Question about fuse 42 removal

[MrMischief]

The main battery in my 2019 3.6L finally died. While replacing it I figured I would do the by pass of the smaller battery at the same time. I don’t really have a problem with ESS but mine hasn’t worked for years now, my voltage meter on the dash always showed around 14.4 volts and the ESS screen always said something about battery charging. So I removed fuse 42 and disconnected the negative lead to it from the main battery. Jeep started just fine, while driving the voltage meter showed 14.1 volts, and when I stopped at my destination the Jeep shut off, to my surprise. When I let off the brake it restarted. I wasn’t expecting that behavior but in reading some other posts I guess I should just leave the ESS Off function enabled (button lit). So I do my thing and drive home. What stood out to me is that now while driving home the voltage showed about 12.8 volts unless coasting it would hop up to around 14.1 volts. I suspect this is the correct behavior as the smart alternator does its thing, but can someone confirm this please. Tomorrow I’m driving several states to prepare for my father’s funeral and really don’t want to be stranded over another dead battery because I screwed something up.

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[Dgr401]

Sorry for your loss. I have not disconnected the negative or pulled fuse 42 yet but I have seen my voltage do the same - 12/13V driving and jumps up to 14+ while idling. From what I understand pulling the fuse and disconnecting the negative shifts the ESS function to the main battery, if you don’t want the ESS function you still have to push the button.

 

[Mx5red]

ESS still happens, you just took the aux battery out of the equation so it won't parasitically draw off your main battery since they're different capacities. I'd still keep pushing the button and bypassing ESS (or buy an electronic bypass).

 

[Gregj]

Sorry for your loss.

Your charging system is functioning as designed and your main battery is charged and in good health.
Gregj

 

[Beachcomber72]

Sorry to hear of your loss sir,

Are we sure that you have a 3.6 with aux battery or is your engine the 3.6 w/etorque?

 

[rohdawg]

while driving home the voltage showed about 12.8 volts unless coasting it would hop up to around 14.1 volts. I suspect this is the correct behavior as the smart alternator does its thing, but can someone confirm this please.

That’s the correct behavior. It’s doing what it’s supposed to be doing.

 

[MrMischief]

Sorry to hear of your loss sir,

Are we sure that you have a 3.6 with aux battery or is your engine the 3.6 w/etorque?

Definitely the aux. I had the little battery die on me in ~April 2020 and I replaced it myself rather than mess with the dealer. While replacing this big one I got to thinking I didn’t also want to do the small one because I found it to be a bit of a pain, so I pulled the fuse instead.

Thank you everyone for the confirmation, seems things are working as they should. I have a tazer mini which should help with the annoyance of pushing the ESS button each startup.

 

[Rhinebeck01]

Since the word "etorque" was mentioned in a post in this thread, that is talking fuse F42 removal.....

Just to clarify ---> etorque JL's, do not have a fuse in the F42 slot of the PDC (power distribution center)... again, no F42 fuse /just a vacant F42 slot.

 

[MrMischief]

ESS still happens, you just took the aux battery out of the equation so it won't parasitically draw off your main battery since they're different capacities.

So I'm driving down the interstate, bored out my mind and I look at the ESS screen on my dash. Of course it says "ESS Off" because I have the button pushed. I hit the button and it says "ESS Ready". I hadn't seen that message in years. I pull off for gas and yep sure enough ESS works. And it seems like everything else is still powered. Sssoooo..... what is the point of the little battery again? As I understand it the reason to remove the little battery is that so when it dies it does not also kill the big battery. But why does it even exist? Debating hooking the little one back up for my 500 mile drive home to see what happens. On the way out here there's a timeline to keep. On the way back the worst thing that happens is I have a bit of an adventure.

 

[AndySpill]

So I'm driving down the interstate, bored out my mind and I look at the ESS screen on my dash. Of course it says "ESS Off" because I have the button pushed. I hit the button and it says "ESS Ready". I hadn't seen that message in years. I pull off for gas and yep sure enough ESS works. And it seems like everything else is still powered. Sssoooo..... what is the point of the little battery again? As I understand it the reason to remove the little battery is that so when it dies it does not also kill the big battery. But why does it even exist? Debating hooking the little one back up for my 500 mile drive home to see what happens. On the way out here there's a timeline to keep. On the way back the worst thing that happens is I have a bit of an adventure.

The "little" battery is there to power most of your appliances during an ESS event, sparing the main battery, which bears the bulk of the load in re-cranking your vehicle after the ESS event is done on dual AGM battery JLs.***

At ESS event conclusion, but prior to re-crank both batteries are brought back into parallel with each other on dual AGM battery JLs to provide current to the engine starter.

Stellantis feared, I reason, designing ESS on a JL, with the potential for considerable aftermarket current drawing appliances, with one battery, like most other auto makers, fearing such appliances could drain down the one battery enough, before the vehicle ends the ESS event early due to low voltage, to be unable to restart the engine.

*** I think member Jebiruph found some things in the dual AGM battery JL that run off the main battery in ESS events like power steering..which interestingly enough--may very well be why when the steering wheel is turned too much, it is one of the conditions (of many) in which ESS won't engage.

 

[THAW]

I don’t really have a problem with ESS but mine hasn’t worked for years now, my voltage meter on the dash always showed around 14.4 volts

What stood out to me is that now while driving home the voltage showed about 12.8 volts unless coasting it would hop up to around 14.1 volts.

I hit the button and it says "ESS Ready". I hadn't seen that message in years. I pull off for gas and yep sure enough ESS works. And it seems like everything else is still powered. Sssoooo..... what is the point of the little battery again?

Your ESS likely didn't work previously because your ESS battery didn't pass the voltage test.

You were likely seeing 14.4 volts because your dead ESS battery pulled down the voltage of your combined batteries such that the smart alternator system didn't read a sufficiently charged state to reduce voltage.

When you bypassed the dead ESS battery and pulled fuse 42, your main battery took and passed the ESS battery voltage test, re-enabling ESS functionality. Your smart alternator read a reasonable SOC and reduced voltage.

The point of the separate ESS battery is at least in part to ensure the main battery isn't discharged by system electronics during ESS events to the point it can't start the vehicle.

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