3.6L ESS Aux Battery Bypass

[Jebiruph]

@Jebiruph are you gettig any messages displayed in the EVIC telling you that you have a problem with ESS or any other weird messages ?

From my understanding the voltage is not supposed to run 14+ all the time as it may indicate a battery going bad or did you disconnect the IBS relay so it constantly has the alternator charging

No messages or problems indicated, just don't think it should be 14.7v all the time. The constant 14.7v is as is from the factory, no changes to the electrical system.

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[Jebiruph]

You know.. I had a thought about this, this morning...

Why not just disconnect the aux - lead, and unplug the control wire harness from the aux battery relay (forget the name). If it works the way that we think it does, then posts 1 & 3 will stay jumpered because the relay will never be energized... and it looks factory!

Good point. Unplugging the PCR is pretty much the same as installing the jumper, except that the jumper would additionally bypass a bad PCR or blown high capacity ESS fuse. The advantage of unplugging is no extra parts needed. so if you are stranded by a bad Aux battery causing dysfunctional electronics, unplugging the small plug from the PCR is definitely worth trying.

 

[WranglerMan]

No messages or problems indicated, just don't think it should be 14.7v all the time. The constant 14.7v is as is from the factory, no changes to the electrical system.

When I first got my JL the voltage at idle was 12.7-13.0 and was pretty much the same running down the road but on deceleration either by braking or just letting off the gas the voltage would spike up to over 14+ and once stopped would drop back down to the high 12’s but then over several months slowly crept up to 14+ and after I removed my Tazer ESS never worked as it said battery charging and said that for a few months in the EVIC on menu #6 so I took it in and the dealer advised the main battery was bad and once replaced my voltage dropped back down and ESS is again working so with your bypass installed does ESS work and if so are the aux functions while stopped supplied power from the main battery, is so that’s a darn fine invention that would be great or have

 

[Jebiruph]

I think many are underestimating the technology behind the ESS and the-Aux battery. There is I believe another factor at play here where the Aux battery is essential. That is the Managed Charge System where the Alternator does not load the drivetrain when not needed. I believe the Aux battery serves some vital ECM management components to ensure consistent voltage and behavior.

Any FCA electrical engineers on the forum?

Not an FCA EE, but variable alternator output or smart alternators have been around for a long time. On the JL, the Powertrain Control Module Gen Sense monitors the load on the alternator and the Gen Field Control controls the alternator output. I think the only impact the ESS/Aux battery has on the alternator is the additional load needed to charge it.

 

[Jebiruph]

When I first got my JL the voltage at idle was 12.7-13.0 and was pretty much the same running down the road but on deceleration either by braking or just letting off the gas the voltage would spike up to over 14+ and once stopped would drop back down to the high 12’s but then over several months slowly crept up to 14+ and after I removed my Tazer ESS never worked as it said battery charging and said that for a few months in the EVIC on menu #6 so I took it in and the dealer advised the main battery was bad and once replaced my voltage dropped back down and ESS is again working so with your bypass installed does ESS work and if so are the aux functions while stopped supplied power from the main battery, is so that’s a darn fine invention that would be great or have

I have a vague memory that on the many hour drive home from the dealer, I checked and the voltage varied just as you described yours did at first. I didn't check again until several weeks ago when people started mentioning problems and I found that it almost always stays at around 14.7v now. With the jumper installed and aux ground cable disconnected, ESS still works with no errors. I almost always hit the switch to disable it, but sometimes forget and it works as intended.

 

[WranglerMan]

I have a vague memory that on the many hour drive home from the dealer, I checked and the voltage varied just as you described yours did at first. I didn't check again until several weeks ago when people started mentioning problems and I found that it almost always stays at around 14.7v now. With the jumper installed and aux ground cable disconnected, ESS still works with no errors. I almost always hit the switch to disable it, but sometimes forget and it works as intended.

So the big question is do you think if you removed the ESS battery and installed your jumper on the N1 and N2 terminals that the JL would start fine and supply the necessary voltage for ESS operation if needed

 

[Hgrace]

Pretty sure the main, larger battery is used for the engine starts and the smaller one is used to keep the cabin equipment operating seamlessly while the engine is stopped and starting.

But of course I don't know for sure.

 

[Jebiruph]

So the big question is do you think if you removed the ESS battery and installed your jumper on the N1 and N2 terminals that the JL would start fine and supply the necessary voltage for ESS operation if needed

Yes, disconnecting the ground cable electrically removes it, physically removing it then is just a formality. As bad as the dual battery system is, I think it is an improvement over the single battery system like in the Cherokee, as long as you are prepared to re-mediate the occasional aux battery anomalies.

 

[HotKarlTheJL]

I understand nothing in this thread. All I know now is it caused me to not trust the Jeep when I go out camping. That really sucks.

 

[Hgrace]

I understand nothing in this thread. All I know now is it caused me to not trust the Jeep when I go out camping. That really sucks.

Get a second deep cycle battery. Be a a marine enclosure. Put it in the back when you're in the wild. Rig a charge lead for it. Use it for your camp power. There are also low cost 600-2000 watt generators that are very compact an efficient with both 120v and 12v outlets.

 

[W1ck3d]

You just need a jumper from n1 to the main battery to bypass... I also disconnect n3 sometimes but i dont believe it is necessary

 

[Jebiruph]

I understand nothing in this thread. All I know now is it caused me to not trust the Jeep when I go out camping. That really sucks.

That's the opposite of what I was trying to accomplish with this thread. Some people are reporting electrical system failures that require a tow to a dealer and then find that the cause was a bad aux battery. I'm trying to show a simple way to bypass the aux battery so it doesn't strand you, to increase confidence to take the Jeep camping.

 

[WranglerMan]

@Jebiruph I for one have really enjoyed following this thread, the time you have taken to not only post your results but to show pics of the bypass needed is greatly appreciated, my skills on the electrical side of anything is very lacking but you have made it pretty easy to understand on what’s needed to get one back on the road if that poorly placed ESS battery craps out

 

[Rubi]

So after a couple months of my voltage reading consistently 14.7 -14.8v, I decided to put the bypass to the test and see if running with the aux battery bypassed would change the running voltage any. 3 days in and it's running 14.4 - 14.5v, not sure if it's making any difference or not. The jumper is attached to N1 and N2 with wing nuts and aux ground is disconnected, PDC cover fits over jumper. I replaced the aux ground cable nut with a wing nut, so if I suspect a problem with the jumper, I can quickly reattach the aux ground cable and pull the jumper fuse to return to normal.

Been following this thread since the beginning. Thanks for all of your work and research. If the ESS was permanently disabled, unplugging the under hood switch, could you permanently and safely install a fused jumper, as you’ve done, between N1 & N2 terminals and permanently remove the aux battery?

 

[WranglerMan]

Been following this thread since the beginning. Thanks for all of your work and research. If the ESS was permanently disabled, unplugging the under hood switch, could you permanently and safely install a fused jumper, as you’ve done, between N1 & N2 terminals and permanently remove the aux battery?

That’s a very good question, I personally would love that if it’s possible, it’s not that I have the second battery it’s the placement of the battery, it’s fairly easy to replace a battery on the side of the road if needed but getting to the ESS one is gonna be a pain and I feel the location of it was poorly thought out

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