Jebiruph
Well-Known Member
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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/
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/
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