Jumperless Aux Battery Bypass

[OldBob]

I made this mod and removed the aux batt completely. It has been a week and all seems fine except, and maybe unrelated, I walked by the Jeep last night and noticed the info section of the dash was illuminated with the put your foot on the brake to start message. I had to start and shut down the Jeep to go back to normal, all lights out.

Sponsored

 

[Yawnie'sPapa]

I made this mod and removed the aux batt completely. It has been a week and all seems fine except, and maybe unrelated, I walked by the Jeep last night and noticed the info section of the dash was illuminated with the put your foot on the brake to start message. I had to start and shut down the Jeep to go back to normal, all lights out.

Did you have the FOB on you?
Mine will do that if I have the FOB with me - it's like KITT, expecting me to jump in and go for a drive.

As long as all you do is remove the F42 fuse and take the aux battery out of service either by just pulling its ground cable or taking it clear out and leaving the other wiring in place, it's not going to hurt a thing.
*(didn't Jerry mention something like only 6 ESS stops per ignition cycle or something like that - ESS stops working after 6 times until you restart?)

The others have it right - the smaller of the two is the aux ground cable. It's the top of the two cables up through 2020, then in 2021 model year (either beginning or somewhere in between) they switched the two and the top cable became the main battery ground to the chassis and the bottom of the two - with the larger end and stud - is the aux battery ground.

 

[OldBob]

Yes, wife was standing by the Jeep and had FOB in her purse. I learn something here all the time, thanks.

I did remove the Aux Batt all together along with the fuse and disconnecting the ground cable. Also put a note in the Aux batt box and the fuse box so that when the next person comes along, they know that it is not as original.

 

[azwjowner]

Yes, wife was standing by the Jeep and had FOB in her purse. I learn something here all the time, thanks.

I did remove the Aux Batt all together along with the fuse and disconnecting the ground cable. Also put a note in the Aux batt box and the fuse box so that when the next person comes along, they know that it is not as original.

As someone who plans to totally remove the aux batt too one day, were there any difficulties? Does all the aux wiring cleanly separate from the rest? Did you jumper N1 to N3 or just leave the aux positive wiring in place and tape up the terminal holder?

 

[OldBob]

No jumper. Left wiring in place with the ends insulated (tape) just in case I or a future owner want to return to stock. Batt removed, no reason to carry the weight around.

 

[Fudster]

Did you have the FOB on you?
Mine will do that if I have the FOB with me - it's like KITT, expecting me to jump in and go for a drive.

As long as all you do is remove the F42 fuse and take the aux battery out of service either by just pulling its ground cable or taking it clear out and leaving the other wiring in place, it's not going to hurt a thing.
*(didn't Jerry mention something like only 6 ESS stops per ignition cycle or something like that - ESS stops working after 6 times until you restart?)

The others have it right - the smaller of the two is the aux ground cable. It's the top of the two cables up through 2020, then in 2021 model year (either beginning or somewhere in between) they switched the two and the top cable became the main battery ground to the chassis and the bottom of the two - with the larger end and stud - is the aux battery ground.

Pulling Fuse 42 prevents the dual battery JL from isolating the batteries as wired from the factory: which happens in two situations under factory wiring, ESS events and an instant at cold crank.

Were you to not turn off ESS while running with one battery that ESS event will run off the main battery and its voltage (the dual battery JL thinking it's tapped the ESS battery when it''s tapped the main battery) will compare its voltage to.....

the main battery.

Which will of course have the same voltage.

When this happens 6 times in one cold crank the dual battery JL assumes there is a short and disables ESS until the next cold crank.

This factoid is, I hope in large part academic, as not engaging ESS with one battery on dual battery JLs is probably a good practice, as you are robbing your cranking battery of power during the ESS events.

If you forget to turn ESS off and you run with one battery--it's not "crossing the beams in the movie Ghost Busters." But the perfect storm of a main battery on its way out, a cold night, and lots of appliances running *might* find the vehicle early terminating the ESS event due to a voltage drop in the battery--energizing appliances in the ESS event without the alternator running--at just the point where inadequate voltage exists to crank the engine.

I haven't heard of anyone reporting this, but it's IMHO not worth the $0.02 in gasoline savings to got stranded, particularly at a traffic light in the middle of a busy road.

 

[Yawnie'sPapa]

My wife and I have both noticed the fuel savings of ESS for our driving - we leave it enabled. In fact, when her 2018 batteries were on their way out she asked "why isn't it stopping any more".
I did some checking and determined the main battery wasn't taking and holding a charge for very long at all. Dealer replaced them both under warranty.

I've dealt with batteries and such for a long time (it's been part of my career) so I'm not real worried about anything. I read the signs, I do occasional checks on systems, preventative maintenance and so on. I resolved the issues with my 2020 by charging both batteries independently with a proper charger and resetting the IBS and putting it all back together. It worked fine after that until I traded it.
(I note that the charging voltages on the 2022 are higher than they were on my 2020 - did Jeep make a change?)
I've noticed that even if the timeout isn't reached for ESS to restart things, that if the batteries get low enough it will restart the thing sooner than usual. Doubtful it's going to leave you stranded.
I've also noticed something interesting - I ran leads into my JT's cab - one from the main battery positive and one from the N1 terminal and took volt meters in the cab and watched voltages during ESS stops. The main battery voltage drops at a similar rate to the aux battery dropping. It's often about a tenth to half a volt behind. I suspect it's because the fans, EHPS and some other items are pulling directly from the main battery at all times via the high current fuse array.

As long as your battery is healthy still has capacity (as opposed to CCA or just plain "voltage", it's likely to start at the end of an ESS stop event due to the fact that the PCM has things lined up for a fast start, and the starter doesn't draw hardly anything on those starts. You could start that thing on a lawn tractor battery.

The more these batteries sit - not being driven daily, and the more they are used for short drives of 30 minutes or less, the faster they will lose capacity. They are being cycled and never fully charged up again. That's where there will be trouble after a couple years or so.
If they are kept charged, and not allowed to sit for days with parasitic draw of the Jeep's systems, and are taken for long drives at higher RPM and road speeds, instead of being used for short daily commutes or grocery-getting, they'll live longer and hold capacity longer.
When people drive them to work 10 miles, then home again and park them........ or if they drive them maybe a couple of times a week - that's when things get iffy.

 

[Fudster]

...I've noticed that even if the timeout isn't reached for ESS to restart things, that if the batteries get low enough it will restart the thing sooner than usual. Doubtful it's going to leave you stranded.

I both hope so and agree Bill. But you are describing a situation I presume, with both batteries connected as per factory, where the main battery is (in large part, so below) sparred during the ESS event, precisely so its power is available to effect the [bulk of the] crank (in actuality both batteries are brought back into parallel an instant before the post ESS crank.)

..and I think you'd 99 times out of 100 be safe running ESS with one battery. I advise against it though on a rewards/cost basis, where, as said, saving $0.02 in gasoline is not IMHO worth the risks/dangers of an post ESS event inability to crank, say at a traffic light in a major intersection, where the "perfect storm" of factors is at play: old battery, lots of appliances on, cold night, etc.

The issue is whether the engineers at Stellantis set a higher enough voltage threshold for ESS to end prematurely even if running one battery. I simply haven't compared such voltages thresholds to those in one battery ESS vehicles, and think such comparisons would only be fair if the vehicles being compared to are running no less aftermarket energy hungry appliances, as a JL/JT owner is more likely to be.

I've also noticed something interesting - I ran leads into my JT's cab - one from the main battery positive and one from the N1 terminal and took volt meters in the cab and watched voltages during ESS stops. The main battery voltage drops at a similar rate to the aux battery dropping.

While that's a somewhat surprising and interesting finding, perhaps such voltages differences might be more pronounced in JLs/JTs equipped with more (and energized) aftermarket appliances that you have installed. I of course can't speak to your setup.

And, as a battery knowledgeable person, you must realize that voltage is but one snapshot in time metric, the real gold standard being the ability for a battery to deliver and accept a load (i.e. load testing.)

As you comment below, I'm to understanding that some vehicle appliances do continue to tap the main battery during ESS events. I think I read that Jerry @Jebiruph once concluded that, for example, power steering always draws from the main battery, even in ESS events, and perhaps, because of this fact, when the steering wheel is turned too far in either direction before an ESS event, ESS won't engage.

The more these batteries sit - not being driven daily,

Agreed. And I'm one of those souls. The exception being though those of us, like me, that keep our JLs/JLts on a trickle charger when parked: the electrical expense of doing so counterbalancing the savings in gasoline during ESS evens duly noted.

 

[Yawnie'sPapa]

While that's a somewhat surprising and interesting finding, perhaps such voltages differences might be more pronounced in JLs/JTs equipped with more (and energized) aftermarket appliances that you have installed. I of course can't speak to your setup.

In my case, nothing running that the factory didn't include. Winch is always disconnected except when in use, no after-market lights other than Oracle backup lights - off when sitting. No added loads.
When mine was stopped for ESS stop events, it was basically a factory setup, wheels straight ahead.

When the batteries are both up, fully charged, and the running voltage of the truck has dropped indicating they are likely charged (and I measured the battery voltage to be 12.6 or higher with them connected) the voltage dropped much more slowly when stopped for ESS than when the voltages were just high enough to allow an ESS stop. Cold weather also mattered of course.
Makes sense.

We know that EHPS always draws from the main battery - just by looking at the high current fuse array. EHPS is powered off that array. And that array bus is connected directly to the main battery and to the alternator (via fuse)
Cooling fan is also powered directly from the main battery via the high current fuse array (through its fuse in that array)
One needs no discovery, looking at the fuse array or the chart on the inside of the PCD cover shows that.

Most accessories, other than communications equipment (CB, etc.) or coolers, fridge, etc.) are likely to be turned off when in town. The running after-market accessory isn't likely to play into things so much when on city streets.

I'm unlikely to do any type of battery bypass anyway. It's just not going to be a problem for us.
But if I did for some reason, I watch gauges. I've always run full gauges in my cars - voltage, oil pressure, etc. I even put the rally gauges in my 73 (that thing is a pain in the butt because it's so modified. I need transmission temp gauge in that thing, too.)




CCA = sprint capacity - can it muster a lot of amps quickly for a short time, crank over in cold weather and not drop voltage below xx volts. Important for Canadians LOL Can it crank the engine for 30 seconds at 0 degrees and not drop voltage. Not important for a tiny Toyota engine, very important for a diesel of large V8.

Capacity =marathon use - how long can it handle xx amps and not drop below yy volts.
Capacity is going to be important for vehicle that sit with these parasitic draws for long periods.

 

[jhrodd]

No auto maker does everything right but Ford did give me a credit to remove ESS from the build sheet.

 

[KOKOKO]

Anyone bypass the AUX on a newer JLU? Neg terminal from AUX does not wire directly to MAIN battery. 2021 JLU w/tow and aux switches. Main battery showing signs of failure (aux switches disabled for low battery at startup). ESS disabled via tazer.

 

[Fudster]

Anyone bypass the AUX on a newer JLU? Neg terminal from AUX does not wire directly to MAIN battery. 2021 JLU w/tow and aux switches. Main battery showing signs of failure (aux switches disabled for low battery at startup). ESS disabled via tazer.

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

 

[KOKOKO]

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

Not questioning which cable is which. I only have one cable attached to the main neg terminal. I assume the aux is bonded at the chassis or frame. Asking if anyone can confirm where?

Resolved with a little help. No aux battery to complain about.

 

[Rhinebeck01]

Not questioning which cable is which. I only have one cable attached to the main neg terminal. I assume the aux is bonded at the chassis or frame. Asking if anyone can confirm where?

It seems, you do not have have a dual battery system, JL. One cable on the Main's negative in regard to a stock JL tells me that.

 

[KOKOKO]

It seems, you do not have have a dual battery system. One cable on the Main's negative in regard to a stock JL tells me that.

ESS with main only from the factory?

Sponsored