EDIT: I want to be clear that this does not disable ESS. Simply disconnecting the AUX battery will disable ESS, but that will throw an error. Doing the following has no affect on ESS, it will continue to work as normal, just off the main battery
. If you want to disable ESS, that is a different subject.
ANOTHER EDIT: Please seat your fuses- open your fuse block and simply press down on every fuse, you'll be surprised how many click into place. This has been reported to solve many gremlins, and the 90 seconds it takes is worth ruling it out
I have both a wrangler and pacifica running the same dual battery system with ESS. I don't like ESS and disable it every time, and installed a smart start stop on the pacifica so its always disabled. I also really don't like the dual battery setup - I understand the idea behind it but the engineers really messed up when they decided to leave the batteries in parallel when the engine is off, thus a bad battery takes them both down. I also wonder if the AUX batteries get overcharged due to being charged as long as the main is being charged, thus causing them to fail prematurely.
So, a quick overview of the dual battery system on your pacfica: The main battery is used for starting the engine, and the aux battery is used for running the electronics when the ESS shuts off the engine during a stop. By doing so, it preserves your main battery to start the engine back up, something that's pretty important when in traffic. The part that separates the batteries is the Power Control Relay (PCR). When you press the start button, the computer sends a signal to the PCR to separate the batteries, and then checks the voltage to ensure that the AUX battery has voltage to power everything during an ESS stop. This AUX voltage check takes 1/10 of a second or less, so you don't notice it, but if the computer doesn't get full voltage, it disables ESS and you get an error message. This is why simply disconnecting the AUX battery doesn't really work - you'll get an error message every time you start. If this doesn't bother you, than go for it and it will also disable ESS (I ran my wrangler like this for a few months). Although, if you go this route, and wish to reconnect the AUX, you will need to disconnect both batteries for a few minutes first to erase the error, or use a code reader to clear it.
So, to not receive the error, you need to disconnect the PCR. What we are doing here is removing the signal wire that tells the PCR to separate the batteries. Now, when the computer tells the PCR to separate the batteries, the PCR doesn't get the message, leaves both batteries connected, and that is the voltage the computer reads. With the PCR unplugged and the AUX disconnected, the computer is reading the voltage from the main battery when it thinks it is reading from the AUX.
Now that you understand how the system works and what we are doing to bypass it, lets get started:
Open the hood and remove the airbox connector to service the batteries. To remove the airbox, refer to the picture below for the screw / bolts needed (each one is circled in yellow). The airbox cover might be 8MM and not 10MM, I can't remember. The PCR that needs to be unplugged is circled in red. If you have small hands or a really talented you might be able to unplug the PCR without removing the airbox, but it only takes a few minutes and gives you much more room.
View attachment 44531
Now that everything is removed, you can easily access the PCR. You want to unplug the signal wire shown below. To do so you need to pop the gray tab out, then squeeze the connector as you pull it off. DO NOT FORCE IT!!! You don't want to break this. It can be a bit difficult, but not overly so.
See below, and while I think the posts I labeled as "don't touch" are negatives so it should be fine, its best not to touch them anyway.
EDIT: I was reviewing a wiring diagram and it looks like these are actually positive, so absolutely don't touch them (or disconnect both batteries before doing this procedure, which is a good idea anyway). I'm not impressed that FCA didn't make these red and/or cover them.
View attachment 44532
Now all you have to do is disconnect the negative from the AUX battery, wrap it in electrical tape to be safe, and you are done. I zip tied mine down to keep it out of the way.
View attachment 44533
Then put the airbox back together and you are good to go, running on a single battery the way it should be
Just remember to put it all back if you go to the dealer for anything!