Jumperless Aux Battery Bypass

[AndySpill]

With his diesel you just take out the main and pull out the aux from underneath it. No need to mess with fender liners.

Thanks John; I'll bet you've forgotten more about the specifics of the Diesel than I know.

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[JeepinPete]

I started having cold start misfire/stumble a few weeks back when it first got cold. My aux battery had been dead for a long time and the main battery voltage was low before starting. Figured it was time to replace the main.

Picked up a H7 AC Delco from Amazon. Ended up pulling the aux through the fender well, but in the end I shouldn't have bothered. I do not like the idea of heavy battery leads laying unconnected, even if wrapped, and I did not want to leave the old aux battery installed. So I removed the aux negative lead entirely and rerouted the positive back to the main battery lug. This required pulling the fuse block and tray to get the leads up to the top, so I could have just pulled the aux battery through the top while I was at it.

The procedure when exactly as described in this thread. First push of the starter button did nothing, second push and the Jeep fired right up. ESS works again which is fine by me. Works really well with a 6 speed IMO.

Fortunately the battery replacement took care of the cold start misfire/stumble.

 

[Ratbert]

Thanks John; I'll bet you've forgotten more about the specifics of the Diesel than I know.

Surprisingly I know very little about these beasts. My mind was blown when I found out they don't have engine braking!

 

[Mguy]

The removal or blowing or Fuse 42--either one--prevents isolation of the batteries and is a remedy here. Replacing Fuse 42, either because it has been previously disconnected or blown can only be counter to remedying the questioner's desire to remove the Aux battery , unless they desire the vehicle to shut off ESS with an EVIC warning light (late model dual AGM battery 2018's or later) or fused jumper terminals N1 and N2 in the PDC: the original technique before its inventor @Jebiruph discovered and published the Fuse 42 pull.

Perhaps I misunderstand your advice.

I have no issue with your method of insulating the disconnected cable.

Disconnecting the aux battery negative is all that is required to electrically isolate ("delete," "bypass") the aux battery. At least some JLs then experience ESS disabling with the dash warning illuminated. Opening the PCR control circuit at F42 (before disconnecting the aux battery negative) keeps ESS operational, and manual shutoff on the dash remains available.

Inserting a blown fuse in the F42 socket is electrically identical to removing an intact fuse. But neither has much effect on "stock" operation (when the aux battery's negative is reconnected) because the load circuit at the PCR is normally closed.

 

[AndySpill]

Disconnecting the aux battery negative is all that is required to electrically isolate ("delete," "bypass") the aux battery. At least some JLs then experience ESS disabling with the dash warning illuminated. Opening the PCR control circuit at F42 (before disconnecting the aux battery negative) keeps ESS operational, and manual shutoff on the dash remains available.

Inserting a blown fuse in the F42 socket is electrically identical to removing an intact fuse. But neither has much effect on "stock" operation (when the aux battery's negative is reconnected) because the load circuit at the PCR is normally closed.

Now I get it. You're not suggested to replace a blown Fuse 42 with a working one. You're suggesting to pull Fuse 42 or replace it WITH a blown one.

 

[AndySpill]

I started having cold start misfire/stumble a few weeks back when it first got cold. My aux battery had been dead for a long time and the main battery voltage was low before starting. Figured it was time to replace the main.

Picked up a H7 AC Delco from Amazon. Ended up pulling the aux through the fender well, but in the end I shouldn't have bothered. I do not like the idea of heavy battery leads laying unconnected, even if wrapped, and I did not want to leave the old aux battery installed. So I removed the aux negative lead entirely and rerouted the positive back to the main battery lug. This required pulling the fuse block and tray to get the leads up to the top, so I could have just pulled the aux battery through the top while I was at it.

The procedure when exactly as described in this thread. First push of the starter button did nothing, second push and the Jeep fired right up. ESS works again which is fine by me. Works really well with a 6 speed IMO.

Fortunately the battery replacement took care of the cold start misfire/stumble.

You lost me Pete.

If the first push of the engine starter failed that sounds like you didn't pull Fuse 42 or put a fused jumper between points N1 and N2 on the PDC, but did disconnect the Aux battery, on upon first crank attempt the JL found no ESS battery, used exclusively and successfully the main battery on your second crank attempt and all cranks thereafter, and turned ON the ESS off light in the EVIC (i.e. dash.)

But ESS works again?

 

[gahammerle]

I started having cold start misfire/stumble a few weeks back when it first got cold. My aux battery had been dead for a long time and the main battery voltage was low before starting. Figured it was time to replace the main.

Picked up a H7 AC Delco from Amazon. Ended up pulling the aux through the fender well, but in the end I shouldn't have bothered. I do not like the idea of heavy battery leads laying unconnected, even if wrapped, and I did not want to leave the old aux battery installed. So I removed the aux negative lead entirely and rerouted the positive back to the main battery lug. This required pulling the fuse block and tray to get the leads up to the top, so I could have just pulled the aux battery through the top while I was at it.

The procedure when exactly as described in this thread. First push of the starter button did nothing, second push and the Jeep fired right up. ESS works again which is fine by me. Works really well with a 6 speed IMO.

Fortunately the battery replacement took care of the cold start misfire/stumble.

What codes did you get? Shortly after the cold weather arrived, I've been getting P0303 (misfire cylinder 3) & P0203 (injector circuit cylinder 3). I wonder if my main battery is weak. My aux has been out of the loop for maybe a year.

 

[joliett]

Why do you think the notice is not correct? Looks correct to me. Maybe trouble with #3 injector. I think usual troubleshooting technique would be to switch injectors 3 with another easy to remove injector. If code changes to the injector you switched from , than bad injector.

 

[JeepinPete]

My Jeep set a P0300 if I remember correctly. On cold start it would stumble and misfire for no more than 5 seconds then clear up. Ran fine otherwise. Have not had the problem since the battery replacement. Yesterday was 10* for the morning commute so I think the problem is licked.

Check out post #22. It describes exactly how my process worked. You would not know anything was changed at this point.

 

[joliett]

I did the radio reset twice and the speakers still makes a popping sound on occasion when the engine restarts at a stoplight. I recently updated to the newest version of Uconnect so I wonder if it has anything to do with that? In any event, I’ll keep trying to remember to press the ESS shutoff button after starting.

My dealer did that uconnect update, which I really didn't want... The result was that popping sound. I did the reset myself and the popping sound disappeared completely. If it's not working for you, bring it to the dealer. Or, trust the process.

 

[rirealtor]

Adding to the discussion. I own an Early 2018 JL unsure if it has the TSB. Many months ago the aux battery had message of low power/need replacement and I had not found this board. Just did a YouTube search and found the hood pin disconnect, but it did leave an error message on dash. Fine, we will live w it.
Fast forward a few months and start to get Aux switches charging messages and some others. Stalled once; called AAA and they said battery was fine ( doubtful!) Battery charge constantly reading 14+ on vehicle. This past cold weekend no start. 11.5v w meter on terminals.
Discovered this forum and found the jumper less bypass. Completed the bypass and installed new H7 main. Now at 12.7 constant.
Here are my questions:
Is the hood pin disconnect the same as F42 removal?
By still leaving the secondary ground wire intact for 6 months or so, did this essentially leave the loop open, slowly drawing from main battery? At no time does the ESS work since removal of the hood pin switch.
Now that fuse and wire are removed, still have the the Avenger on the dash and “Service Start Stop”, even after a new battery. But no ESS. Should I order a StartStop to clear this or see if code clears on its on or just live with it?

 

[stingGreyNJ]

DO THIS!!!!

I just came to say, if anybody is worrying about doing this to do it. Having a dead battery but also having no ability to jump start your car is a position that no car owner should be in. I did the fix to disconnect the aux battery and have never looked back. My 2018 JL has had no battery related issues since doing this fix a few years ago.

Just do it.

 

[sweet88gt]

So back on 12-14-23 I was dealing with my second round of Aux battery issues. I bypassed and bought a new main battery.
Today on the start up to come home from work I get AUX switches not available battery charging.

I bypassed by unhooking neg terminal. Tape it off and zip tie it up. Pull fuse.
No issues from 12-14-23 until today. What am I missing ?

 

[OldGuyNewJeep]

So back on 12-14-23 I was dealing with my second round of Aux battery issues. I bypassed and bought a new main battery.
Today on the start up to come home from work I get AUX switches not available battery charging.

I bypassed by unhooking neg terminal. Tape it off and zip tie it up. Pull fuse.
No issues from 12-14-23 until today. What am I missing ?

That’s almost 8 weeks, and these things have parasitic draw. Need to put a charger/maintainer on there at least every other week unless you do serious commuting. Noco-10 or better. Anything less than 7a will do more harm than good.

 

[sweet88gt]

That’s almost 8 weeks, and these things have parasitic draw. Need to put a charger/maintainer on there at least every other week unless you do serious commuting. Noco-10 or better. Anything less than 7a will do more harm than good.

I first thought Tazer but its crazy.
Yes I only drive 14 miles per day. Its a 2020 with 28,000 on it. Really though not driving it more is an issue ? 5 days a week 14 miles per day or so ? Plus my wife will drive it say 4-5 miles every so often.

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