3.6L ESS Aux Battery Bypass

[Gee-pah]

So to confirm,

you mean remove the negative cable with a 13mm nut going to the main batteries’ negative post, and then connect my tester to it and the other end of the tester to the untouched positive on the main?

the way I did it in the photo was I just completely disconnected the main battery and then performed the test as “in vehicle” with the two disconnected connectors.

I do! I can't remember if the nut is 13mm but yes. Restated it is the factory cable (1 of 2) CLOSER to the passenger's front quarter panel. The more distal cable on the main battery's negative terminal to the front passenger's quarter panel is, at its other end tied into the grounding point on the passenger's front quarter panel.

Maybe a narrative of why this works is indicated here.

Touch the tester to the positive terminal of the main battery will then provide the voltage to any circuit connected to that main battery terminal based on where you are about to place that negative tester terminal.

Were you to place the tester's negative side on the main battery's negative post, (and the cable discussed above is removed from the main battery's negative terminal) you'd get the main battery's voltage.

But if you were to put the negative side of the battery tester on the aforementioned dangling wire that you took off the main battery, which directly connects to the ESS/Aux battery's negative post, you would get the voltage of only the ESS/Aux battery.

If everything were hooked up as the factory provided the vehicle and you put your tester on the main battery terminals you would get a composite voltage of both batteries.

Testers read only complete circuits, agreed? Agreed.

Just such a circuit exists on the ESS/Aux battery, and only the ESS/Aux battery because there is a clean uninterrupted flow of electrons from the main battery's positive terminal (in the 3.6L JL) to

* terminal N2 in the Power Distribution Center (PDC),

* which is directly connected to neighboring N1 in the PDC at all times (including with the engine off and the rig parked) but an instant during an engine crank (on a 3.6L JL) and during ESS events....

(or hard connected to N1 at all times if you use Jerry's jumper......)

(Jerry's jumper can be between N1 and N2 or the main battery's positive terminal (which is hard wired to N2) and N1---it doesn't matter)

* and the cable off of N1 connects directly and uninterrupted to the positive terminal of the ESS/Aux battery,

* which connects internally in the ESS/Aux battery to the negative post of the ESS/Aux battery,

* which has a direct and uninterrupted cable coming off it to the main battery's negative post

* which you have disconnected from the main battery by design, preventing the main battery from being part of the circuit

* to which the negative prongs of your tester are attached...



Don't forget to reattach that cable back to the main battery's negative post when done with your testing.

Rob---if you have the time, this is an excellent read, where Jerry, who I learned much of this from, sets up a system where he can take voltages of neither, both, or just 1 of the 2 batteries by merely flipping some switches he includes in his setup. Some the very principles above apply.

https://www.jlwranglerforums.com/forum/threads/ess-dual-battery-management.60034/

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[RubiRob]

I do! I can't remember if the nut is 13mm but yes. Restated it is the factory cable (1 of 2) CLOSER to the passenger's front quarter panel. The more distal cable on the main battery's negative terminal to the front passenger's quarter panel is, at its other end tied into the grounding point on the passenger's front quarter panel.

Maybe a narrative of why this works is indicated here.

Touch the tester to the positive terminal of the main battery will then provide the voltage to any circuit connected to that main battery terminal based on where you are about to place that negative tester terminal.

Were you to place the tester's negative side on the main battery's negative post, (and the cable discussed above is removed from the main battery's negative terminal) you'd get the main battery's voltage.

But if you were to put the negative side of the battery tester on the aforementioned dangling wire that you took off the main battery, which directly connects to the ESS/Aux battery's negative post, you would get the voltage of only the ESS/Aux battery.

If everything were hooked up as the factory provided the vehicle and you put your tester on the main battery terminals you would get a composite voltage of both batteries.

Testers read only complete circuits, agreed? Agreed.

Just such a circuit exists on the ESS/Aux battery, and only the ESS/Aux battery because there is a clean uninterrupted flow of electrons from the main battery's positive terminal (in the 3.6L JL) to

* terminal N2 in the Power Distribution Center (PDC),

* which is directly connected to neighboring N1 in the PDC at all times (including with the engine off and the rig parked) but an instant during an engine crank (on a 3.6L JL) and during ESS events....

(or hard connected to N1 at all times if you use Jerry's jumper......)

(Jerry's jumper can be between N1 and N2 or the main battery's positive terminal (which is hard wired to N2) and N1---it doesn't matter)

* and the cable off of N1 connects directly and uninterrupted to the positive terminal of the ESS/Aux battery,

* which connects internally in the ESS/Aux battery to the negative post of the ESS/Aux battery,

* which has a direct and uninterrupted cable coming off it to the main battery's negative post

* which you have disconnected from the main battery by design, preventing the main battery from being part of the circuit

* to which the negative prongs of your tester are attached...



Don't forget to reattach that cable back to the main battery's negative post when done with your testing.

Rob---if you have the time, this is an excellent read, where Jerry, who I learned much of this from, sets up a system where he can take voltages of neither, both, or just 1 of the 2 batteries by merely flipping some switches he includes in his setup. Some the very principles above apply.

https://www.jlwranglerforums.com/forum/threads/ess-dual-battery-management.60034/

thank you for the amount of detail and information you provided. Wouldn’t I be getting the same reading by disconnecting the main battery from the two main cables and then testing the aux from those main cables?

 

[Gee-pah]

thank you for the amount of detail and information you provided. Wouldn’t I be getting the same reading by disconnecting the main battery from the two main cables and then testing the aux from those main cables?

Correct sir

 

[RubiRob]

So im running an optima yellow top as my main battery.

If I did a 10g inline fuse holder with 40a fuse, can I just disconnect my aux and run "everything as normal" but just with one battery? ESS and all?

 

[Gee-pah]

So im running an optima yellow top as my main battery.

If I did a 10g inline fuse holder with 40a fuse, can I just disconnect my aux and run "everything as normal" but just with one battery? ESS and all?

I'd say lower the gauge a bit (i.e. use thicker cable) at 40amps or down the amps to 30 for 10 gauge wire, or buy one of these:

https://www.amazon.com/gp/product/B000CZ2Z92/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Also--if you want to run one battery I'd recommend that you don't allow ESS to engage. The reason I say this is because ESS may remain on too long thinking the ESS battery (really now your main and only battery with the fused wiring) is chock full of current and that your main battery, which provides the majority of the current for post ESS event engine cranking, is sitting quietly behind the scenes ready to jump in and energize the engine crank, when in fact it is this main and only battery that is getting depleted during ESS events that may drop too low for a successful post ESS engine crank.

Then again it may not. But the 3.6L was designed and calibrated based upon two batteries. Sure, other vehicles run ESS with one battery but the thresholds for when an ESS event terminates because the voltage has dropped too low may be more aggressive in the 3.6JL than in other one battery ESS systems. The Wrangler may push limits with the two battery design that other one battery ESS vehicles don't.

 

[MacJack]

Jerry #Jebiruph I have to thank you for your work... You have given me great advise and direction... I made a jumper just in case of Aux battery goes dead. Since I may go weeks without driving my weekend drive with the Battery Tender which works great and not only keeping batteries up also puts them full charge and it over 2 year old JLR.

So I have been reading all the post and have to ask you and others after my warrenty is up should I be looking at other solutions... Has FCA come up with a better plan on other JL model years that I should get on my 2018 JLR. Has anyone updated the FCA.

I may not be asking the correct question(s) so let me say I have the extended warranty and want to keep that valid. Again do not know if I'm asking the correct question... Like if my Aux battery dies, just get another and keep Jerry jumper if it dies on the trail...

Thanks for your input in advance.

 

[OldGuyNewJeep]

So im running an optima yellow top as my main battery.

If I did a 10g inline fuse holder with 40a fuse, can I just disconnect my aux and run "everything as normal" but just with one battery? ESS and all?

I would not use ESS with one battery. Engineers put two in for a reason. If you are fine not using ESS, then go for it; I did.

I am using this inline 40a fuse. 10g is fine. Any thicker wire than that and you’re not going to get the fuse cover to close.

https://www.amazon.com/dp/B08JZ5C29C

 

[Gee-pah]

Jerry #Jebiruph I have to thank you for your work... You have given me great advise and direction... I made a jumper just in case of Aux battery goes dead. Since I may go weeks without driving my weekend drive with the Battery Tender which works great and not only keeping batteries up also puts them full charge and it over 2 year old JLR.

So I have been reading all the post and have to ask you and others after my warrenty is up should I be looking at other solutions... Has FCA come up with a better plan on other JL model years that I should get on my 2018 JLR. Has anyone updated the FCA.

I may not be asking the correct question(s) so let me say I have the extended warranty and want to keep that valid. Again do not know if I'm asking the correct question... Like if my Aux battery dies, just get another and keep Jerry jumper if it dies on the trail...

Thanks for your input in advance.

You asked (for) Jerry @Jebiruph. I've done so for you by preferencing his forum handle with an "at" sign as opposed to your use of a pound sign--no big deal.

That said, yes, I think FCA has come up with another, if not better plan on other 3.6L JL model years that you should consider getting on your 2018 3.6 JL.

Funny enough, Jerry first alerted me to it. It's PCM update is TSB 18-092-19, which seems to update the engine cranking logic on the 3.6L 2018 JL to behave like model years 2019 and beyond as described in the following:

In all 3.6L JL's, upon user request to cold crank the engine, the vehicle checks the ESS/Aux battery (or maybe I should say generically whatever the cables that lead to this battery out of the factory are connected to, in deference to Jerry's recent and more extensive hacks) for adequate voltage.

If it is lacking the vehicle won't cold crank. Never mind that if this battery did meet such power thresholds it would be connected in parallel to the main battery and the crank would be attempted, quite possible succeeding even if the ESS/Aux battery were shot, as the main battery provides most of the energy for this event. The fact is that in the 2018 3.6JL your main battery cables could be hooked up to a 12V utility power plant: a dead ESS/Aux battery equates with being stranded.

In fact, as you may know, that's where Jerry's jumper comes in, which never allows the ESS/Aux battery to be isolated, keeping the two batteries in parallel 100% of the time, as opposed to the 99.99% of the time from the factory but for an instant at engine crank and during ESS events.

The above flash changes this logic such that if the ESS/Aux battery fails this pre crank test the vehicle's engine crank logic switches to the main battery such that your initial attempt to crank may, yes, fail, but your subsequent attempts to crank may succeed, all while the "ESS disabled" diagnostic light is turned on in the dash until the ESS/Aux battery--or wherever its factory cables lead to, is replaced with a more powerful current source--usually a replacement ESS/Aux battery, and the default factory behavior of first checking the ESS/Aux battery is restored.

I can't for the life of me think why Jerry's hack should (famous last words I know) void the warranty. All it does it make the connection between the batteries parallel all the time.

But if you seek a FCA blessed method for better ESS/Aux battery fault tolerance, the aforementioned TSB is your play I think.

Perhaps Jerry has other thoughts.

 

[Jebiruph]

Jerry #Jebiruph I have to thank you for your work... You have given me great advise and direction... I made a jumper just in case of Aux battery goes dead. Since I may go weeks without driving my weekend drive with the Battery Tender which works great and not only keeping batteries up also puts them full charge and it over 2 year old JLR.

So I have been reading all the post and have to ask you and others after my warrenty is up should I be looking at other solutions... Has FCA come up with a better plan on other JL model years that I should get on my 2018 JLR. Has anyone updated the FCA.

I may not be asking the correct question(s) so let me say I have the extended warranty and want to keep that valid. Again do not know if I'm asking the correct question... Like if my Aux battery dies, just get another and keep Jerry jumper if it dies on the trail...

Thanks for your input in advance.

Here's my upgrade to the ESS system https://www.jlwranglerforums.com/forum/threads/ess-dual-battery-management.60034/ . It doesn't change much, just facilitates disconnecting the aux battery for use as an emergency spare and allows for monitoring the voltage of both batteries.

 

[Jebiruph]

I'd say lower the gauge a bit (i.e. use thicker cable) at 40amps or down the amps to 30 for 10 gauge wire, or buy one of these:

https://www.amazon.com/gp/product/B000CZ2Z92/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Also--if you want to run one battery I'd recommend that you don't allow ESS to engage. The reason I say this is because ESS may remain on too long thinking the ESS battery (really now your main and only battery with the fused wiring) is chock full of current and that your main battery, which provides the majority of the current for post ESS event engine cranking, is sitting quietly behind the scenes ready to jump in and energize the engine crank, when in fact it is this main and only battery that is getting depleted during ESS events that may drop too low for a successful post ESS engine crank.

Then again it may not. But the 3.6L was designed and calibrated based upon two batteries. Sure, other vehicles run ESS with one battery but the thresholds for when an ESS event terminates because the voltage has dropped too low may be more aggressive in the 3.6JL than in other one battery ESS systems. The Wrangler may push limits with the two battery design that other one battery ESS vehicles don't.

Don't you think the voltage of the main is monitored during an ESS stop and that the system will restart well before the main battery is too depleted, regardless of whether it is powering additional systems or not?

 

[Gee-pah]

Don't you think the voltage of the main is monitored during an ESS stop and that the system will restart well before the main battery is too depleted, regardless of whether it is powering additional systems or not?

I hear this Jerry, but we agree that the ESS/Aux battery, at least out of the factory, has its voltage monitored during ESS events....

or anything that ESS/Aux battery's cables have instead been connected to, like the main battery in one battery systems like the ones some of your hacks allow for.

Yes?

 

[RubiRob]

I would not use ESS with one battery. Engineers put two in for a reason. If you are fine not using ESS, then go for it; I did.

I am using this inline 40a fuse. 10g is fine. Any thicker wire than that and you’re not going to get the fuse cover to close.

https://www.amazon.com/dp/B08JZ5C29C

I just want to see if by isolating to main battery only, if that battery ever gets fully charged. Seems like unless im driving an hour a day every day they're always at 14.6 - 14.7 "charging." My battery tester said both are fine, but then again its a cheap amazon tester made in china.

 

[Gee-pah]

I just want to see if by isolating to main battery only, if that battery ever gets fully charged. Seems like unless im driving an hour a day every day they're always at 14.6 - 14.7 "charging." My battery tester said both are fine, but then again its a cheap amazon tester made in china.

Rob: a battery tester, particular a simple or cheap one as described, might be able to detect a bad battery, but such a tester's display of adequate results is by no means proof positive that the battery is heathy.

I suggest that you acquiring a load tester, or have someone with one conduct a test on your batteries. If you wish to save money I think Harbor Freight sells two different varieties, as sure as there are tons of them on the internet, and that many auto parts stores will conduct such tests for you for free.

 

[RubiRob]

Rob: a battery tester, particular a simple or cheap one as described, might be able to detect a bad battery, but such a tester's display of adequate results is by no means proof positive that the battery is heathy.

I suggest that you acquiring a load tester, or have someone with one conduct a test on your batteries. If you wish to save money I think Harbor Freight sells two different varieties, as sure as there are tons of them on the internet, and that many auto parts stores will conduct such tests for you for free.

Ya orielly will test it but they said their test requires me to remove it and then leave the battery on their tester for 1-1.5hrs. That’s fine but it would be nice to just do the bypass and be able to use my vehicle. And I figured it would show me if it’s my aux that’s taking forever to charge.

 

[Gee-pah]

Ya orielly will test it but they said their test requires me to remove it and then leave the battery on their tester for 1-1.5hrs. That’s fine but it would be nice to just do the bypass and be able to use my vehicle. And I figured it would show me if it’s my aux that’s taking forever to charge.

Ok...sorry for that. What I will say is that if you acquire your own tester, as you may already know, by no means need you gain access to the ESS/Aux battery to test it.

Simply remove from the main battery's negative terminal the factory cable CLOSER to the front passenger's fender. Stick your load tester's positive side on the positive of the main (yes, main) battery and the negative side of the tester on the negative cable that's dangle free that you just removed.

Make sure to put that cable back on the main terminal after the test.

BTW: a test of the main battery, while effected by simple connecting to its two terminals, ALSO requires this cable to be removed or else you'll be load testing the combined amp hours of the two batteries in parallel.

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