Jumperless Aux Battery Bypass

[Rhinebeck01]

I have a 2018 JLU. Should the remove fuse 42 and aux negative cable work to bypass the small starting battery on my year Jeep?

@wheels082

I have a 2018 JL, that was manufactured on 5/5/18 and the N1-N2, 40 amp fused bypass jumper worked well before and after, TSB 18-092-19 (Power Control Update) that changed the dual battery behavior on my 2018 JL. Been using a 40 amp fused bypass jumper for 4 yrs. and 69,000+.

Also works is.... N1 to Main positive 40 amp fused bypass jumper.

As for the "jumperless bypass" approach, I have not tried that and many here, thanks to posts made that were never followed up on, have muddied the water so to speak in regard to this jumperless bypass thing..

Some posts have left some here wondering is a 2018 JL has not had TSB 18-092-19 performed, not be able to do this jumperless bypass thing....

Anyway, to you, @wheels082 ..... Do try removing F42 and disconnecting and isolating the Aux neg cable that is attached to your Main's neg cable (it's the smaller of the two cables. For your 2018, probably the closest cable to you if you are leaning in over the passenger side fender).

Do the fuse pull and disconnect and isolation of the cable and then go to start your JL. IF your 2018 JL starts right up and no EVIC reports then you know the deed was accomplished..

IF, if you see the JL not starting with single button push, EVIC message then obviously it was a no go. So, just replace the F42 and reconnect the cable and you are back where you were. Any EVIC message that remains will go off after a / a few engine on and offs.

IF the jumperless approach does not work (it very well will) then just do the simple, 40amp fused bypass jumper between N1 and N2 along with the Aux neg cable disconnect mentioned earlier.

Do lets us know here how you make out. Only takes say 10 min. to try and no animals can be harmed during testing..

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[wheels082]

I am not sure of the build date, but my Jeep was purchased in July 2018. I disconnected the negative cable to the auxiliary battery. The Jeep started the second time I pushed the start button and first time every other time I tried. I then removed fuse 42. Jeep starts every time. It now displays service start/stop system message and has a yellow circle with an A and exclamation mark on the dash. I installed the fuse, hooked the negative cable back up and the errors are still there. I tried starting and stopping the engine at least a dozen times. Errors are still there.

 

[Craigzjeep]

2019 JLUR with the 3.6.
Thought I'd rather deal with this now in the garage before the "lawn mower battery" goes south and leaves me stranded.
I Pulled F42 and removed the negative battery cable that goes to the small battery.
Really about a 10 minute job.
I've since put a few hundred miles on it, no error lights .
Success.

 

[Jebiruph]

I am not sure of the build date, but my Jeep was purchased in July 2018. I disconnected the negative cable to the auxiliary battery. The Jeep started the second time I pushed the start button and first time every other time I tried. I then removed fuse 42. Jeep starts every time. It now displays service start/stop system message and has a yellow circle with an A and exclamation mark on the dash. I installed the fuse, hooked the negative cable back up and the errors are still there. I tried starting and stopping the engine at least a dozen times. Errors are still there.

The batteries are briefly separated and the aux battery gets tested every cold start. When you disconnected the aux battery, it failed the test, disabling ESS and turning on the error light. I've always had to disconnect both batteries to clear the error light.

Pulling fuse 42 prevents the batteries from being separated for the aux battery test.

 

[stingGreyNJ]

So car wouldnt start. And i couldnt jump it either a few days ago. Display would say 0V or 14V and everything in between.

found this thread. Pulled negative connectionat main battery terminal (the skinnier wire and its closer to passenger side).
Pulled 42.

So now a jump start should work?

Batts are 5 years old iirc, main battery certainly is so it may be cooked anyway.

I’m just hoping it can start so i can go buy a battery.

 

[mdkautzman]

So car wouldnt start. And i couldnt jump it either a few days ago. Display would say 0V or 14V and everything in between.

found this thread. Pulled negative connectionat main battery terminal (the skinnier wire and its closer to passenger side).
Pulled 42.

So now a jump start should work?

Batts are 5 years old iirc, main battery certainly is so it may be cooked anyway.

I’m just hoping it can start so i can go buy a battery.

Good luck. Report back how it all turns out.

 

[stingGreyNJ]

So car wouldn't start. And I couldn't jump it either a few days ago. Display would say 0V or 14V and everything in between.

found this thread. Pulled negative connection at main battery terminal (the skinnier wire and its closer to passenger side).
Pulled 42.

So now a jump start should work?

Batts are 5 years old iirc, main battery certainly is so it may be cooked anyway.

I’m just hoping it can start so I can go buy a battery.

Good luck. Report back how it all turns out.

Thanks for the interest. I was able to Jump start after aux batt disconnect and fuse 42 pull.

Still, I didn't want to drive it so I drove to get a new main battery, swapped it and drove old battery back for core rebate.

All seems well and going 5+ years on my original 2 batteries is reasonable. What isn't reasonable is not being able to jump start a car in the usual way. That is an oversite IMO.

Jeep was ordered before JLs were being delivered and was delivered in early July 2018 so probably a May or June build date. (I can look if anybody cares) I don't know if I had the TSB done that would affect this hack but all is well for right now.

 

[WrangleDangle]

That message doesn't have anything to do with the aux battery, it's based on the battery sensor's analysis of the main battery. It means that either the main battery is low on charge or the battery sensor needs reset.

How does one reset the battery sensor? Where is the sensor located?

 

[Rhinebeck01]

How does one reset the battery sensor? Where is the sensor located?

@WrangleDangle

Read here:
https://www.jlwranglerforums.com/forum/threads/ibs-clear-reset.67955/

IBS sensor is found on the Neg side of the Main battery.. It's the black piece in this pic.

 

[WrangleDangle]

Thank you very much. I seem to remember seeing your name as one of the experts on these battery issues. I appreciate your help. One last question, does It matter that I disconnected the aux negative cable on the battery before I pulled the fuse. Any problem with that? Thanks again.

 

[Rhinebeck01]

Thank you very much. I seem to remember seeing your name as one of the experts on these battery issues. I appreciate your help. One last question, does It matter that I disconnected the aux negative cable on the battery before I pulled the fuse. Any problem with that? Thanks again.

@WrangleDangle

Vehicle was turned off... No, does not matter which you do first..

 

[WrangleDangle]

@WrangleDangle

Vehicle was turned off... No, does not matter which you do first..

Thank You

 

[JL18]

I have an 2018 JLU Sahara, manufacture date 1/18. I got the “start/stop in battery protect mode” message the other day. I did some poking around and discovered my main battery was around 11.5 volts and my aux was around 12.5 volts. I disconnected the aux. battery negative from the main battery and the Jeep wouldn’t start, main battery was too weak. I reconnected the aux negative and it started back up. Long story short, my aux battery is what was giving the Jeep the extra power to start. My aux battery was replaced by Jeep about 2 years ago while still under warranty and the main was original. I put a battery tester on them and the main tested bad and the aux was still good.
I also noticed the voltage meter on the Jeep was constantly around 14.1 volts when the Jeep was running. I guess it was trying to always charge my bad main battery.
I bought a new main battery and installed with the aux still connected. Now when I first start driving it is around 14 volts. As it charges, the voltage will vary from 12.8 to 14.1 volts, as I believe it is designed to do. At first it starts around 14.1 and gets lower and lower the longer you drive, and it charges, eventually getting to 12.8 volts. When you take your foot off the gas the voltage goes up, charging more when you aren’t using engine power. When you push the gas pedal down the voltage drops down. This is a gas saving measure Implemented on new cars. It usually takes 40-60 minutes of driving before mine gets as low as 12.8, which to me indicates batteries are fully charged.

I also have just decided to install the $50 auto stop/start disable from Amazon.
FURYENGRAVER Plug Play Engine... https://www.amazon.com/dp/B08YN5S713?ref=ppx_pop_mob_ap_share
It was easy to install and seems to work with no problems. It automatically disables auto start/stop every time you start the Jeep. If you push the start stop button, it will still work, Basically it makes the Jeep default to auto stop/start disabled, which is what I like.

After two days of the auto stop/start working with no issues, I decided to try the F42 fuse removal along with disconnecting the aux battery negative cable from the main battery. Everything is working perfectly. No error codes, no having to push the auto start/stop button every time I start the Jeep, no aux battery issues to worry about.

??

 

[NewJLU2019]

I have a question. If you have the Z Automotive Tazer and it keeps the SS turned off full time, then will all the Aux battery issues go away?

 

[JL18]

I have a question. If you have the Z Automotive Tazer and it keeps the SS turned off full time, then will all the Aux battery issues go away?

Don’t think so. The taser is just “pressing the ESS button” for you.

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