Jumperless Aux Battery Bypass

[Heimkehr]

I know the TSB says not to remove the wire connection, but I found that doing that reset the ISB. If you buy a new one, it has just been in a box, so I figured that’s the best way, and it worked for me

I had to disconnect the whole shebang when I replaced the main battery and isolated the ESS battery, to no ill effect when the remaining cables, and IBS, were reconnected.

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[sjones87]

Hey all, I disconnected f42 and taped off the aux battery cable last March. Also installed a brand new Odyssey Performance Battery at the same time. Everythings been running smooth til last week.

Last Monday, I had to jumpstart the Jeep after running into the grocery store. Then on Saturday, I had to jump start it again after parking for a few hours.

The battery still has juice based on my readings. Now out of nowhere while sitting at a red light, my 7 inch screen is glitching and has lines all over the screen.

Should I look into getting a new screen? Or does anyone think this may be the result of something going wrong with the battery? I have the aux disconnected but should I maybe just hook it back up and install a new aux battery?

 

[Heimkehr]

@sjones87

I'll jump to Step 2 by suggesting that you examine the CANBUS blocks behind the glovebox door (which will need to be removed to gain access to said blocks.)

Wiggle each individual connector while the engine is running. If any one of them causes the head unit's screen to visibly glitch, or cause any other odd outcomes, consider replacing both blocks. They are known to be the source of seemingly unrelated electrical issues, such as what you've been experiencing.

Step 1 was to suggest load testing the battery twice: Once to determine resting voltage, which should be no less than 12.3V after sitting overnight, and once during a cranking event. The resting voltage can be fine, and then fall off a cliff when starting the engine. If that occurs, battery replacement may be indicated.

Best of luck with the resolution process.

 

[Mguy]

@sjones87
Step 1 was to suggest load testing[?] the battery twice: Once to determine resting voltage, which should be no less than 12.3V[?] after sitting overnight, and once during a cranking event. The resting voltage can be fine, and then fall off a cliff when starting the engine. [?] If that occurs, battery replacement may be indicated.[?]

Blue question marks are mine in the above quote.

See post #6 here, and any number of manufacturer's websites that show charts for the correlation between an AGM's resting (open circuit) voltage and the battery's estimated state of charge (SOC).

 

[THAW]

FYI, user intervention isn't required for a 2-4 hour quiescent phase of not more than 500mA discharge (note Star Case document language "if unsure of quiescent state current"). It's essentially guaranteed to occur during the first significant vehicle-off period unless one has a consistent aftermarket parasitic draw.

Also, JScan users can view IBS Quiescent Current (Body Control Module Live data).

The Star Case shouldn't be read as indication resetting the IBS is necessary or beneficial outside of a significant battery issue requiring charging/replacement (for which relearn happens by default); it's meant to prevent unnecessary replacement of an IBS due to misunderstanding of IBS functionality and/or misdiagnosis of battery issues.

The first thing @WashingtonWetWheeler should do is try charging the battery. In fact, it's best for IBS relearn to occur on a charged battery, anyway (as alluded to in the Star Case).

 

[Mguy]

FYI, user intervention isn't required for a 2-4 hour quiescent phase of not more than 500mA discharge (note Star Case document language "if unsure of quiescent state current"). It's essentially guaranteed to occur during the first significant vehicle-off period unless one has a consistent aftermarket parasitic draw.

Also, JScan users can view IBS Quiescent Current (Body Control Module Live data).

The Star Case shouldn't be read as indication resetting the IBS is necessary or beneficial outside of a significant battery issue requiring charging/replacement (for which relearn happens by default); it's meant to prevent unnecessary replacement of an IBS due to misunderstanding of IBS functionality and/or misdiagnosis of battery issues.

The first thing @WashingtonWetWheeler should do is try charging the battery. In fact, it's best for IBS relearn to occur on a charged battery, anyway (as alluded to in the Star Case).

Interesting stuff, but the advice for @WashingtonWetWheeler was already given in post #836. All battery load testing presumes a fully charged battery.

 

[WashingtonWetWheeler]

So after pulling my negative terminals off the battery and letting it sit for 2 hours+. I then reconnect and drive per normal? I read something earlier about a certain amount of consistent days of use for it work???

 

[Y2KFirehawk]

Having read through this thread in entirely, it is this level of technical detail and content that keeps me loving forums. Thank you all! Did the Fuse 42 and negative disconnect on my '19 JLU, may consider getting rid of the entire system as outlined here at some point.

 

[ScotM]

Having read through this thread in entirely, it is this level of technical detail and content that keeps me loving forums. Thank you all! Did the Fuse 42 and negative disconnect on my '19 JLU, may consider getting rid of the entire system as outlined here at some point.

I did remove the entire system, so feel free to reach out at anytime.

 

[Ragincajun]

So pulled the fuse and disconnected the Aux battery. When I went to start it everything started kind of flashing on and off. It would not start.

 

[Jebiruph]

So pulled the fuse and disconnected the Aux battery. When I went to start it everything started kind of flashing on and off. It would not start.

That's typically an indication that your main battery is too weak to power a start without the help from the aux battery.

 

[AndySpill]

So pulled the fuse and disconnected the Aux battery. When I went to start it everything started kind of flashing on and off. It would not start.

If you pulled the wrong fuse (its 42) AND you have an early model 2018 that hasn't been flashed with TSB 18-092-19 this could also cause what you experienced.

Early 2018's need to see an Aux battery with power at start up, or (by pulling Fuse 42) be tricked into thinking that they are seeing an Aux battery with power when pulling Fuse 42 causes that power request to be redirected to the main battery.

Of course if the main battery's dead: see Jebiruph's prior post.

 

[gm920]

So pulled the fuse and disconnected the Aux battery. When I went to start it everything started kind of flashing on and off. It would not start.

Sounds like you need a software/firmware update. ESS logic was change in 2019 to check and store condition of the AUX battery only once. If the AUX is low/bad/missing the Jeep will start on the second press of the start button and ESS is locked out. You will have to reconnect the AUX and clear any stored codes, then your Jeep should start.

 

[Ragincajun]

Hooked it all backup with a fresh main and all is well. Going to get the TSB and then redo the aux delete.

 

[Y2KFirehawk]

Perhaps written somewhere in the 57 pages, but I'll restate if it helps others. My 19 was reporting to service start/stop but kept it disabled, which was nice. I did the disconnect here and the service message continued. I disconnected the main battery for 10 minutes, reconnected and the ESS message ceased and the functionality resumed. I then purchased the eliminator from https://www.autostopeliminator.com/ and all is good in the world

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