Looking for proven jump start solution - My New JLUR 3.6L manual w/ESS cannot start under -15c

[Yann]

If you want to research this read below. I have a 3.6 manual with ESS and I personally did the ESS battery bypass myself. Like others have said this could also be a switch issue considering it is intermittent but this will remove the unknown of the ESS system for you. Hope it helps.

Jerry’s cheap and easy bypass of AUX:

https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

And his consolidated battery info thread:

https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-diagram.14401/

As my understand, fused jumper is to pretect overflow current to damage Aux battery connected equipment. In this case, jump start cable direct to N1 w/o this jumper should be safe, but using battery pack which generates big current in short time might need the fused jumper to protect those low current equipments? correct me if I am wrong.

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[Pismo61]

No. Just connect + cable to N1 and - to the main battery.

So,possitive to N-1 and negitive to main battery?

 

[Dyolfknip74]

Tt only happened under cold weather, cannot be loose cable ...

Never say "cannot" with anything electric. Cold weather 100% can affect something like a loose negative cable.

 

[GreySportySpice]

As my understand, fused jumper is to pretect overflow current to damage Aux battery connected equipment. In this case, jump start cable direct to N1 w/o this jumper should be safe, but using battery pack which generates big current in short time might need the fused jumper to protect those low current equipments? correct me if I am wrong.

I am slightly confused by your question. As I understand it the point of the jumper is to use the main battery to pull in the starter relay instead of relying on the aux battery. The fuse is not so much to protect any sensitive electronics as it is to protect you from pulling too much current through the wire. The jumper only makes the connection on startup when the computer is separating the 2 batteries. During 99% of operation the jumper is redundant.

I can not speak too much on how to jump start this setup however with the jumper installed I would attach the cables to the + and - of the main battery as ultimately that is where the cranking amps are coming from.

Edit: I have an 18' with no updates done. I did all of this a while ago so I think it would be wise to read up on the latest and greatest software updates as mentioned by @Tommywear

 

[Yann]

Yann:

I'm not sure I can answer your questions. I think though where I may be able to add value is to explain why some of the suggestions may have worked for others, and how you may have a similar or different setup.

@Jebiruph Jerry's forgotten more than I know. I'll cc him in case he needs to correct me.

@HiJinx69 Dan may have had success, where you might too, but for different reasons. You see, as on owner of a 2018, Dan may have a JL (I don't know, perhaps he does) that will not crank if the ESS battery is dead. This limitation was fixed with TSB 18-092-19 (perhaps he had this added at the dealer) such that subsequent attempts at cold cranking are attempted off the main battery while, if successful, the ESS battery is isolated out of the vehicle's electrical circuit until serviced.

This "trying the other battery" behavior is built into later 2018's and all model year 3.6L JLs thereafter.

Anyway, regardless of model year or transmission type (automatic or manual) it is my understanding that just prior to cold crank the 3.6L isolates the ESS battery to test it, and will not crank if its voltage is lacking. Putting a charger up to N1 (whose other end is the ESS battery's positive post) and the main battery negative terminal (which is directly connected by a cable to the ESS battery's negative terminal) may have allowed Dan's vehicle to see adequate voltage on the ESS battery to crank for Dan.

At rest, provided fuses in the PDC aren't blown or cables loose, both batteries are connected in parallel and such a step Dan describes should charge both batteries.

But unless your main battery was dead or not connected, or fuses were blown, or there's a problem with the rig best addressed by the dealer, I would think that your second crank attempt should have succeeded give your 2021 model year.

So what's a 2021 owner to do? I'd put your jumpers on the main battery as per factory. With a little patience, and as per the manual, this will charge both batteries while the vehicle is at rest given the parallel connection. But if you're running a portable power pack this may rob it of power to effect the crank.

So another school of thought is to try to crank shortly after connecting to the main battery. It may fail given lack of charge in the ESS battery, but try to crank again. This should switch to the main battery, which even if it's lacking in power has the jumpers attached to it.

This approach would not work for Dan if he has an old 2018 (like me) without TSB 18-092-19 (unlike me.)

Yann:

I'm not sure I can answer your questions. I think though where I may be able to add value is to explain why some of the suggestions may have worked for others, and how you may have a similar or different setup.

@Jebiruph Jerry's forgotten more than I know. I'll cc him in case he needs to correct me.

@HiJinx69 Dan may have had success, where you might too, but for different reasons. You see, as on owner of a 2018, Dan may have a JL (I don't know, perhaps he does) that will not crank if the ESS battery is dead. This limitation was fixed with TSB 18-092-19 (perhaps he had this added at the dealer) such that subsequent attempts at cold cranking are attempted off the main battery while, if successful, the ESS battery is isolated out of the vehicle's electrical circuit until serviced.

This "trying the other battery" behavior is built into later 2018's and all model year 3.6L JLs thereafter.

Anyway, regardless of model year or transmission type (automatic or manual) it is my understanding that just prior to cold crank the 3.6L isolates the ESS battery to test it, and will not crank if its voltage is lacking. Putting a charger up to N1 (whose other end is the ESS battery's positive post) and the main battery negative terminal (which is directly connected by a cable to the ESS battery's negative terminal) may have allowed Dan's vehicle to see adequate voltage on the ESS battery to crank for Dan.

At rest, provided fuses in the PDC aren't blown or cables loose, both batteries are connected in parallel and such a step Dan describes should charge both batteries.

But unless your main battery was dead or not connected, or fuses were blown, or there's a problem with the rig best addressed by the dealer, I would think that your second crank attempt should have succeeded give your 2021 model year.

So what's a 2021 owner to do? I'd put your jumpers on the main battery as per factory. With a little patience, and as per the manual, this will charge both batteries while the vehicle is at rest given the parallel connection. But if you're running a portable power pack this may rob it of power to effect the crank.

So another school of thought is to try to crank shortly after connecting to the main battery. It may fail given lack of charge in the ESS battery, but try to crank again. This should switch to the main battery, which even if it's lacking in power has the jumpers attached to it.

This approach would not work for Dan if he has an old 2018 (like me) without TSB 18-092-19 (unlike me.)

thanks for kindly detail explaining, seems not work for me neither even mine is 2021mode, let’s see what dealer will get

 

[Yann]

I am slightly confused by your question. As I understand it the point of the jumper is to use the main battery to pull in the starter relay instead of relying on the aux battery. The fuse is not so much to protect any sensitive electronics as it is to protect you from pulling too much current through the wire. The jumper only makes the connection on startup when the computer is separating the 2 batteries. During 99% of operation the jumper is redundant.

I can not speak too much on how to jump start this setup however with the jumper installed I would attach the cables to the + and - of the main battery as ultimately that is where the cranking amps are coming from.

Edit: I have an 18' with no updates done. I did all of this a while ago so I think it would be wise to read up on the latest and greatest software updates as mentioned by @Tommywear

Seems I misunderstood…

 

[Yann]

Never say "cannot" with anything electric. Cold weather 100% can affect something like a loose negative cable.

You’re right, nothing impossible, just don’t think that’ the root cause

 

[Yann]

I plan to try 2 things if happen again after dealer’s work, jump start to N1 & main negative to identify aux battery failure; try to start on 4L to identify “clutch position sensor” issue. Wish me lucky!

 

[HiJinx69]

So,possitive to N-1 and negitive to main battery?

Yes.

 

[Yann]

Dealer changed one of clutch switch and fix it, but I will buy a jump pack for emerg

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