Remove Auxiliary Battery

[jav_eee]

One result is your primary battery is the source for ESS starts?
Which is more demand than original Jeep design.

In theory, the primary battery will wear out sooner?

that battery is always used for starts. The aux battery is for all the electronics that stay on while the jeep is off, taking the load off the main to preserve it for starting.

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[mbrose1994]

that battery is always used for starts. The aux battery is for all the electronics that stay on while the jeep is off, taking the load off the main to preserve it for starting.

Got it. Scenario is:

IF [ Disconnect the Auxiliary battery ]​

IF [ ESS button Active ]​

Primary battery must carry electronics load while engine OFF​

ELSE [ ESS button OFF ]​

Primary battery free from engine OFF electronics load​

To clarify:

Disconnecting the Auxiliary Battery NEG wire from the Primary Battery terminal is the only work required to eliminate the Auxiliary Battery operation.​

Pulling fuse 42 is just to stop a warning light on the dash.​

​

Seems only little benefit from physically removing the Auxiliary Battery.

 

[jav_eee]

Disconnecting the Auxiliary Battery NEG wire from the Primary Battery terminal is the only work required to eliminate the Auxiliary Battery operation.Pulling fuse 42 is just to stop a warning light on the dash.

that’s it. Upgrade your main battery to an H7 if you’re into that kinda stuff and you’re ready for anything.

 

[VKSheridan]

Like I said, I can’t explain why but it all works the way I want it to...no ESS, no aux battery, no need to push ESS button, no warning lights. Magic?

Not magic, design. Mine would have no ESS if I pushed the button to deactivate it and it would have ESS if the function was energized. I installed a Start/Stop Eliminator so it would remember to turn it off instead of me.

That said, I have heard of people who swear their ESS got disabled simply by pulling the auxiliary battery. I don’t believe in magic but I do believe in crappy design so maybe they have two of the right pins touching in a connector that other Jeep’s don’t. No clue

 

[AndySpill]

That said, I have heard of people who swear their ESS got disabled simply by pulling the auxiliary battery.

Those people Vince are speaking truth. Barring some of the early model year 2018's, which would fail to cold crank if adequate voltage was not found on the Aux battery (or that battery was disconnected), and who have not since had TSB 18-092-19 flashed at the dealer, later model 2018s and years thereafter are designed, if no or inadequate power is found on the Aux battery, to fail the crank, but in subsequent crank attempts seek to solely crank off the main battery, and if successful, turn on the ESS off light in the EVIC (dash), cranking on the first attempt thereafter.

That EVIC light remains on until, if at all, an Aux battery with voltage is retrofitted, or the factory wires leading to the Aux battery are modified to never be able to be isolated from the main battery, either by connecting them to the main, pulling fuse 42, or fused jumpering of N1 to N2 in the Power Distribution Center.

 

[mbrose1994]

Success, 90% level. Did the 2 most straight forward, least OEM modifying steps.

• Disconnected the AUX batt NEG cable end at the Primary batt.
• NOTE: On my JLU Sahara 2018, the AUX batt NEG cable end was attached to the extra post on the Primary batt NEG cable end. Beware, a YouTube video shows exactly opposite.
• Pulled F42 in fuse box.

The 10% NOT success is my center dash behind the steering wheel shows the ESS disable warning symbol. It is immediately above the top of the fuel level bar. The actual ESS button switch on the center console appears to work as normal. Start up is OFF, during run time pushing the button switch turns button indicator light ON. And second push turn button indicator light OFF.

The 90% SUCCESS is the ESS is disabled at start up and remains so. And the Dash Screen that shows the ESS system reports the ESS system is disabled or OFF.

So, not sure what pulling the F42 fuse actually does.
I could re-seat the F42 fuse and have the same result?

 

[AndySpill]

Success, 90% level. Did the 2 most straight forward, least OEM modifying steps.

• Disconnected the AUX batt NEG cable end at the Primary batt.
• NOTE: On my JLU Sahara 2018, the AUX batt NEG cable end was attached to the extra post on the Primary batt NEG cable end. Beware, a YouTube video shows exactly opposite.
• Pulled F42 in fuse box.

Hi Michael:

Did you electrically insulate the "Aux batt NEG cable end at the Primary batt," ideally with electric tape? If not, please do so.

As for where this cable connects to the main battery's negative post, member @Jebiruph has a post where he talks about how Stellantis changed, in different model years, where this cable connects. Perhaps the Youtube video you referenced features the newer connection point, given your 2018 model.

https://www.jlwranglerforums.com/forum/threads/ess-battery-cable-change.86624/

Before I continue, I want to handle your questions out of order and address what Fuse 42 does, because it's integral to your understanding here.

When Fuse 42 is in place the vehicle is capable of applying electrical current to the Power Control Relay (PCR). This is a device that when energized breaks the parallel connection between the two factory batteries: a parallel connection, at least from the factory that is always in place but for when the PCR is energized, which itself happens only for an instant at cold crank and during ESS events.

Yanking Fuse 42 silently, without diagnostic error on the part of the vehicle, prevents the PCR, which is a normally closed relay: meaning it establishing an electrical connection as long as no electrical power is applied to it, from ever being energized. Yank Fuse 42, and on your dual AGM battery JL all calls for electrical current to and from either battery now go to both batteries all the time (wait for it).... of which you only have the main battery connected now...so

...all calls for electrical current to and from either battery now go only to your main battery.

The 10% NOT success is my center dash behind the steering wheel shows the ESS disable warning symbol.

Your factory dual AGM battery JL, upon cold crank seeks to test the Aux battery alone, but can't because of the Fuse 42 pull. In instead, none the wiser, tests all available batteries, of which only your main remains and I strongly suspect finds your main battery (thinking it's the Aux battery) lacking in adequate voltage to allow ESS events, illuminating the ESS off light in the EVIC (dash).

It is immediately above the top of the fuel level bar. The actual ESS button switch on the center console appears to work as normal. Start up is OFF, during run time pushing the button switch turns button indicator light ON. And second push turn button indicator light OFF.

These two things you describe are to the vehicle separate functions. The ESS button allows you to prevent ESS events from happening should the vehicle otherwise detect ample battery power and not illuminate the ESS off light in the EVIC (dash.)

The 90% SUCCESS is the ESS is disabled at start up and remains so. And the Dash Screen that shows the ESS system reports the ESS system is disabled or OFF.

Yes, you've turned ESS off as a matter of speaking but the means by which this has happened concerns me. My best guess is that, given the cable and Fuse 42 pull, that it is a function of a main battery that may be lacking ample power and in need of replacement.

Lets suppose you had a brand new main battery. For argument sake you could simply yank the cable to the Aux battery and keep Fuse 42 in place. Your first attempt to crank would fail, as no ESS battery would be found when the PCR is energized (something that an happen because Fuse 42 is in place.) Provided you don't have an early 2018 (as this strands early 2018's without TSB 18-092-19) subsequent attempts to crank would happen off the main battery, and if successful, illuminate the ESS off light on the EVIC. Sounds great right. You've eliminated the Aux battery and turned ESS off without pressing buttons or buying tech.

I pondered the same thing. https://www.jlwranglerforums.com/forum/threads/this-confuses-me.123060/ @Jebiruph replied that he felt that pulling Fuse 42 to fool the vehicle into pre-crank testing the main battery, and keeping this ESS light in the dash from illuminated was a better play because the ESS light in the dash is a bit of a, to paraphrase, canary in the coal mine that when it illuminates can indicate trouble that can't be seen if the light is always on.

So, not sure what pulling the F42 fuse actually does.

We cover that above.

I could re-seat the F42 fuse and have the same result?

Yes, but if you got that same result it would mean different things depending upon whether you also reconnected the disconnected cable to the Aux battery.

If that cable were connected it would indicate that your Aux battery lacks ample power to effect ESS events.

If that cable were disconnected, the results are discussed above.

 

[mbrose1994]

[Reply to @AndySpill]
Thank you very much Andy for the in depth details. Yes, enables the understanding I need.
And, oh yes, did wrap the AUX batt NEG cable end very well. Gave it a little extra electrical tape. Then gave that tape a small bit of protective Duck tape.

To finish, as wisely advised in this thread, ZIP tied the wrapped, loose end, bent backwards along the Primary batt NEG cable. End result is cable secured and out of the way.

Superior long term looks like keeping F42 pulled. The ESS OFF indicator symbol is not a bother, is a valid dash alert to keep.

 

[zouch]

actually, the main battery was always the only source while cranking.
the Aux Batt does not get used for cranking; only for supplying power while ESS is engaged (engine stopped).

Pulling the aux battery changes the voltage sources while cranking from a pair of batteries to just a single source; The main battery.

 

[AndySpill]

actually, the main battery was always the only source while cranking.
the Aux Batt does not get used for cranking; only for supplying power while ESS is engaged (engine stopped).

Maybe Stellantis has changed the logic with vehicle flashes or new model years, but here's a video cranking solely with the Aux battery connected.....

 

[VKSheridan]

actually, the main battery was always the only source while cranking.
the Aux Batt does not get used for cranking; only for supplying power while ESS is engaged (engine stopped).

You are correct. Hence why I said you have two voltage sources during cranking, not two voltage sources for cranking.

 

[zouch]

actually, what you said was:
"cranking from a pair of batteries".

but glad we got that straightened out.

You are correct. Hence why I said you have two voltage sources during cranking, not two voltage sources for cranking.

 

[andy29847]

actually, what you said was:
"cranking from a pair of batteries".

but glad we got that straightened out.

Just to try and say this in a way that is clear.... the 2 Mopar batteries function as a single battery except for a start test (milliseconds) and an ESS event. An ESS event is when the batteries are separated, the aux battery supports cab functions, and the engine is off. The 2 batteries are reconnected and function as one to restart the vehicle after an ESS event.

Most of these threads about Jeep batteries start when one of the batteries fails the start test. The messages from this failure are varied for unknown (by me) reasons. It is difficult to identify which battery is weak, even with professional equipment and training. One of the points of discussion that stick in my mind is that the threshold for start test failure is ~12.4vdc. In my life, 12.4vdc indicates a good battery at 50-60% of its life. In other words, the batteries test good.

I've switched my JT to just one battery. Now the battery and charging system in my Jeep works much like all of the cars and trucks I have had for the last 50 years. The voltmeter in the dash actually is indicative of battery charge state. I have a premium H7 battery that has the same amount of cold cranking amps and the 2 Mopar batteries combined. My H7 battery also has a 4-year warranty. Peace of mind at last.

 

[zouch]

couldn't be much more complicated, could it? yes, it could,..

since the running lights also stay lit during an ESS event, *something* has to be powering them too; would that be the Main batt, or the Aux batt?

not that i really care; it's a stupid system that i'm happy to simplify by taking the Aux out of the equation.

Just to try and say this in a way that is clear.... the 2 Mopar batteries function as a single battery except for a start test (milliseconds) and an ESS event. An ESS event is when the batteries are separated, the aux battery supports cab functions, and the engine is off. The 2 batteries are reconnected and function as one to restart the vehicle after an ESS event.

Most of these threads about Jeep batteries start when one of the batteries fails the start test. The messages from this failure are varied for unknown (by me) reasons. It is difficult to identify which battery is weak, even with professional equipment and training. One of the points of discussion that stick in my mind is that the threshold for start test failure is ~12.4vdc. In my life, 12.4vdc indicates a good battery at 50-60% of its life. In other words, the batteries test good.

I've switched my JT to just one battery. Now the battery and charging system in my Jeep works much like all of the cars and trucks I have had for the last 50 years. The voltmeter in the dash actually is indicative of battery charge state. I have a premium H7 battery that has the same amount of cold cranking amps and the 2 Mopar batteries combined. My H7 battery also has a 4-year warranty. Peace of mind at last.

 

[andy29847]

couldn't be much more complicated, could it? yes, it could,..

since the running lights also stay lit during an ESS event, *something* has to be powering them too; would that be the Main batt, or the Aux batt?

not that i really care; it's a stupid system that i'm happy to simplify by taking the Aux out of the equation.

This is a wild ass guess, but since the running lights are controlled from the cab, I'd say they are running on the aux battery during a stop/start event.

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