Jumperless Aux Battery Bypass

[Jebiruph]

I put it back to stock and it is back to normal. Had to replace the main battery and didn’t want to spend $125 on an aux battery for the start stop we don’t use, but is what it is. No errors for now…hopefully the aux is healthy enough that it doesn’t drain down the new battery until I get a new aux this week. I’d just deal with the light and not care, but it bothers the old lady lol.

My comment wasn't directed at you, it was a general comment. Not sure what you mean by dealing with the light, but if your Stop/Start error light is on, it can and frequently means that Stop/Start is disabled due to engine issues, even if the engine issues haven't triggered the CEL yet.

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[PsychoTrucker81]

My comment wasn't directed at you, it was a general comment. Not sure what you mean by dealing with the light, but if your Stop/Start error light is on, it can and frequently means that Stop/Start is disabled due to engine issues, even if the engine issues haven't triggered the CEL yet.

It started working again as soon as I hooked the Aux battery back up and put F42 back in.

I get what you’re saying…there are probably a few dozen things that can set it off. I seem to be unfortunate that I am one of the oddities that the bypass just doesn’t work for.

 

[cabnfvr]

Here's a quandary, we got home today from a motorcycle trip and hopped in the Jeep. No start, dead battery. I pulled F42 and disconnected the aux battery negative cable, then started the Jeep with a jump start booster. I figured we'd drive around and let the main battery charge up. Voltage was 14.4 moving to a low of 12.4 at idle. The problem is the Jeep would die when coming to a stop and would not restart without the booster pack. That's not very safe so we took it back home. There is no indication on the dash that the Jeep is unhappy. (Not ESS related. It dies just feet before a full stop. Out of habit the ESS was switched off. 2018 Wrangler Sport, 3.6 w/automatic.)

Why would the Jeep die when stopping? From everything I know the alternator should keep the engine running regardless of battery condition. The main battery is at the local auto store being charged overnight. It checked good but needed charging. I'll install the main battery tomorrow and try again. I sure wish Jeep had just installed software to kill ESS below 11.4 volts instead of the aux battery "solution".

Next update tomorrow evening....

 

[PsychoTrucker81]

Here's a quandary, we got home today from a motorcycle trip and hopped in the Jeep. No start, dead battery. I pulled F42 and disconnected the aux battery negative cable, then started the Jeep with a jump start booster. I figured we'd drive around and let the main battery charge up. Voltage was 14.4 moving to a low of 12.4 at idle. The problem is the Jeep would die when coming to a stop and would not restart without the booster pack. That's not very safe so we took it back home. There is no indication on the dash that the Jeep is unhappy. (Not ESS related. It dies just feet before a full stop. Out of habit the ESS was switched off. 2018 Wrangler Sport, 3.6 w/automatic.)

Why would the Jeep die when stopping? From everything I know the alternator should keep the engine running regardless of battery condition. The main battery is at the local auto store being charged overnight. It checked good but needed charging. I'll install the main battery tomorrow and try again. I sure wish Jeep had just installed software to kill ESS below 11.4 volts instead of the aux battery "solution".

Next update tomorrow evening....

I can tell you that as early as my 1998 Grand Prix GTP, I couldn’t start the car, then pull the battery with the car running. I remember you could do that with any car back in the day, but newer cars you can’t seem to do it anymore. With newer CANBUS vehicles, I have a had a few vehicles from multiple manufacturers that do some wonky s*#t when the batteries go, and it seems to just happen out of the blue. The wife’s 2012 Equinox we had to jump start, and lights and the wipers kept coming on/going off at random until we replaced the battery

 

[21JLURDG]

Why would the Jeep die when stopping?

This is just my guess. If the computer lost power due to the low battery voltage or during the jump start, the computer might have reset. This past weekend I disconnected the battery on a Toyota while servicing it. Afterwards I went for a drive. The first two stops at red lights, the engine shut down. After restarting it the second time, it never again had a problem. I believe the computer just needs to relearn the proper fuel/air mixture and timing.

And as far as needing to use a jump start, it might just have been that the main battery was still weak. If the voltage was very low to start, the alternator might not have been able to charge it properly. That's why we use battery chargers at home.

In effect, I'm suggesting the problem might have been just something very simple.

 

[Vicki Cox]

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.

WOW THANKS

 

[cabnfvr]

Quandary resolved. I too think the main battery voltage was just too low to make the computer happy. New batteries resolved the issue, but I still wish there had been a low voltage warning or some indication that both batteries were going bad. Can't complain though. The Jeep failed to start in our garage with the motorcycle and car sitting there as backup.

FWIW, the aux battery is actually easy to change if you go slow and watch what you are doing. One hour and fifteen minutes including cleaning the trays, covers, etc. And I installed the H7 main, not H6. Thanks to everyone who started threads or responded on the site by providing a ton of useful information regarding the batteries, issues, work arounds, etc.

 

[Mikester86]

Quandary resolved. I too think the main battery voltage was just too low to make the computer happy. New batteries resolved the issue, but I still wish there had been a low voltage warning or some indication that both batteries were going bad. Can't complain though. The Jeep failed to start in our garage with the motorcycle and car sitting there as backup.

FWIW, the aux battery is actually easy to change if you go slow and watch what you are doing. One hour and fifteen minutes including cleaning the trays, covers, etc. And I installed the H7 main, not H6. Thanks to everyone who started threads or responded on the site by providing a ton of useful information regarding the batteries, issues, work arounds, etc.

What method did you use removing the Aux battery?

 

[cabnfvr]

I removed the aux battery from the top. The Way-of-Life YouTube guy had a great tip, place a towel on the roof and flip the hood all the way back. I have a not so great back so it was far easier for me to lean over the fender than remove it and work from the floor.

p.s. I find it easy to just hit the ESS button on startup so I didn't really want to start bypassing things. That said, I'm still grateful for the knowledge on this forum. I have F42 marked on the fuse cover layout pic, just in case.....

 

[OldBlue]

Well, I just did this on my daughter's '22 JLW 2.0L yesterday, first time I've had a chance to get to it with her schedule. Not sure why I got the results I did, but I pulled the #42 fuse, pulled and isolated the aux negative battery cable, installed the Autostop Eliminator, started it up and have the "A!" symbol illuminated on the dash.

Scratching my head over this one, as I've been successful doing this on our other 2 JLUs and they both are still functioning fine. Followed the same process, pulled the same negative battery as my '21, and have the indicator on the dash, and I'm not sure why. The only thing I noticed that was "different" was the small spark when I reattached the main battery negative cable. I'm assuming it was because of the draw from the door being open and the interior light draw. I don't remember that on mine, but I may have just forgotten that as it's been a while since I did this on mine.

 

[Rhinebeck01]

@OldBlue

I would not install an Autostop Eliminator if you gave it to me for free.

The Autostop Eliminator offering is known to hiccup. Why go with that iffy offering when you can buy a SmartStopStart for the same price (a penny more) and know that you have a terrific unit that never ever hiccups... The SmartStopStart also has a smaller footprint.... and sold by forum sponsor @SmartStopStart.com ... who also is a fellow JL owner.

As for the "small spark" that is normal to see.

I'd get the Autostop Eliminator out of the picture, then try again. Assure you definitely have F42 pulled and the correct cable disconnected on the Main's neg terminal.

 

[OldBlue]

@OldBlue

I would not install an Autostop Eliminator if you gave it to me for free.

The Autostop Eliminator offering is known to hiccup. Why go with that iffy offering when you can buy a SmartStopStart for pretty much the same price and know that you have a terrific unit that never ever hiccups... The SmartStopStart also has a smaller footprint.

As for the "small spark" that is normal to see.

I'd get the Autostop Eliminator out of the picture, then try again. Assure you definitely have F42 pulled and the correct cable disconnected on the Main's neg terminal.

Thanks @Rhinebeck01, I appreciate the feedback. I'm fine with the Autostop Eliminator. I used one in my WK2 with no issues, and the one I put in my daughter's JLW was the same one I used in my '21 prior to installing a Tazer, though to eliminate any questions I will pull the one from my wife's JLU (that works) and try it in the '22. I did verify the fuse, and about the only thing I can come up with is I pulled the wrong neg cable, though I pulled the same one I pulled in my '21.

--EDIT--

I just remembered it was a PAIN to hook up the Autostop Eliminator simple because she has the Alpine sound system, and the amp is there under the dash. Makes an absolute PITFA to get to the plug for the module to plug in.

 

[Rhinebeck01]

Thanks @Rhinebeck01, I appreciate the feedback. I'm fine with the Autostop Eliminator. I used one in my WK2 with no issues, and the one I put in my daughter's JLW was the same one I used in my '21 prior to installing a Tazer, though to eliminate any questions I will pull the one from my wife's JLU (that works) and try it in the '22. I did verify the fuse, and about the only thing I can come up with is I pulled the wrong neg cable, though I pulled the same one I pulled in my '21.

@OldBlue

As I mentioned the AutoStopEliminator is known to intermittently hiccup. Why go with a crapola offering when you can get a know to be, non problematic, highly regarded offering for a penny less.

In regard to the Aux negative cable. Look for and disconnect and isolate, the smaller diameter cable on the Main's neg side. Look close and you will see one cable is slightly smaller in diameter. On some JL's, the Aux neg is not in the same location on the Main's neg side as it is with other JL's.

 

[Rhinebeck01]

Snipe:

I just remembered it was a PAIN to hook up the Autostop Eliminator simple because she has the Alpine sound system, and the amp is there under the dash. Makes an absolute PITFA to get to the plug for the module to plug in.

Newer model year JL's have an added metal cross member under there you have to deal with.... is in the way...

With any model year JL/JT ... Yes, getting to and dealing with the security gateway bypass is a pain. To prevent the pain... to have that pain only once, buy and install a security gateway extension cable.

Now, when you go to the dealer, etc. and need to remove the SmartStopStart unit or Tazer JL, etc., all you do is easily do the deed thanks to the extension cable.

You can buy the security gateway extension cable here.. https://www.zautomotive.com/product/z_sgw_ext/

 

[wheels082]

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?

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