Jumperless Aux Battery Bypass

[Rhinebeck01]

Replacing my main battery today. Bypassing aux.

I have a 2020 JLUR 2.0

I was jumping it off every crank but now it won’t even do that. Went and pulled the f42 fuse and removed the cable I thought was the aux battery cable. The one with the smaller terminal connector. Things went nutty. Assuming maybe the main just has such a low charge that it is causing the glitches? My wipers started going, emergencies flashing, fuse box sounding like a typewriter clicking lol.

Read somewhere and can’t find now that they changed the cable ends at some point? That the larger terminal end is the end of the aux negative cable.

?

thanks!

@Memcdowe

You misunderstood what you read apparently.

It is not the connector / "terminal" size that clues you in to which cable is the Aux negative cable.. It is the diameter of the cable itself. The slightly smaller diameter cable is always the Aux negative cable.

I strongly encourage you to read at the link I am posting below BEFORE you fool with/ go to change out the Main battery. Knowledge found there will keep you from doing costly damage.... will also point you to best Main to buy, etc.
https://www.jlwranglerforums.com/forum/threads/??-main-battery-replacement-talk-jl-jt.100534/

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[Memcdowe]

@Memcdowe

You misunderstood what you read apparently.

It is not the connector / "terminal" size that clues you in to which cable is the Aux negative cable.. It is the diameter of the cable itself. The slightly smaller diameter cable is always the Aux negative cable.

I strongly encourage you to read at the link I am posting below BEFORE you fool with/ go to change out the Main battery. Knowledge found there will keep you from doing costly damage.... will also point you to best Main to buy, etc.
https://www.jlwranglerforums.com/forum/threads/??-main-battery-replacement-talk-jl-jt.100534/

No, I understood. Slightly smaller is what I went with. Going to check with meter when I get home and replace main.

No need for condescension. Let’s not let this forum turn into what the other place ran by gut that got banned is like.
It’s just to easy not to drop little snarky comments in your responses.

 

[Rhinebeck01]

No, I understood. Slightly smaller is what I went with. Going to check with meter when I get home and replace main.

No need for condescension. Let’s not let this forum turn into what the other place ran by gut that got banned is like.
It’s just to easy not to drop little snarky comments in your responses.

How the frig was that reply condescending or snarky..

To say I think you misunderstood is not condescending or snarky.

I'll refrain from any comments to you in the future.

 

[Jammer]

Last year I could not get my motor to cut off I disconnected the big battery cable and it kept running they told me the auxiliary battery had gone bad luckily it finally shut off I don't know what I would have done someone said you can pull a fuse but I can't remember which one it is

 

[Memcdowe]

Replaced main. Removed f42 fuse. Removed and taped up negative cable going to aux.

Two days of showing homes and starting stopping at a lot of places. No issue. ?

 

[stingGreyNJ]

Replaced main. Removed f42 fuse. Removed and taped up negative cable going to aux.

Two days of showing homes and starting stopping at a lot of places. No issue. ?

This is the way. I've been weeks with a new Main, no f42, and negative pulled from Aux. Recommend this change to all.

 

[namodei]

While working on another project, I was looking at the fuse descriptions on the underside of the PDC cover and saw this - F42 PCR CTRL FEED (ESS)*. Could it really be this easy? Yes it is. I pulled the fuse, disconnected the aux negative cable from the main battery negative post and it started right up without any errors.

Unplugging the PCR has always been an alternative to using an N1 N2 fused jumper, both methods defeat the aux battery pass/fail test that occurs prior to a cold start. Unlike using a jumper, unplugging the PCR doesn't require any additional parts, it's just not easy to get to the PCR plug. Removing the F42 fuse accomplishes the same thing as unplugging the PCR and the fuse is easy to get to.

Other than a couple starts, I haven't had the chance for real world testing, but I did look at the schematic and verified that pulling the fuse accomplishes the same thing as unplugging the PCR, both prevent the relay from activating.

Here's the underside of the PDC cover showing the description and location of the fuse.

Here's the fuse location with the fuse removed.

Here's the schematic showing the fuse in the circuit.

Does TSB 18-092-19 need to be performed in order for this aux battery bypass to work? I have a 2018 with a January 2018 build date, that I know does not have this TSB performed.

 

[Rhinebeck01]

.

Does TSB 18-092-19 need to be performed in order for this aux battery bypass to work? I have a 2018 with a January 2018 build date, that I know does not have this TSB performed.

@namodei

No.

 

[namodei]

.


@namodei

No.

Hello, just replaced the main battery with brand new battery, and did the bypass per the instructions. Im now getting stop start not ready battery protection mode. Any ideas??

 

[namodei]

Hello, just replaced the main battery with brand new battery, and did the bypass per the instructions. Im now getting stop start not ready battery protection mode. Any ideas??

Got it! Reset the IBS and all works great!

 

[Rhinebeck01]

Got it! Reset the IBS and all works great!

Just saw your post or I would have replied sooner.... Glad you got it worked out.

I have been pretty busy.

In the last 3 days, I have changed out 3 Aux batteries and 3 Main batteries on other peoples JL's. I did manage to get one other guy to just have me do the jumper-less bypass on his JL.

Anyway, I'm sure you will soon be saying to yourself.... Why did I not do an Aux battery bypass sooner..

 

[Fudster]

Does TSB 18-092-19 need to be performed in order for this aux battery bypass to work? I have a 2018 with a January 2018 build date, that I know does not have this TSB performed.

Nick:

You correctly got your "no" but there's more to it than that, that you should know. The short version is turn ESS off. The explanation as to why follows:

TSB 18-092-19 affects some changes to the JL inside and outside the realm of the batteries and their logic, but discussion of other than batteries and logic is off topic.

The functionality of TSB 18-092-19, whose logic you seem to appreciate is built into most but the earliest JLs, changes what happens during the vehicle's pre-crank instantaneous isolation and testing of the Aux battery (the same battery you've bypassed,) if said testing shows the battery as dead.

Assuming factory wiring, which you've changed and I'll cover, prior to TSB 18-092-19, you were stranded if your Aux battery was dead. Subsequent to the TSB, while your attempt to crank will still fail if that Aux battery is dead, future attempts to crank after than will be tried by the vehicle solely off of the main battery. If successful, the vehicle will turn ESS off, letting you know as such in the dash. All future engine cranks will happen on the first try, and that ESS off light will not go away until the next crank, if any, where an energized ESS battery (again, based on stock wiring--which you now don't have) is detected.

Your jumper tricks your JL such that calls it thinks it makes (only to) the ESS battery are actually now rerouted to the main battery.

In a stock dual AGM battery JL like yours, the batteries are always connected in parallel but an instant during this pre-crank test, and during ESS events. Jumper the batteries like you did, but don't disconnect the ESS battery (which you DID do) and the two batteries are always in parallel.

Jumper the batteries and disconnect the ESS battery (your direction) and all calls for battery power by the vehicle to any and all batteries always are energized now from solely the main battery.

That said, let's talk about how the installation of your jumper affects things. With its placement and your bypassing of the Aux battery, as stated, all calls to what the vehicle thinks is the Aux battery get channeled to the main battery. That pre-crank test goes against the main battery now. Had you not disconnected the ESS battery with that jumper, nothing the JL could do would isolate that ESS battery, even though it would still be tapped for power. Attempts by the vehicle to solely tap that ESS battery it would get routed to both batteries, meaning ESS events would run on both batteries.

But given your disconnect of the ESS battery in addition to the jumper, ESS events will now only tap your main batteries to run appliances with the engine shut down at a stop lights.

This fact is why it's recommended that you don't run ESS under your new jumpered setup, even if you still had the ESS battery connected.

The whole idea of separating the dual stock batteries in an ESS event was to preserve the main battery for engine cranking. Specifically, once the vehicle terminates the ESS event, either because you've taken your foot off the brake, or the ESS battery voltage has run low, or you've done something that is inconsistent with being in ESS (e.g. put an automatic in a manual gear) both batteries on a stock JL are brought back into parallel to both energize the crank of the engine, the main battery bearing, not taxed in the ESS event, most of the brunt of that work. In your case only the main battery runs an ESS event and then, partially drained from the ESS event, attempts to crank the engine.

In either case, ESS battery connected or not, ESS events with your jumper in place rob the main battery of cranking power: more so in your case given there's only one battery. The vehicle's monitoring of that ESS battery's voltage during ESS events , or so it thinks, to early terminate the ESS event if the ESS battery's voltate runs too low, is really now, because of your wiring change and ESS battery disconnect, just an assessment of the voltage of your main batttery.

(Had you not disconnected the ESS battery the voltage assessment of what the vehicle thinks is the ESS battery in ESS events would have been a composite voltage of both batteries.)

In theory your ESS event could last longer than it should were it only running off the ESS battery (because the main battery has more capacity.) Additionally you could risk not having enough power in the main battery to effect an engine crank once the light turns green because that main battery was drained in the ESS event. So turn ESS off when using a jumper, especially if you are bypassing the ESS battery. How you turn off ESS, buying tech or pushing the ESS off button at crank is all fine by me.

Your jumper and disconnection of the ESS battery does permanently and exactly what TSB 18-092-19 does in factory wiring if after a crank attempt, the Aux battery is dead, but the main battery has enough power to crank on the second and all subsequent cranks.

The difference between the two is that your jumper doesn't automatically turn ESS off while the TSB does if what it "thinks" is the Aux battery (i.e. if you don't change factory wiring) is dead.

So turn ESS off yourself.

(Yes, some vehicles are designed to run ESS with one battery. The JL isn't.)

 

[namodei]

Nick:

You correctly got your "no" but there's more to it than that, that you should know. The short version is turn ESS off. The explanation as to why follows:

TSB 18-092-19 affects some changes to the JL inside and outside the realm of the batteries and their logic, but discussion of other than batteries and logic is off topic.

The functionality of TSB 18-092-19, whose logic you seem to appreciate is built into most but the earliest JLs, changes what happens during the vehicle's pre-crank instantaneous isolation and testing of the Aux battery (the same battery you've bypassed,) if said testing shows the battery as dead.

Assuming factory wiring, which you've changed and I'll cover, prior to TSB 18-092-19, you were stranded if your Aux battery was dead. Subsequent to the TSB, while your attempt to crank will still fail if that Aux battery is dead, future attempts to crank after than will be tried by the vehicle solely off of the main battery. If successful, the vehicle will turn ESS off, letting you know as such in the dash. All future engine cranks will happen on the first try, and that ESS off light will not go away until the next crank, if any, where an energized ESS battery (again, based on stock wiring--which you now don't have) is detected.

Your jumper tricks your JL such that calls it thinks it makes (only to) the ESS battery are actually now rerouted to the main battery.

In a stock dual AGM battery JL like yours, the batteries are always connected in parallel but an instant during this pre-crank test, and during ESS events. Jumper the batteries like you did, but don't disconnect the ESS battery (which you DID do) and the two batteries are always in parallel.

Jumper the batteries and disconnect the ESS battery (your direction) and all calls for battery power by the vehicle to any and all batteries always are energized now from solely the main battery.

That said, let's talk about how the installation of your jumper affects things. With its placement and your bypassing of the Aux battery, as stated, all calls to what the vehicle thinks is the Aux battery get channeled to the main battery. That pre-crank test goes against the main battery now. Had you not disconnected the ESS battery with that jumper, nothing the JL could do would isolate that ESS battery, even though it would still be tapped for power. Attempts by the vehicle to solely tap that ESS battery it would get routed to both batteries, meaning ESS events would run on both batteries.

But given your disconnect of the ESS battery in addition to the jumper, ESS events will now only tap your main batteries to run appliances with the engine shut down at a stop lights.

This fact is why it's recommended that you don't run ESS under your new jumpered setup, even if you still had the ESS battery connected.

The whole idea of separating the dual stock batteries in an ESS event was to preserve the main battery for engine cranking. Specifically, once the vehicle terminates the ESS event, either because you've taken your foot off the brake, or the ESS battery voltage has run low, or you've done something that is inconsistent with being in ESS (e.g. put an automatic in a manual gear) both batteries on a stock JL are brought back into parallel to both energize the crank of the engine, the main battery bearing, not taxed in the ESS event, most of the brunt of that work. In your case only the main battery runs an ESS event and then, partially drained from the ESS event, attempts to crank the engine.

In either case, ESS battery connected or not, ESS events with your jumper in place rob the main battery of cranking power: more so in your case given there's only one battery. The vehicle's monitoring of that ESS battery's voltage during ESS events , or so it thinks, to early terminate the ESS event if the ESS battery's voltate runs too low, is really now, because of your wiring change and ESS battery disconnect, just an assessment of the voltage of your main batttery.

(Had you not disconnected the ESS battery the voltage assessment of what the vehicle thinks is the ESS battery in ESS events would have been a composite voltage of both batteries.)

In theory your ESS event could last longer than it should were it only running off the ESS battery (because the main battery has more capacity.) Additionally you could risk not having enough power in the main battery to effect an engine crank once the light turns green because that main battery was drained in the ESS event. So turn ESS off when using a jumper, especially if you are bypassing the ESS battery. How you turn off ESS, buying tech or pushing the ESS off button at crank is all fine by me.

Your jumper and disconnection of the ESS battery does permanently and exactly what TSB 18-092-19 does in factory wiring if after a crank attempt, the Aux battery is dead, but the main battery has enough power to crank on the second and all subsequent cranks.

The difference between the two is that your jumper doesn't automatically turn ESS off while the TSB does if what it "thinks" is the Aux battery (i.e. if you don't change factory wiring) is dead.

So turn ESS off yourself.

(Yes, some vehicles are designed to run ESS with one battery. The JL isn't.)

Thank you!!

Nick:

You correctly got your "no" but there's more to it than that, that you should know. The short version is turn ESS off. The explanation as to why follows:

TSB 18-092-19 affects some changes to the JL inside and outside the realm of the batteries and their logic, but discussion of other than batteries and logic is off topic.

The functionality of TSB 18-092-19, whose logic you seem to appreciate is built into most but the earliest JLs, changes what happens during the vehicle's pre-crank instantaneous isolation and testing of the Aux battery (the same battery you've bypassed,) if said testing shows the battery as dead.

Assuming factory wiring, which you've changed and I'll cover, prior to TSB 18-092-19, you were stranded if your Aux battery was dead. Subsequent to the TSB, while your attempt to crank will still fail if that Aux battery is dead, future attempts to crank after than will be tried by the vehicle solely off of the main battery. If successful, the vehicle will turn ESS off, letting you know as such in the dash. All future engine cranks will happen on the first try, and that ESS off light will not go away until the next crank, if any, where an energized ESS battery (again, based on stock wiring--which you now don't have) is detected.

Your jumper tricks your JL such that calls it thinks it makes (only to) the ESS battery are actually now rerouted to the main battery.

In a stock dual AGM battery JL like yours, the batteries are always connected in parallel but an instant during this pre-crank test, and during ESS events. Jumper the batteries like you did, but don't disconnect the ESS battery (which you DID do) and the two batteries are always in parallel.

Jumper the batteries and disconnect the ESS battery (your direction) and all calls for battery power by the vehicle to any and all batteries always are energized now from solely the main battery.

That said, let's talk about how the installation of your jumper affects things. With its placement and your bypassing of the Aux battery, as stated, all calls to what the vehicle thinks is the Aux battery get channeled to the main battery. That pre-crank test goes against the main battery now. Had you not disconnected the ESS battery with that jumper, nothing the JL could do would isolate that ESS battery, even though it would still be tapped for power. Attempts by the vehicle to solely tap that ESS battery it would get routed to both batteries, meaning ESS events would run on both batteries.

But given your disconnect of the ESS battery in addition to the jumper, ESS events will now only tap your main batteries to run appliances with the engine shut down at a stop lights.

This fact is why it's recommended that you don't run ESS under your new jumpered setup, even if you still had the ESS battery connected.

The whole idea of separating the dual stock batteries in an ESS event was to preserve the main battery for engine cranking. Specifically, once the vehicle terminates the ESS event, either because you've taken your foot off the brake, or the ESS battery voltage has run low, or you've done something that is inconsistent with being in ESS (e.g. put an automatic in a manual gear) both batteries on a stock JL are brought back into parallel to both energize the crank of the engine, the main battery bearing, not taxed in the ESS event, most of the brunt of that work. In your case only the main battery runs an ESS event and then, partially drained from the ESS event, attempts to crank the engine.

In either case, ESS battery connected or not, ESS events with your jumper in place rob the main battery of cranking power: more so in your case given there's only one battery. The vehicle's monitoring of that ESS battery's voltage during ESS events , or so it thinks, to early terminate the ESS event if the ESS battery's voltate runs too low, is really now, because of your wiring change and ESS battery disconnect, just an assessment of the voltage of your main batttery.

(Had you not disconnected the ESS battery the voltage assessment of what the vehicle thinks is the ESS battery in ESS events would have been a composite voltage of both batteries.)

In theory your ESS event could last longer than it should were it only running off the ESS battery (because the main battery has more capacity.) Additionally you could risk not having enough power in the main battery to effect an engine crank once the light turns green because that main battery was drained in the ESS event. So turn ESS off when using a jumper, especially if you are bypassing the ESS battery. How you turn off ESS, buying tech or pushing the ESS off button at crank is all fine by me.

Your jumper and disconnection of the ESS battery does permanently and exactly what TSB 18-092-19 does in factory wiring if after a crank attempt, the Aux battery is dead, but the main battery has enough power to crank on the second and all subsequent cranks.

The difference between the two is that your jumper doesn't automatically turn ESS off while the TSB does if what it "thinks" is the Aux battery (i.e. if you don't change factory wiring) is dead.

So turn ESS off yourself.

(Yes, some vehicles are designed to run ESS with one battery. The JL isn't.)

Thanks for the explanation, I recieved the smart stop start yesterday getting ready to install now!

 

[namodei]

Just saw your post or I would have replied sooner.... Glad you got it worked out.

I have been pretty busy.

In the last 3 days, I have changed out 3 Aux batteries and 3 Main batteries on other peoples JL's. I did manage to get one other guy to just have me do the jumper-less bypass on his JL.

Anyway, I'm sure you will soon be saying to yourself.... Why did I not do an Aux battery bypass sooner..

No worries, so glad I did this bypass i also went with your recommendation and got the smart stop start getting ready to install now!

 

[Crowbar]

@Ratbert

The Tazer JL is a terrific adjunct, but I do not willy-nilly recommend installing one. Truth of the matter most JL/JT owner's are undoubtedly best, not installing a Tazer JL.

-Many here installed a Tazer JL... they used it for awhile and then they ran from it/they sold it..
They did not want the headaches...they did not want the responsibility.. They did not want marry and unmarry and more.

@Cux211 inquired about a "start/stop eliminator" and what one most everyone is using in regard to same..... I gave him an answer. I use a SmartStopStart as many here do .... and I as other's do, highly recommend it.

In closing, I am very pro, the Tazer JL, I am very knowledgeable it regard to the Tazer JL..... but....

.

Can I also change tire sizes, gear ratios, and disconnect in 2wd with the smart stop? Or is it just for stop start?

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