Push to start not working first try. Second try works fine.

[Nevaehd]

The dual AGM batttery JL will normally attempt to isolate the Aux battery for an instant when the operator attempts to cold crank the vehicle, so that this battery alone can be tested for voltage to see if it has adequate power to run ESS events.

The status of the ESS button in the dash does not change this startup procedure.

If the Aux battery has inadequate power the crank will fail, but subsequent attempts to crank will--provided you don't have an early 2018 that lacks TSB 18-092-19--be effected solely against the main battery, and if successful, turn the ESS off light (the "A" with a near circle surrounding it, and a slash through it) on in the dash.

Is this what is happening to your dash?

All subsequent cold cranks will still test the Aux battery but if it fails, repeat this procedure automatically trying the crank against the main battery, and if successful at getting just the main battery to crank the engine, keep this ESS off light illuminated in the dash.

When this light is on ESS events can't occur: this light having no connection to the ESS off button.

Not until the next cold crank in which an energized Aux battery is detected, if any, or the JL is tricked as per the below procedure, will this light in the dash shut off.

I would replace both batteries, or just the main battery and disconnect and bypass the Aux battery provided you are willing to not run ESS events.

Disconnecting and bypassing the Aux battery involves at minimum pulling Fuse 42 in the Power Distribution Center and removing the factory cable on the main battery's negative post that does NOT have as its other end the body ground on the passenger's front quarter panel. The end of that disconnected cable should be insulated. This disconnected cable at its distal end connects to the negative post of the Aux battery which pulling this cable off the main battery's negative post removes the Aux battery from the electrical schematic of the vehicle, no longer delivering or receiving charge.

Pulling Fuse 42 prevents the Aux battery from ever being isolated such that calls for it to exclusively provide power, either in ESS events, or the pre-crank test, now go to all available batteries, of which the aforementioned cable pull leaves you with just the one main battery.

It is recommended that you turn ESS off if you take this fuse and cable pull route. Expect the light in the dash to turn off with just a new main battery and the Fuse and cable pull as the pre crank test succeeds against solely the main battery, the vehicle none the wiser that it mistakenly tested the main battery given the fuse pull, unable to energize the normally clsoed relay that when energized (which requires at intact Fuse 42) separates the batteries

Turning ESS off is recommended when eliminated the Aux battery so as to not run ESS events against the main battery, it normally being spared during ESS events under the factory configuration, to bear the bulk of the cranking effort when ESS events terminate.

thank you so much for your response. Will do. This morning my service engine light came on. Would you suspect this is a result ?

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[Nevaehd]

it’s a 2018 JLU with 80,000 miles. I’ve been more aware of pushing the break harder but it seems to still keep doing it every morning

I hear two lights came on today

 

[Nevaehd]

thank you so much for your response. Will do. This morning my service engine light came on. Would you suspect this is a result ?

 

[Nevaehd]

The dual AGM batttery JL will normally attempt to isolate the Aux battery for an instant when the operator attempts to cold crank the vehicle, so that this battery alone can be tested for voltage to see if it has adequate power to run ESS events.

The status of the ESS button in the dash does not change this startup procedure.

If the Aux battery has inadequate power the crank will fail, but subsequent attempts to crank will--provided you don't have an early 2018 that lacks TSB 18-092-19--be effected solely against the main battery, and if successful, turn the ESS off light (the "A" with a near circle surrounding it, and a slash through it) on in the dash.

Is this what is happening to your dash?

All subsequent cold cranks will still test the Aux battery but if it fails, repeat this procedure automatically trying the crank against the main battery, and if successful at getting just the main battery to crank the engine, keep this ESS off light illuminated in the dash.

When this light is on ESS events can't occur: this light having no connection to the ESS off button.

Not until the next cold crank in which an energized Aux battery is detected, if any, or the JL is tricked as per the below procedure, will this light in the dash shut off.

I would replace both batteries, or just the main battery and disconnect and bypass the Aux battery provided you are willing to not run ESS events.

Disconnecting and bypassing the Aux battery involves at minimum pulling Fuse 42 in the Power Distribution Center and removing the factory cable on the main battery's negative post that does NOT have as its other end the body ground on the passenger's front quarter panel. The end of that disconnected cable should be insulated. This disconnected cable at its distal end connects to the negative post of the Aux battery which pulling this cable off the main battery's negative post removes the Aux battery from the electrical schematic of the vehicle, no longer delivering or receiving charge.

Pulling Fuse 42 prevents the Aux battery from ever being isolated such that calls for it to exclusively provide power, either in ESS events, or the pre-crank test, now go to all available batteries, of which the aforementioned cable pull leaves you with just the one main battery.

It is recommended that you turn ESS off if you take this fuse and cable pull route. Expect the light in the dash to turn off with just a new main battery and the Fuse and cable pull as the pre crank test succeeds against solely the main battery, the vehicle none the wiser that it mistakenly tested the main battery given the fuse pull, unable to energize the normally clsoed relay that when energized (which requires at intact Fuse 42) separates the batteries

Turning ESS off is recommended when eliminated the Aux battery so as to not run ESS events against the main battery, it normally being spared during ESS events under the factory configuration, to bear the bulk of the cranking effort when ESS events terminate.

Thank you for the detailed response!!! Would a service engine light be related? This just popped up this morning.

 

[AndySpill]

Thank you for the detailed response!!! Would a service engine light be related? This just popped up this morning.

A service engine light could conceivably--in fact pretty much any diagnostic error the vehicle is capable of producing--be the result of the vehicle, metaphorically "losing its mind" as a result of running a battery or batteries in need of replacement.

If I were in your shoes I would have the main battery replaced if original equipment, or at the very least load tested, and if said tests show it "shot," then replaced and the Aux battery bypassed and ESS turned off by you. Alternatively, if either battery is shot, replace both and keep the batteries wired as per factory spec, running or not running ESS events as you see fit.

Many a diagnostic error will clear itself when ample battery power is available. If not, you likely needed the new battery/ies anyway, and knowing that you are running with new batteries and still getting such service engine light will add legitimacy to that diagnostic being accurately reflective of a true problem in need of dealer service.

Good luck.

 

[azjl#3]

Depending on the age of the vehicle and/or the batteries, the wonky Start button functioning may indeed be linked to one or both batteries approaching the end of their practical service life.

That said, once in a blue moon I'll catch myself pressing the brake pedal too lightly, just enough to disallow an engine start, but the dash lights and self-diagnostics (evident via the needle sweeps) will illuminate and cycle as usual.

this^^ I unfortunately note my brake pedal is dead, after sitting over night. Unlike the 50 years of brakes I have owned which can at least hold a vacuum over night.

 

[AndySpill]

I'm sorry, I mildly misspoke. The ESS off light in the dash appears as the letter "A" with a near circle around it followed by an exclamation point as shown in your picture OP, not this letter and circle with a slash through it as I originally reported.

 

[zouch]

actually, the Aux Batt is not for starting; it's only to keep everything else lit while the engine is stopped for an ESS event.

<snip>
Wouldn't the main battery be used for cold starts? The ESS battery is exactly that: intended for warm restarts when the driver lifts his foot off the brake pedal.

 

[zouch]

sorry if i missed it, but are you on the original batteries?
are you the original owner?

i think it amazing you could have gotten this far on the original batteries.

sounds like your Aux Batt is dead causing the system to fail its start-up check, necessitating a restart where it bypasses the Aux Batt check, but i believe this behavior varies with the software on the vehicle.

i'd be replacing both batts with a couple of decent AGMs post haste.

it’s a 2018 JLU with 80,000 miles. I’ve been more aware of pushing the break harder but it seems to still keep doing it every morning

 

[AndySpill]

actually, the Aux Batt is not for starting; it's only to keep everything else lit while the engine is stopped for an ESS event.

The above needs clarification.

The Aux battery, as per the factory spec participates in providing power in engine cranks along with the main battery: cold and post ESS event alike--the main battery bearing most of the responsibility for turning over the engine.

If your Aux battery has ample power it can crank your vehicle even without the main battery (connected.)

That said, saying that the Aux battery isn't (designed) for starting is a true statement. The vehicle is designed for the power needed to effect the crank to come mostly from the main battery.

 

[Heimkehr]

 

[THAW]

The Aux battery, as per the factory spec participates in providing power in engine cranks along with the main battery: cold and post ESS event alike--the main battery bearing most of the responsibility for turning over the engine.

Genuine question: is there documentation the PCR closes prior to ESS starts?

 

[AndySpill]

Genuine question: is there documentation the PCR closes prior to ESS starts?

I remember reading about this; I will try to find the source.

That said, with the PCR relay energized and open I don't mean to imply that the main battery can't, say during ESS event be tapped. In fact when Jerry @Jebiruph did the initial testing on this I think he found some things on the dual AGM battery JL that tap the main battery, like power steering, even during ESS events.

Thoughts Jerry?

https://www.jlwranglerforums.com/forum/threads/drained-battery-any-jumpstart-tips.12316/post-981215

 

[THAW]

In fact when Jerry @Jebiruph did the initial testing on this I think he found some things on the dual AGM battery JL that tap the main battery, like power steering, even during ESS events.

The EHPS (power steering) and radiator fan are connected to the main/crank battery through the Z Case Fuse Array so are physically unaffected by PCR state.

 

[Kyanche]

sorry if i missed it, but are you on the original batteries?
are you the original owner?

i think it amazing you could have gotten this far on the original batteries.

sounds like your Aux Batt is dead causing the system to fail its start-up check, necessitating a restart where it bypasses the Aux Batt check, but i believe this behavior varies with the software on the vehicle.

i'd be replacing both batts with a couple of decent AGMs post haste.

SOME OF US! My 2020 (just a couple weeks past 5 years old and 10,600 miles) just did exactly what's being posted in here today lol.

Time for new batteries. Yep yep. I was planning to proactively swap them, but got curious how long the originals would go since they seemed to crap out on everyone at the 3 year mark.

For further humor, the battery in my JK only lasted about 4 years lol.

Mine took 2 tries to start and gave me a check engine light but seemed to be running fine otherwise. I was really busy today so I was planning to put a code scanner on it in the morning and probably go battery shopping. Glad to see it's probably just batteries. Woo.

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