3.6L ESS Dual Battery Consolidated Information

rbranst

New Member
First Name
Ryan
Joined
Apr 2, 2021
Messages
1
Reaction score
2
Location
Shawnee, Kansas
Vehicle(s)
2018 Jeep JL Rubicon
First - thanks to Jebiruph for this thorough thread. I can't see digging into an ESS issue without referring to this first. I wanted to pass my story along.
I encountered a dead battery and had to be jumped and thought it was a fluke. I got home and started the car back up just to make sure I was good. Next morning, battery was dead. I left the JL at home and drove another car. I picked up a brand new Optima DH6 on the way home from work that night and put it in. Car was still dead. It was at this point I began learning about the aux battery and realized I probably needed to replace that one too. Once I did this, the car would start again but it would never engage ESS and always gave me errors about either "Battery Charging" or "Battery Protection Mode". In the process of investigating all of this, I trickle charged for a day, but it made no difference. Aux battery voltage was fine, but main was 10.5-11 on the new Optima! I discovered the negative lead to the aux was corroded at the main battery Neg terminal. I cleaned it really good, trickle charged again and now my start stop worked briefly. Finally after a few days I began to suspect my main battery, it was always at 10.5V after long drives. I returned the Optima DH6 for a replacement. Once installed and the terminals lubricated everything works perfectly.
The overcomplicated system actually hid bad brand new battery! That's the one thing I would like everyone to get from this post. The Aux was definitely bad, but the bad main replacement I got really screwed up my troubleshooting. I was looking at alternator voltage, considering a battery sensor replacement, bad wiring harness, etc. Never considered a brand new Optima being bad!
 

ALRUI

Well-Known Member
First Name
Arnold
Joined
May 18, 2018
Messages
421
Reaction score
150
Location
Murphy, NC
Vehicle(s)
2018 JLU Sahara, 2003 F150 S-Crew FX4, Others
Never considered a brand new Optima being bad!
Bad Optima is horrible, I thought those were supposed to be awesome. Had it been sitting on the shelf for a long time?
 

Ghuddy

Member
First Name
Greg
Joined
Apr 7, 2021
Messages
8
Reaction score
2
Location
Knoxville
Vehicle(s)
Wrangler jl Sahara
Due to the quantity and length of ESS battery and electrical related threads, researching issues can be time consuming and confusing. I am using this post to make information and related links easily available. This first post will serve as a quick reference and I'll use the second post to provide more details.

JL Wranglers with the 3.6L ESS have 2 batteries, the Main battery that you see in the engine compartment and an Aux battery that is hidden underneath the Power Distribution Center. Each battery powers separate systems during an ESS auto stop. During normal operation, the batteries are connected together in parallel by the Power Control Relay.

JL Wranglers are jump-started just like any other vehicle, except with two batteries it will take more time/power.

On a properly operating system, the batteries are always connected in parallel through the PCR except during an ESS auto stop.

The batteries can go bad independently, but they will run down (or drain) together. Except when a bad battery relay (PCR) or or a blown PCR (ESS) fuse separates them, which will also prevent the Aux battery from charging.

My battery is dead and I can't jump start my jeep
On a properly functioning system the batteries go dead together, so to jump-start a JL you have to overcome two dead batteries. Compared to a single battery system, it will take more time/power to over come two dead batteries. Disconnecting the main battery and jump-starting with just the aux battery should be easier.

My dash is flashing on and off and I can't jump start my jeep
This condition seems to be caused when the Aux battery can provide some, but not adequate power to system electronics, either because it is bad or partially drained. A bad aux battery should be bypassed using a jumper or by unplugging the PCR. Partially drained means either both batteries are drained, or the aux battery is isolated (bad PCR or PCR fuse) and not getting charged. If only the aux is drained, bypassing it with a jumper or unplugging the PCR may be enough to get started, but a jump-start may still be needed. If both batteries are drained, a normal jump-start (more time/power) should be enough.

Bypassing the Aux Battery
A bad or discharged aux battery can affect PCR operation, which can be disruptive to system electronics and it may need to be bypassed. Bypassing can be accomplished by using a (fused) jumper wire to connect the main battery directly to the system electronics at PDC terminal N1 or by unplugging the PCR, preventing it from disrupting the system electronics.

Using the Aux Battery as a Dedicated Reserve Battery
A good aux battery can be bypassed and disconnected from the system (by removing the ground cable) to be held in reserve in case the main battery is not able to power a start. A dead main battery should be disconnected from the system before attempting to start from the reconnected aux battery. The aux battery should also be load tested and fully charged before relying on it as a dedicated reserve battery.

Links to Related ESS Information
(added descriptions to links 05/12/19)
3.6L ESS Battery Diagram
This thread started it all. Due to various conflicting information regarding the dual battery wiring, I made this basic diagram based on information available online.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-diagram.14401/

3.6L ESS Aux Battery Bypass
An Aux battery bypass lets you start/run with just the Main battery. Handy if the Aux battery is bad or you want to disconnect it to use as a reserve battery.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

3.6L ESS Battery Basics
Here is some basic electrical theory to explain the dual battery system and why it can be difficult to start with a portable battery booster.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-basics.20794/

3.6L ESS IBS Information
This thread provides information about the Intelligent Battery Sensor that monitors the health of the Main battery. It's this type of sensor that makes ESS systems possible by analyzing the ability of the battery to restart from an auto stop.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-ibs-information.22585/

3.6L ESS Battery Basic Load Testing (Battery Health Check)
If you're concerned about the condition of your batteries, here's how to check them with a cheap load tester.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-basic-load-testing.22031/

3.6L ESS Cold Start (added 4/26/19)
Why is the Aux battery so critical to the cold start process? (Critical, but unnecessarily so?)
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-cold-start.28297/
 

WranglerMan

Well-Known Member
First Name
Will
Joined
May 8, 2018
Messages
3,326
Reaction score
2,508
Location
Katy Texas
Vehicle(s)
2018 Wrangler JLU Sahara
Occupation
Gas Pipeliner
Vehicle Showcase
1
Bad Optima is horrible, I thought those were supposed to be awesome. Had it been sitting on the shelf for a long time?
Optima batteries have gone down hill over the years, not even close to the quality they used to be.....Better off with Odyssey, Northstar, Full River
 
OP
OP
Jebiruph

Jebiruph

Well-Known Member
First Name
Jerry
Joined
Feb 18, 2018
Messages
1,480
Reaction score
1,841
Location
Iowa
Vehicle(s)
2018 JLU, 2019 KL, 2020 JT
First - thanks to Jebiruph for this thorough thread. I can't see digging into an ESS issue without referring to this first. I wanted to pass my story along.
I encountered a dead battery and had to be jumped and thought it was a fluke. I got home and started the car back up just to make sure I was good. Next morning, battery was dead. I left the JL at home and drove another car. I picked up a brand new Optima DH6 on the way home from work that night and put it in. Car was still dead. It was at this point I began learning about the aux battery and realized I probably needed to replace that one too. Once I did this, the car would start again but it would never engage ESS and always gave me errors about either "Battery Charging" or "Battery Protection Mode". In the process of investigating all of this, I trickle charged for a day, but it made no difference. Aux battery voltage was fine, but main was 10.5-11 on the new Optima! I discovered the negative lead to the aux was corroded at the main battery Neg terminal. I cleaned it really good, trickle charged again and now my start stop worked briefly. Finally after a few days I began to suspect my main battery, it was always at 10.5V after long drives. I returned the Optima DH6 for a replacement. Once installed and the terminals lubricated everything works perfectly.
The overcomplicated system actually hid bad brand new battery! That's the one thing I would like everyone to get from this post. The Aux was definitely bad, but the bad main replacement I got really screwed up my troubleshooting. I was looking at alternator voltage, considering a battery sensor replacement, bad wiring harness, etc. Never considered a brand new Optima being bad!
Thanks for posting. I don't think the aux battery causes anywhere near the issues it gets credit for. After 3 years, my main needed replaced, but the aux is still good. It is part of an overly complicated system prone to failure, but it's usually not impossible to trouble shoot with the diagram and a volt meter. It's not like it's death wobble or something like that.
 

Mikeoso

Well-Known Member
First Name
Mike
Joined
Jul 6, 2019
Messages
2,539
Reaction score
19,391
Location
Iowa
Website
www.iowaparrotrescue.org
Vehicle(s)
Ram 1500, Jeep
Occupation
Retired history teacher
Forgive me if this is dumb, but...

My 2019 Sport with 3.6 (7000 miles on the clock...I 0nly drive it about once a week) has been reading "ESS Unavailable, Battery Charging" for at least 4 months. Vehicle always starts, even at -30 F, and main battery gauge reads 14.3 consistently. Dealership says bring it in overnight, warranty work. Rather not.

Given that I never use the ESS, do I really need to do anything? Is the aux maybe flat just because I dont drive enough?
 

WranglerMan

Well-Known Member
First Name
Will
Joined
May 8, 2018
Messages
3,326
Reaction score
2,508
Location
Katy Texas
Vehicle(s)
2018 Wrangler JLU Sahara
Occupation
Gas Pipeliner
Vehicle Showcase
1
Forgive me if this is dumb, but...

My 2019 Sport with 3.6 (7000 miles on the clock...I 0nly drive it about once a week) has been reading "ESS Unavailable, Battery Charging" for at least 4 months. Vehicle always starts, even at -30 F, and main battery gauge reads 14.3 consistently. Dealership says bring it in overnight, warranty work. Rather not.

Given that I never use the ESS, do I really need to do anything? Is the aux maybe flat just because I dont drive enough?
Could be a combination of not driving a lot and a bad battery, my suggestion is to get a smart charger of good quality like NOCO, CTEK or similar and charge it up and see if the issue gets resolved.
 

OldGuyNewJeep

Well-Known Member
Joined
Sep 21, 2017
Messages
3,177
Reaction score
5,244
Location
CT
Vehicle(s)
2018 Wrangler JL, 2016 Yukon XL
Forgive me if this is dumb, but...

My 2019 Sport with 3.6 (7000 miles on the clock...I 0nly drive it about once a week) has been reading "ESS Unavailable, Battery Charging" for at least 4 months. Vehicle always starts, even at -30 F, and main battery gauge reads 14.3 consistently. Dealership says bring it in overnight, warranty work. Rather not.

Given that I never use the ESS, do I really need to do anything? Is the aux maybe flat just because I dont drive enough?
That “gauge” is showing you how many volts the alternator is sending to charge the batteries, not how many volts the batteries have. The higher the number, the more depleted they are.

If you have a multimeter, disconnect the aux negative and test voltage of both main and aux, separately.

A quick easy test is to put Jeep in ACC mode and look at the voltage shown on EVIC. That is a more accurate picture of current voltage.

Lastly, but most importantly, buy a battery tender and use it weekly. Infrequent, short trips are a recipe for failure with this crappy dual battery setup.
 
OP
OP
Jebiruph

Jebiruph

Well-Known Member
First Name
Jerry
Joined
Feb 18, 2018
Messages
1,480
Reaction score
1,841
Location
Iowa
Vehicle(s)
2018 JLU, 2019 KL, 2020 JT
Updated post #1 with the following links

ESS Dual Battery Management (added 6/27/21)
This thread mainly discusses modifications needed to use the aux battery as an emergency spare. It also has some of the most current information on the ESS system in general.
https://www.jlwranglerforums.com/forum/threads/ess-dual-battery-management.60034/

3.6L ESS Bad Aux Battery No Start Firmware Fix (added 6/27/21)
Due to a firmware change, 2019 and newer JL cold starts are less reliant on the aux battery. There is a firmware update to implement this for the 2018 Jls.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-bad-aux-battery-no-start-firmware-fix.53608/
 

OldGuyNewJeep

Well-Known Member
Joined
Sep 21, 2017
Messages
3,177
Reaction score
5,244
Location
CT
Vehicle(s)
2018 Wrangler JL, 2016 Yukon XL
Using the Aux Battery as a Dedicated Reserve Battery
A good aux battery can be bypassed and disconnected from the system (by removing the ground cable) to be held in reserve in case the main battery is not able to power a start. A dead main battery should be disconnected from the system before attempting to start from the reconnected aux battery. The aux battery should also be load tested and fully charged before relying on it as a dedicated reserve battery.
Jerry, this question has likely been answered, but I can’t find it with so many pages…

With jumper in place and aux negative disconnected from the main battery, my multimeter shows continuity between that disconnected wire and the negative main battery post. Is that expected? (I stumbled upon this because I wanted to test that my cheap battery switch was actually doing its job.)
 
OP
OP
Jebiruph

Jebiruph

Well-Known Member
First Name
Jerry
Joined
Feb 18, 2018
Messages
1,480
Reaction score
1,841
Location
Iowa
Vehicle(s)
2018 JLU, 2019 KL, 2020 JT
Jerry, this question has likely been answered, but I can’t find it with so many pages…

With jumper in place and aux negative disconnected from the main battery, my multimeter shows continuity between that disconnected wire and the negative main battery post. Is that expected? (I stumbled upon this because I wanted to test that my cheap battery switch was actually doing its job.)
I've never measured for continuity across a battery before, so I had to check. The answer is yes. The path is aux battery negative through the aux battery and postive cable to N1, jumper to N2, battery cable to main battery positive and through the main battery to the negative.
 

OldGuyNewJeep

Well-Known Member
Joined
Sep 21, 2017
Messages
3,177
Reaction score
5,244
Location
CT
Vehicle(s)
2018 Wrangler JL, 2016 Yukon XL
I've never measured for continuity across a battery before, so I had to check. The answer is yes. The path is aux battery negative through the aux battery and postive cable to N1, jumper to N2, battery cable to main battery positive and through the main battery to the negative.
Thank you! The backstory is that I dismantled my bypass before having my dealer replace my radio and flash my PCM with recall Y07. After reassembling, I tested continuity through my battery switch. I thought that I’d done that when I originally setup, but now I’m thinking I did it just on the switch before hooking it up. It’s one of those cheap twist dial jobs.

Anyway, now I feel better. Thanks, again.
 

A10Cajun

Member
First Name
Danny
Joined
Apr 14, 2020
Messages
5
Reaction score
3
Location
Miami Beach
Vehicle(s)
2018 Wrangler JLU
Physical Appearance Diagram
(updated 10/14/19) (added PDF 10/13/19 - jumper diagram 2)

This diagram shows the physical locations of the cable connection and helps to understand what's being done in the photograph's that follow.
underhood jumper 3a.PNG


Jump Starting with a Battery Pack using just the Aux battery

(updated 04/16/2019)

With both batteries drained, disconnecting the main battery and jump-starting with just the aux battery should increase your chances of starting with a portable battery booster, as long as the Aux battery is a good battery (only drained). Disconnect the Main battery negative terminal and connect the booster to the Main battery positive and the disconnected negative terminal. This will boost just the Aux battery and not split the charge between both batteries. This is discussed later in this thread.

Here's the disconnected Main battery negative terminal.

charging aux.jpg


(updated 10/03/2019)
Depending on how depleted the Aux battery is, it may jump start quicker using a temporary jumper to provide power to PDC terminal N1 as shown in the picture. This effectively bypasses the pre-start Aux battery power test.
jumpstart aux boost.jpg



Aux Battery Bypass (PCR Bypass)
(updated 10/14/2019)

To accommodate the dual battery ESS system, the JL electronics have been separated into Aux powered systems and Main powered systems. The PCR (power control relay) is used to connect and disconnect the systems as needed. A bad or discharged aux battery can be disruptive to system electronics, especially during the starting procedure.

(4/26/19 An explanation of the cold start starting procedure is here https://www.jlwranglerforums.com/forum/threads/3-6l-ess-cold-start.28297/)

(updated 10/13/2019)
Using a jumper to bypass the PCR or unplugging it may restore the ability to start. For safety in case of an accidental short circuit, the jumper should have a fuse (30 amps worked for me). The jumper is installed between PDC terminals N1 (aux systems) and N2 (main systems) and directly connects the two systems, effectively bypassing the PCR. Unplugging the PCR (disabling it) keeps the main and aux systems always connected, but this will not work with a bad PCR or a blown PCR fuse.

ess bypass simple 4.PNG



Here's what using a jumper looks like, and it's discussed in this htread.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

bypass installed.jpg


(updated text and pics 10/10/19)
The PCR is located behind the front passenger side tire, and it is discussed in this thread.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-diagram.14401/ (See posts 75, 92, 93)
Unplugging the connector (red arrows) will disable the PCR, keeping the batteries connected full time.

pcr location b.jpg

pcr location 2b.jpg


Reading Individual Battery Voltage
(updated 04/13/2019)

Since the batteries are usually connected in parallel, following is how to electrically isolated them to check the individual battery voltage. Keep in mind that the best way to check the condition of a battery is load testing it, which is covered in this thread.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-basic-load-testing.22031/

There are two cables connected to the Main battery negative terminal, one is from the Aux battery negative terminal and the other is to the body ground. Disconnecting the Aux battery negative cable from the Main battery negative terminal will isolate the batteries to facilitate reading the voltage of the individual batteries.

Here's reading the aux battery voltage - Main positive terminal to Aux battery ground.
aux bat gnd.jpg



Here's reading the main battery voltage - Main positive terminal to Main battery ground.

main bat gnd.jpg
Jerry, Gentlemen et al,

I just want to say I REALLY APPRECIATE the time you have taken to provide this FREE information to us Jeep Lovers out there. I am new to my 2018 Jeep JL, and though I absolutely love the vehicle, I cannot STAND the ESS system! I love working on my own car, and with all the new electronics now a days, it makes it much more of a challenge than my 1974 VW beetle. :)

I am having a major headache with my JL and an ESS that is preventing the car from starting. But with all the information you have provided us, I am sure I will figure it out. Thank you again Jerry for taking the time to share, I will pay it forward when I can.

Cheers to all,
Danny
Due to the quantity and length of ESS battery and electrical related threads, researching issues can be time consuming and confusing. I am using this post to make information and related links easily available. This first post will serve as a quick reference and I'll use the second post to provide more details.

JL Wranglers with the 3.6L ESS have 2 batteries, the Main battery that you see in the engine compartment and an Aux battery that is hidden underneath the Power Distribution Center. Each battery powers separate systems during an ESS auto stop. During normal operation, the batteries are connected together in parallel by the Power Control Relay.

JL Wranglers are jump-started just like any other vehicle, except with two batteries it will take more time/power.

On a properly operating system, the batteries are always connected in parallel through the PCR except during an ESS auto stop.

The batteries can go bad independently, but they will run down (or drain) together. Except when a bad battery relay (PCR) or or a blown PCR (ESS) fuse separates them, which will also prevent the Aux battery from charging.

My battery is dead and I can't jump start my jeep
On a properly functioning system the batteries go dead together, so to jump-start a JL you have to overcome two dead batteries. Compared to a single battery system, it will take more time/power to over come two dead batteries. Disconnecting the main battery and jump-starting with just the aux battery should be easier.

My dash is flashing on and off and I can't jump start my jeep
This condition seems to be caused when the Aux battery can provide some, but not adequate power to system electronics, either because it is bad or partially drained. A bad aux battery should be bypassed using a jumper or by unplugging the PCR. Partially drained means either both batteries are drained, or the aux battery is isolated (bad PCR or PCR fuse) and not getting charged. If only the aux is drained, bypassing it with a jumper or unplugging the PCR may be enough to get started, but a jump-start may still be needed. If both batteries are drained, a normal jump-start (more time/power) should be enough.

Bypassing the Aux Battery
A bad or discharged aux battery can affect PCR operation, which can be disruptive to system electronics and it may need to be bypassed. Bypassing can be accomplished by using a (fused) jumper wire to connect the main battery directly to the system electronics at PDC terminal N1 or by unplugging the PCR, preventing it from disrupting the system electronics.

Using the Aux Battery as a Dedicated Reserve Battery
A good aux battery can be bypassed and disconnected from the system (by removing the ground cable) to be held in reserve in case the main battery is not able to power a start. A dead main battery should be disconnected from the system before attempting to start from the reconnected aux battery. The aux battery should also be load tested and fully charged before relying on it as a dedicated reserve battery.

Links to Related ESS Information
(added descriptions to links 05/12/19)

ESS Dual Battery Management (added 6/27/21)
This thread mainly discusses modifications needed to use the aux battery as an emergency spare. It also has some of the most current information on the ESS system in general.
https://www.jlwranglerforums.com/forum/threads/ess-dual-battery-management.60034/

3.6L ESS Battery Diagram
This thread started it all. Due to various conflicting information regarding the dual battery wiring, I made this basic diagram based on information available online.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-diagram.14401/

3.6L ESS Aux Battery Bypass
An Aux battery bypass lets you start/run with just the Main battery. Handy if the Aux battery is bad or you want to disconnect it to use as a reserve battery.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

3.6L ESS Bad Aux Battery No Start Firmware Fix (added 6/27/21)
Due to a firmware change, 2019 and newer JL cold starts are less reliant on the aux battery. There is a firmware update to implement this for the 2018 Jls.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-bad-aux-battery-no-start-firmware-fix.53608/

3.6L ESS Battery Basics
Here is some basic electrical theory to explain the dual battery system and why it can be difficult to start with a portable battery booster.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-basics.20794/

3.6L ESS IBS Information
This thread provides information about the Intelligent Battery Sensor that monitors the health of the Main battery. It's this type of sensor that makes ESS systems possible by analyzing the ability of the battery to restart from an auto stop.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-ibs-information.22585/

3.6L ESS Battery Basic Load Testing (Battery Health Check)
If you're concerned about the condition of your batteries, here's how to check them with a cheap load tester.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-basic-load-testing.22031/

3.6L ESS Cold Start (added 4/26/19)
Why is the Aux battery so critical to the cold start process? (Critical, but unnecessarily so?)
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-cold-start.28297/
Jerry, Gentlemen et al,

I just want to say I REALLY APPRECIATE the time you have taken to provide this FREE information to us Jeep Lovers out there. I am new to my 2018 Jeep JL, and though I absolutely love the vehicle, I cannot STAND the ESS system! I love working on my own car, and with all the new electronics now a days, it makes it much more of a challenge than my 1974 VW beetle. :)

I am having a major headache with my JL and an ESS that is preventing the car from starting. But with all the information you have provided us, I am sure I will figure it out. Thank you again Jerry for taking the time to share, I will pay it forward when I can.

Cheers to all,
Danny
 
Advertisement

Dwayne Lane's Chrysler Jeep Dodge
 
Advertisement
Top