3.6L ESS Aux Battery Bypass

LooselyHeldPlans

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I admittedly didn’t read all 34 pages of this thread, but am I wondering about the thread specs of the wing nuts used to attach the bypass.

@Jebiruph, do you happen to know these specs? Might be a useful update to the original post.
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Apologies if this has been explained earlier in the thread ( I may have just missed it).

when viewing the voltage on the instrument cluster or through the 4x4 page, I assume when driving this is the alternator output and wondered when the rare occasions that the stop/start system actually operates and stops the engine, does this voltage display then show that of the main or auxiliary battery? I was thinking the latter but noticed that after the engine starts again, the voltage slowly increases back to 14v or whatever, making me then think that it perhaps only shows the voltage of the main battery, regardless.

Thanks in advance...
 
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Jebiruph

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Apologies if this has been explained earlier in the thread ( I may have just missed it).

when viewing the voltage on the instrument cluster or through the 4x4 page, I assume when driving this is the alternator output and wondered when the rare occasions that the stop/start system actually operates and stops the engine, does this voltage display then show that of the main or auxiliary battery? I was thinking the latter but noticed that after the engine starts again, the voltage slowly increases back to 14v or whatever, making me then think that it perhaps only shows the voltage of the main battery, regardless.

Thanks in advance...
I'm not sure which battery voltage is displayed during an auto stop. When I watched mine, there seemed to be a delay after the restart before the alternator voltage was displayed. That would indicate to me that it was monitoring the aux battery with the delay being from the battery relay reconnecting the aux battery.
 

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So can’t we follow this method of using the jumper terminals between N1 & N2 and wire a solenoid between the disconnected aux battery and ground, then use an aux switch inside the cab to toggle an auto jump start on and off plus reconnect charging to the aux battery whenever you feel necessary?
 
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Jebiruph

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So I had the Jeep not start on me a few days ago.. had the wife jump me and went along my way. Stumbled across this thread. I have a 2018 jl that hasn’t received the TSB as far as I know.

so my problem is when I disconnect aux ground to main battery and apply the jumper. The Jeep doesn’t start. Just hear clicking. If I reconnect the ground the Jeep starts fine. What am I doing wrong? I’ve attached pictures of someone could help.

the ground for the aux is on the same post as my winch and aux switch ground. I’ve added a red arrow to show the aux ground which I removed and taped with electrical tape.

5935FE16-F304-499D-989E-B3CDE0C6434A.jpeg


0BE653C3-E8FA-41AF-B0D0-91476E37F0A0.jpeg
 
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Jebiruph

Jebiruph

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So I had the Jeep not start on me a few days ago.. had the wife jump me and went along my way. Stumbled across this thread. I have a 2018 jl that hasn’t received the TSB as far as I know.

so my problem is when I disconnect aux ground to main battery and apply the jumper. The Jeep doesn’t start. Just hear clicking. If I reconnect the ground the Jeep starts fine. What am I doing wrong? I’ve attached pictures of someone could help.

the ground for the aux is on the same post as my winch and aux switch ground. I’ve added a red arrow to show the aux ground which I removed and taped with electrical tape.

5935FE16-F304-499D-989E-B3CDE0C6434A.jpeg


0BE653C3-E8FA-41AF-B0D0-91476E37F0A0.jpeg
It looks to me like your aux battery is the good battery and the main battery is the bad battery. Try leaving the aux connected and the main disconnected and see what happens.

You should probably get both batteries charged and load tested.
 

Gaxmode

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It looks to me like your aux battery is the good battery and the main battery is the bad battery. Try leaving the aux connected and the main disconnected and see what happens.

You should probably get both batteries charged and load tested.
Just to follow up. Replaced the main battery. Disconnected aux ground with jumper and everything started up fine. Thanks
 

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So to sum up 35 pages, can I just put a fuzed jumper between N1 and N2 and remove the aux negative from the main battery (taped with electric tape)and run it temporarily until my warranty appt in January?
 
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Jebiruph

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So to sum up 35 pages, can I just put a fuzed jumper between N1 and N2 and remove the aux negative from the main battery (taped with electric tape)and run it temporarily until my warranty appt in January?
You only need the jumper if you don't have the software update and can't start without it. If you have the software update, the jumper just keeps the ESS test from failing and turning on the error light. I wouldn't bother taping up the cable either, just bend it out of the way.
 

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You only need the jumper if you don't have the software update and can't start without it. If you have the software update, the jumper just keeps the ESS test from failing and turning on the error light. I wouldn't bother taping up the cable either, just bend it out of the way.
Thanks they updated the software last time the battery died. I was just trying to avoid the aux battery killing the main battery until I make it to the dealer. Still fighting with the idea of swapping it my self, but since it's still under warranty that idea really hurts.
 
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Jebiruph

Jebiruph

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Thanks they updated the software last time the battery died. I was just trying to avoid the aux battery killing the main battery until I make it to the dealer. Still fighting with the idea of swapping it my self, but since it's still under warranty that idea really hurts.
If you don't care if the error light is on, all you have to do is disconnect the aux ground cable. I was doing some ESS testing today and did this myself for a multi stop trip. The first start attempt will fail, every start after that will work as long as nothing else is wrong. Then shortly after starting the error light turns on.
 

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I've seen quite a few posts related to failed Aux batteries causing flaky or dead electronics, stalling and failing to start/auto restart. I've come up with a simple way to temporarily bypass a bad Aux battery (also blown PCR fuse or bad PCR) and get back on the road. Warning - this post contains a lot of informed assumptions, so post your related experiences to help validate or invalidate any information I've provided.

Here's a picture of my bypass kit. The jumper is used to connect the N1 terminal to the N2 terminal. I wanted to be able to install the jumper securely, but still be able to quickly disconnect it. A fused jumper seemed to be the best and cheapest way to go. Removing the fuse is a simple way to disconnect the jumper and it protects against overloading the wire. I don't know how much current will pass through the wire, so I used the largest I could find.

6/26/2021 Update - Many have reported that the 30A fused jumper shown in this picture has not been adequate for their JL. Use the highest capacity fused jumper you can find and make sure the fuse is not rated too high for the wire, otherwise the wire will melt before the fuse blows.
bypass kit 2.jpg


Here's how I tested the bypass. I disconnected the Aux battery at N1 and the ground wire at the Main battery negative terminal to simulate a bad aux battery. The voltmeter confirms the disconnect with low voltage at N1.
aux bat disconnected.jpg


Here's a shot of the dead instrument panel due to the disconnected Aux battery.
dash off.jpg


Here's the jumper installed between N1 and N2, voltmeter shows the Main battery voltage at N1.
bypass installed.jpg


Here's the live instrument panel.
dash on.jpg


Here's the instrument panel after starting, only error indicated is open hood.
dash running.jpg



For those interested, following are some diagrams to illustrate how I understand it works. (See this thread for additional information on the dual battery system https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-diagram.14401/)

Here's the battery voltages on a working system, the PCR is connecting the batteries in parallel, both batteries providing power to everything. Normal operation is verified with 0 volts between N1 and N2.
ess normal operation.PNG


Here's the effect of a failed Aux battery, no power to critical electronics. This should be verifiable by a voltage difference between N1 and N2.
ess bad aux.PNG


Bypassing is accomplished by jumping N1 to N2. This diagram illustrates the jumper getting power back to the critical electronics.
ess bypass.PNG



(updated 04/13/2019)
Additional 3.6L ESS system information is available here.
3.6L ESS Dual Battery Consolidated Information
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-dual-battery-consolidated-information.25377/
What size fuse would be best for the jumper if not 30amps
 
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