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How to: Disconnect AUX battery and run just off the main with no errors! PICS!

54835 Views 111 Replies 28 Participants Last post by  cbrenthus
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.
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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.

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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.

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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!
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Just means your main is not charging fully. I drove around with my '19 Wrangler doing exactly that for 3 years before it finally died and wouldn't start. The ESS did work for a few days after I took a road trip just a few months before it died completely. AAP testing isn't always that great because they want to tell you that the warrantied battery you got from them is still good ;)

How old is your main? If its over 3 years I'd replace it and be done.
Just means your main is not charging fully. I drove around with my '19 Wrangler doing exactly that for 3 years before it finally died and wouldn't start. The ESS did work for a few days after I took a road trip just a few months before it died completely. AAP testing isn't always that great because they want to tell you that the warrantied battery you got from them is still good ;)

How old is your main? If its over 3 years I'd replace it and be done.
It's only about a year old. It came from the dealer (i.e., it's a Mopar AGM one with 650 CCA) under warranty because the factory one had apparently conked out. In other words, AAP had no incentive for telling me it was good :p
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If I am going to disconnect the negative cable for the aux battery where do I store the cable so it doesn't short to anything or touch the aux negative terminal driving around? Where did you zip tie it to? I don't have electrical tape right now, but I could duct tape it or blue painters tape it.
You can zip tie it out of the way anywhere. As long as it doesn't touch a hot positive, which should all be covered except the PDR, it'll be fine. If the negative touches the vehicles metal, that is already negative so no issues there. ;) But I highly recommend you run out and get electrical tape for piece of mind ;)
@cbrenthus

Much appreciate your article.
I'm now looking for the solution to get rid of both batteries and replace them with one the biggest could have fit new space.
I think the manual for doing this will be the another pinned killer post.
So

Original H6 is about = 11"
Original AUX = 3 7/16"

Overall: 14 7/16"


H7 = 12 7/16”
H8 = 13 15/16"
H9 = 15 1/2"

Looks like H8 can easily fit.
The question still open if there a space gap where plastic tab located between batteries and what's the dimensions of it, so maybe H9 could fit as well if there additional 1 5/8" available.
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So

Original H6 is about = 11"
Original AUX = 3 7/16"

Overall: 14 7/16"


H7 = 12 7/16”
H8 = 13 15/16"
H9 = 15 1/2"

Looks like H8 can easily fit.
The question still open if there a space gap where plastic tab located between batteries and what's the dimensions of it, so maybe H9 could fit as well if there additional 1 5/8" available.
Thought I answered that already, might have been in a different thread. I have an H7 now, and the tab separating the batteries is in the way. The H7 sits at an angle resting atop the tab. One of these days I'll dremel the tab off and let it sit flat. I don't know if the bigger batteries will fit height and width wise though.
Thought I answered that already, might have been in a different thread. I have an H7 now, and the tab separating the batteries is in the way. The H7 sits at an angle resting atop the tab. One of these days I'll dremel the tab off and let it sit flat. I don't know if the bigger batteries will fit height and width wise though.
They all same wise and height but maybe something will actually prevent it to fit.
Please, could you just do the measuring of the full box you'll while the dremeling the tab.
@cbrenthus so I am hitting some problems after I disconnected my aux negative. I guess I could start a new post, but you seem knowledgeable on this topic. First it was just the start/stop disable light, but then a few days later I got a check engine light on. Is that normal since I don't see that info on this forum?

The main battery tested normal 95% CCA at a parts store. I took it to a mechanic and they just reset the codes, but they are saying the check engine light will for sure come back with the aux negative disconnected so I can't tell then when I have a real check engine light problems or if its just from the aux being disconnected... I am on my 4th aux battery averaging 1.5 years between batteries and the three year warranties from autozone supposedly only covers the first battery replacement and if you need a second replacement in the three years you are SOL. We have only used start/stop like 3 events when we forgot to turn it off on start up. I would have thought that would help the aux last 3+ years instead of 1.5 years.

So I am in a rock and hard place. I wanted to just disconnect the aux and be done with buying batteries all the time, but I will have a check engine light and I will fail my yearly car inspection with any codes. I have heard a few people not having an aux for three+ years and being ok. So they don't have car inspections? They don't have check engine lights? Any aux batteries with longer than a 3 year warranty or unlimited replacements in their warranty period?

Autozone said I had these codes:

P0456 Evap system small leak
C006A-54 multi-axis accel sensor
c2222-68 improper powerdown (probably battery disconnect)

Mechanic said I had these codes:
POOFD, B16F8-15, P0456
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@demonVan welcome to the forum! Those codes are not normal, though the POOFD start/stop unavailable will happen if you remove the AUX without disconnecting the PCR. Did you follow the instructions in the first post to disconnect the PCR before disconnecting the AUX battery? If you didn't, please go back to the first post and follow the instructions.

If you did, these would be my next steps:
1. Disconnect main battery negative so that there is no power to the vehicle
2. Confirm vehicle has no power by opening the door, pressing buttons, etc
3. Let it sit without power for at least 5 minutes, and preferably at least an hour
4. Reconnect main battery negative
5. Start and drive and see if codes come back
6. If codes don't come back, then it was some fluke that happened when the battery was disconnected
7. If the codes come back, go back to step 1, but when you get to step 4, connect both batteries.

In my Wrangler with the same system, I once disconnected just the AUX without disconnecting the PCR to see what would happen. I know I got a yellow @ light and start/stop was disabled, but I'm not sure if I got an engine light and codes but I think I did. I know I posted about it on the JL forum, and I also found out that disconnecting both batteries reset the codes.

I also suggest getting a code reader if you are going to be doing any types of mods to newer vehicles. They can be had for $30 and its so much easier than having to have to go to someone.

Lastly, what year/mileage do you have and what state are you in?
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Thanks! Yeah I just removed aux negative instead of doing all the original post steps since I don't have a bunch of tools and was just trying to get a quick fix for the aux batteries dying. It seems like a few forum members just removed the aux negative only.

I think the mechanic disconnected the main battery to reset the codes, but I had to pay $120 diagnostic fee. I was hoping they would be more knowledgeable since I could have just reset the codes myself for free.

2018 Touring L I think with 63K miles. I am in Texas.

After writing up these posts I think C006A-54 and c2222-68 went away since the mechanic didn't see it and the mechanic thought POOFD, B16F8-15 would always be there if the aux is disconnected. I wonder if the P0456 is the real reason why my check engine light went on and that is all I would need to fix to get past yearly state inspections. Hopefully P0456 is a fluke and doesn't come back after the code reset.

Do you have yearly inspections and they don't care you don't have an aux battery?
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Well there you go, disconnecting the AUX without disconnecting the PCR as shown in the original post will create an error(s). I think the P0456 might be unrelated, but that is a very common code that is often simply the gas cap not being tightened.

Inspections won't care about the AUX battery, where I live they only care if you have an engine light on because it means there could be something wrong with the emission system. In some counties in my state they have to put a sniffer in the exhaust to make sure it is within spec.
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