So, if I'm reading everything correctly, I need to (in this order)

1. Pull Fuse 42
2. Remove Cable #2 from the bracket. Wrap it in a shop towel to temporarily isolate it
3. Remove Cable #1 from the PCR and wrap it in electrical tape or heatshrink to more permanently isolate it and zip tie it back out of the way.
4. Attach Cable #2 to the stud on the PCR
5. Profit?

With this setup, I have the following considerations:

1. There is still a rotting aux battery in my Jeep. At some point I'll want/need to remove this for my peace of mind. However, with the steps outlined above, the aux battery is completely isolated from the system and is not serving any purpose.
   1. It's not likely to be leaking fluid or anything (Jeep is a 2021 w/ 42K miles) but I still don't like the idea of an unused battery in there.
2. I can continue to drive around with no issues, but I should manually disable ESS whenever I drive. If I miss it once or twice, it's not the end of the world.
   1. If I buy a SmartStartStop, then I won't have to remember to push the button.

Am I missing anything? Did I get it all right?

Remove the fuse first before any cables!

My neg battery cables were reversed unfortunately (good going factory), so I have a very chunky wrapped cable thanks to the stud post.

Buy whichever ESS defeat device you want soon so you don't have to remember. Eventually you will want to address the useless mini battery, but that's for future you, screw that guy!

 

[jludave]

Can you confirm Cable #2 from my photo (which is the BIGGER cable in my setup)?

You need to remove and isolate cable #1. It should be the thinner of the 2 cables.

Pull fuse #42 first.

You should not have to remove cable #2 from the battery terminal.

I can continue to drive around with no issues, but I should manually disable ESS whenever I drive. If I miss it once or twice, it's not the end of the world.

Yes. Bypassing the aux battery does not disable ESS. If you don't push the button to disable, it will run off the main battery.

If I buy a SmartStartStop, then I won't have to remember to push the button.

Correct. You can also use a Tazer.

 

[Rhinebeck01]

Can you confirm Cable #2 from my photo (which is the BIGGER cable in my setup)?

I thought I was needing to remove the SMALLER cable from the connection (Cable #1 in the photos above)?

@rcadden

Aux battery negative cable, regardless of the model year JL will be the slightly smaller in diameter cable you find attached to the Main's negative terminal.

Remove Fuse F42 in the PDC first and then disconnect the Aux neg. cable.

There is no need to disconnect both cables at the Main's negative when you do the jumperless Aux battery bypass. (I have done this jumperless Aux battery bypass on quite a few JL's and JT's and never disconnected both cables..

On 2021 year model JL's -> Aux negative battery cable location change:
https://www.jlwranglerforums.com/forum/threads/ess-battery-cable-change.86624/

 

[rcadden]

You need to remove and isolate cable #1. It should be the thinner of the 2 cables.

Pull fuse #42 first.

You should not have to remove cable #2 from the battery terminal.

Except that in my photos, Cable #1 (smaller) terminates in a large connector to which Cable #2 is attached.

So I DO have to remove both - I need to remove Cable #1 (which will also remove Cable #2, since they are attached to each other), then detach Cable #2 from Cable #1, reattach Cable #2 to the battery and tape off Cable #1, right?

 

[joliett]

Except that in my photos, Cable #1 (smaller) terminates in a large connector to which Cable #2 is attached.

So I DO have to remove both - I need to remove Cable #1 (which will also remove Cable #2, since they are attached to each other), then detach Cable #2 from Cable #1, reattach Cable #2 to the battery and tape off Cable #1, right?

YES. Right.
Same as my 2021 Rubicon.

 

[jludave]

Except that in my photos, Cable #1 (smaller) terminates in a large connector to which Cable #2 is attached.

So I DO have to remove both - I need to remove Cable #1 (which will also remove Cable #2, since they are attached to each other), then detach Cable #2 from Cable #1, reattach Cable #2 to the battery and tape off Cable #1, right?

IDK why that seems to change from year to year. My 2020 was simply a matter of removing the skinnier of the 2 negative cables.

 

[TX_Ovrlnd]

IDK why that seems to change from year to year. My 2020 was simply a matter of removing the skinnier of the 2 negative cables.

It probably depends on who was working that part of the assembly process.?‍

 

[joliett]

It probably depends on who was working that part of the assembly process.?‍

It was because of engineering improvements. It was always the thinner cable to be removed.

 

[PGFDE121]

Just did this today as I was getting odd indicator lights on the dash. Auto stop eliminator should be in hand and plugged in tomorrow. Thanks all for sharing your knowledge, tips and tricks.

 

[steelponycowboy]

Exactly. The F42 fuse gives power to the PCR to get the signal from the computer to check the voltage on the aux battery only. By removing the fuse it just sees the main battery. Downside is you have to make sure you disable ESS or you will be starting the Jeep from a stop event with the main battery. Also remember if you have a bad aux battery it will drain off your main battery. Personal opinion I disconnected the aux negative for less of an issue to worry about.

So disconnect a negative cable at the main battery? Which one?

 

[Rhinebeck01]

So disconnect a negative cable at the main battery? Which one?

@steelponycowboy

You want to disconnect the Aux battery negative cable found on the negative side of the Main battery in the engine compartment. That particular black cable is always the slightly smaller diameter black cable of the 2 cables you find there.

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