Aux Battery issue

Martin1128

Member
First Name
Martin
Joined
Jan 11, 2020
Messages
12
Reaction score
3
Location
Houston
Vehicle(s)
2018 wrangler Sahara
Just replaced the main battery about a month ago now I'm getting a warning on the dash that says auto start stop not available. I'm guessing the aux battery is bad but does this power anything else? Cause I'm kind of liking not having the ESS system on. Would it be bad to not replace the aux battery? It still starts up fine without it.
Advertisement

 

Gee-pah

Banned
Banned
First Name
Andy
Joined
Nov 19, 2019
Messages
1,659
Reaction score
1,240
Location
SanFrancisco
Vehicle(s)
JL Wrangler
Just replaced the main battery about a month ago now I'm getting a warning on the dash that says auto start stop not available. I'm guessing the aux battery is bad but does this power anything else? Cause I'm kind of liking not having the ESS system on. Would it be bad to not replace the aux battery? It still starts up fine without it.
Ok. How do I condense pages on this?

This is a 2018 and a 3.6L JL correct?

If so, both batteries are hooked up in parallel 99.9% of the time but for a second during a cold crank, and during ESS events, the latter of which you report that you are not currently experiencing because the rig is telling you that the system isn't ready.

During a cold crank request (on 2018 3.6JLs at least, or so it's been tested), just prior, the Aux battery is isolated for an instant and tested. If it lacks sufficient current the JL won't attempt a crank, even if the main battery, which BTW bares the brunt of the crank load, has more than sufficient power to turn over the engine.

If the AUX battery has sufficient power to turn over the rig, even if not enough to run ESS events once the rig is warmed up, both batteries are reconnected in parallel just prior to the crank.

I might put a trickle charger on the main battery if you can when parked. This will charge both batteries because, as said, in the 3.6L these batteries are in parallel at rest.

It sounds like your ESS battery should be taken to the dealer and tested by them in isolation. Also, are you known to take more frequent shorter trips? Have you started and used the vehicle less during COVID?

It seems this start logic may be different from newer 3.6L models in that a dead AUX battery won't leave you unable to crank, as tested and reported in the forum. I have no idea if this newer logic was downloaded to 2018 JLs.

This crank logic, which I've always said makes no sense, seems to have been cloned from what happens during ESS events, where the voltage in the ESS battery is far less of an issue because if it drops too low, the ESS event automatically is ended before the brake pedal is released, to get the engine started to power the alternator to refresh the batteries.
 
OP
OP

Martin1128

Member
First Name
Martin
Joined
Jan 11, 2020
Messages
12
Reaction score
3
Location
Houston
Vehicle(s)
2018 wrangler Sahara
It's my daily and driven a lot. 2018 and already has 65k miles so it's not like its sitting there. I saw some other post saying the vehicle wont start if the aux battery is bad but so far it's still starting. I really hate the ESS especially since I live in Houston and we need ac. When everything was working i would turn off the ESS by pressing the button. But now it just has the warning at startup which I dont really mind but wasnt sure if I could be causing any other issues by leaving it this way.
 

Jebiruph

Well-Known Member
First Name
Jerry
Joined
Feb 18, 2018
Messages
1,483
Reaction score
1,846
Location
Iowa
Vehicle(s)
2018 JLU, 2019 KL, 2020 JT
It's my daily and driven a lot. 2018 and already has 65k miles so it's not like its sitting there. I saw some other post saying the vehicle wont start if the aux battery is bad but so far it's still starting. I really hate the ESS especially since I live in Houston and we need ac. When everything was working i would turn off the ESS by pressing the button. But now it just has the warning at startup which I dont really mind but wasnt sure if I could be causing any other issues by leaving it this way.
JLs with updated firmware will start with a bad aux, including 2018s. With the newer firmware, once a bad aux is detected, it seems like the error will stay until cleared.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-bad-aux-battery-no-start-firmware-fix.53608/

You can leave it as is, but if the aux is really bad, it could be damaging your main battery and it should be disconnected. Lots of information in this thread, including how to disconnect the aux battery. https://www.jlwranglerforums.com/forum/threads/3-6l-ess-dual-battery-consolidated-information.25377/

My advice would be to resolve any issues with the aux battery, then run with it disconnected.
You will still have the error with stop/start disabled, but you will have a good aux battery as a backup if needed.
 

Yellow Cake Kid

Well-Known Member
Joined
Nov 20, 2019
Messages
703
Reaction score
361
Location
USA
Vehicle(s)
Surly ECR
I would be concerned that the Aux battery will slowly impact the fortitude of the primary battery. If the auxiliary battery is connected in parallel with the primary battery most of the time, which it is, and it is undercharged, it will quietly suck energy from the primary battery as the array seeks equilibrium.

A parallel circuit with one good battery and one bad battery will try to become two mediocre batteries, and then things will get worse from there.

oops ... I should have read the whole thread ... the answer has already been provided :)
 
OP
OP

Martin1128

Member
First Name
Martin
Joined
Jan 11, 2020
Messages
12
Reaction score
3
Location
Houston
Vehicle(s)
2018 wrangler Sahara
Thanks guys. Probably going to replace the aux and just bypass it.
 

Gee-pah

Banned
Banned
First Name
Andy
Joined
Nov 19, 2019
Messages
1,659
Reaction score
1,240
Location
SanFrancisco
Vehicle(s)
JL Wrangler
JLs with updated firmware will start with a bad aux, including 2018s. With the newer firmware, once a bad aux is detected, it seems like the error will stay until cleared.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-bad-aux-battery-no-start-firmware-fix.53608/

You can leave it as is, but if the aux is really bad, it could be damaging your main battery and it should be disconnected. Lots of information in this thread, including how to disconnect the aux battery. https://www.jlwranglerforums.com/forum/threads/3-6l-ess-dual-battery-consolidated-information.25377/

My advice would be to resolve any issues with the aux battery, then run with it disconnected.
You will still have the error with stop/start disabled, but you will have a good aux battery as a backup if needed.
Hey Jerry. Thanks for this. I've read the links included and may have missed this but is the firmware update you describe one that all 2018 3.6L JLs get or need it be requested, or say, is it automatically the product of a VIN being (recently) flashed at the dealer?

Is there a way for me to confirm I have it, or to implement it myself? What language might I use with a dealer to request it the next time I'm there, say, for a routine oil change? I read your supplied ticket from the dealer about the radio flashing that was in your supplied link. The dealer writeup seemed sparse as to this cold crank logic change....maybe I missed it.

Thanks.
 

Gee-pah

Banned
Banned
First Name
Andy
Joined
Nov 19, 2019
Messages
1,659
Reaction score
1,240
Location
SanFrancisco
Vehicle(s)
JL Wrangler
I would be concerned that the Aux battery will slowly impact the fortitude of the primary battery. If the auxiliary battery is connected in parallel with the primary battery most of the time, which it is, and it is undercharged, it will quietly suck energy from the primary battery as the array seeks equilibrium.

A parallel circuit with one good battery and one bad battery will try to become two mediocre batteries, and then things will get worse from there.

oops ... I should have read the whole thread ... the answer has already been provided :)
Not only do I agree, but the only critique I might offer is that you're being...."too kind."

Put two beakers of water next to each other with different heights of water and connect those two beakers near the bottom and those beakers will in short order adjust their water volumes so each has their water at the same height. Evidence suggests that the Egyptians knew about this (water levels--still used today) to make two distal build sights of Pyramids built centuries ago at the same height.

No different in principle is hooking up two batteries of approximate common voltage in parallel (positive to positive, negative to negative) with no regulation in between. In short order--maybe not as quick as the water example, those voltages will approach the same level: the stronger battery attempting to charge the weaker. As mentioned, a 3.6L JL at rest has its batteries connected in parallel.
 

Jebiruph

Well-Known Member
First Name
Jerry
Joined
Feb 18, 2018
Messages
1,483
Reaction score
1,846
Location
Iowa
Vehicle(s)
2018 JLU, 2019 KL, 2020 JT
Hey Jerry. Thanks for this. I've read the links included and may have missed this but is the firmware update you describe one that all 2018 3.6L JLs get or need it be requested, or say, is it automatically the product of a VIN being (recently) flashed at the dealer?

Is there a way for me to confirm I have it, or to implement it myself? What language might I use with a dealer to request it the next time I'm there, say, for a routine oil change? I read your supplied ticket from the dealer about the radio flashing that was in your supplied link. The dealer writeup seemed sparse as to this cold crank logic change....maybe I missed it.

Thanks.
I don't have information related to the scope of the update, but I assume it is for all 2018 JLs. It wouldn't have been applied to my JL if I hadn't requested the radio upgrade.

With my sport and 5" radio, I never found a way to display my firmware version and I've never heard of a way for the owner to do the update. The 7" and 8.4" radios maybe different.

I wasn't aware that the PCM upgrade fixed the "bad aux - no start issue" until I tested mine. Knowing that now, the verbiage I would use with the dealer to request the update is "I want the firmware update installed that fixes the bad aux - no start issue". They won't know what you're talking about, so you'll need to the number of the update. I think it would be hard for them to deny an update with such serious implications.
 

WranglerMan

Well-Known Member
First Name
Will
Joined
May 8, 2018
Messages
3,327
Reaction score
2,509
Location
Katy Texas
Vehicle(s)
2018 Wrangler JLU Sahara
Occupation
Gas Pipeliner
Vehicle Showcase
1
I will wait for my aux to die then jumper N1/N2 and disconnect the ESS negative and run with one battery, currently my 2018 JL has 35k miles on it and I trickle charge both batteries together once a month, I leave the charger connected for a few days and so far so good but I carry the jumper and have wingnuts holding the jumper and ESS negative on but have the fuse pulled from the jumper
 

Rhinebeck01

Well-Known Member
Joined
May 9, 2018
Messages
8,021
Reaction score
10,243
Location
.
Vehicle(s)
2018 2dr. Rubi
I will wait for my aux to die then jumper N1/N2 and disconnect the ESS negative and run with one battery, currently my 2018 JL has 35k miles on it and I trickle charge both batteries together once a month, I leave the charger connected for a few days and so far so good but I carry the jumper and have wingnuts holding the jumper and ESS negative on but have the fuse pulled from the jumper
Personally, I think it is more prudent to take the Aux out of the picture before it dies... out of the picture so it cannot have a negative impact on the Main battery ever. Even though out of the picture, I still think it is paramount to maintain the Aux battery... at the least, it is a backup for the Main battery. To each his own.... 8-)
 

Gee-pah

Banned
Banned
First Name
Andy
Joined
Nov 19, 2019
Messages
1,659
Reaction score
1,240
Location
SanFrancisco
Vehicle(s)
JL Wrangler
I will wait for my aux to die then jumper N1/N2 and disconnect the ESS negative and run with one battery, currently my 2018 JL has 35k miles on it and I trickle charge both batteries together once a month, I leave the charger connected for a few days and so far so good but I carry the jumper and have wingnuts holding the jumper and ESS negative on but have the fuse pulled from the jumper
Maybe already known or said, but maybe don't run ESS with one battery if the rig otherwise lets you.

Jumpering N1 and N2 probably means that tests of ESS battery voltage during an ESS event are really tests of the main battery.

Connected as per factory, the ESS design is such that should the ESS battery drop voltage too much during an ESS event, the event ends prematurely for the spared main battery to bare the brunt of the engine crank to get the alternator back in the "battery charging business."

Under the jumper approach your depleting the very main battery during an ESS event that may inspire the premature ending of the ESS event for that very depleted main battery to attempt the crank.
 

WranglerMan

Well-Known Member
First Name
Will
Joined
May 8, 2018
Messages
3,327
Reaction score
2,509
Location
Katy Texas
Vehicle(s)
2018 Wrangler JLU Sahara
Occupation
Gas Pipeliner
Vehicle Showcase
1
Personally, I think it is more prudent to take the Aux out of the picture before it dies... out of the picture so it cannot have a negative impact on the Main battery ever. Even though out of the picture, I still think it is paramount to maintain the Aux battery... at the least, it is a backup for the Main battery. To each his own.... 8-)
Bill,

I may try your method but so far I have had zero issues but maybe i have been lucky, I don’t use ESS and have it bypassed with my SSS module but I do trickle charge once a month on both batteries and have checked both with my meter and voltages on both are above 12.6 at rest

Maybe already known or said, but maybe don't run ESS with one battery if the rig otherwise lets you.

Jumpering N1 and N2 probably means that tests of ESS battery voltage during an ESS event are really tests of the main battery.

Connected as per factory, the ESS design is such that should the ESS battery drop voltage too much during an ESS event, the event ends prematurely for the spared main battery to bare the brunt of the engine crank to get the alternator back in the "battery charging business."

Under the jumper approach your depleting the very main battery during an ESS event that may inspire the premature ending of the ESS event for that very depleted main battery to attempt the crank.
I have ESS disabled with a SSS module and never use it but do randomly engage it to see if I get any messages and so far it has always displayed ready and I have no error messages displayed in the EVIC, heck I have even recently tested the actual shut down and start of the ESS operation and it works as designed but I don’t do this often.

I had my main battery replaced 7 months after I got my JL in 2017 as it failed but both batteries are almost 3 years old and doing ok but like I said I have been trickle charging for a long time so maybe that has kept both healthy
 
Advertisement

Icon Vehicle Dynamics
 
Advertisement
Top