3.6L ESS Battery Diagram

drdriller

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So, if I have a dead aux battery and can’t start my Jeep, how do I bypass the six battery so o can get home? Pretend I’m at the mall after a movie
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So, if I have a dead aux battery and can’t start my Jeep, how do I bypass the six battery so o can get home? Pretend I’m at the mall after a movie
Walk to your passenger front tire. Lie on the ground behind the tire.
Reach up behind the rear facing fender plastic and push it forward so that you can look into this cavity.
Find a 2"x2"x4" box with two battery cables coming from it and one small 2 wire connector.
Unplug the connector.
Now, jump start your jeep and drive home.

The reason that you can't start a JL with a dead aux battery is that when starting, that battery is what drives all the electronics required to start. This is controlled by the ESS Relay (the black box). By simply disconnecting the coil driver for that relay, the aux battery is never disconnected from your main battery, and the electronics stay powered by your jumping vehicle.
 
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Jebiruph

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Walk to your passenger front tire. Lie on the ground behind the tire.
Reach up behind the rear facing fender plastic and push it forward so that you can look into this cavity.
Find a 2"x2"x4" box with two battery cables coming from it and one small 2 wire connector.
Unplug the connector.
Now, jump start your jeep and drive home.

The reason that you can't start a JL with a dead aux battery is that when starting, that battery is what drives all the electronics required to start. This is controlled by the ESS Relay (the black box). By simply disconnecting the coil driver for that relay, the aux battery is never disconnected from your main battery, and the electronics stay powered by your jumping vehicle.
I just came in from trying to find it (no luck) when I saw this post, Thanks for clarifying the location. Went back out and got a pic. I agree that unplugging as you describe accomplishes pretty much the same thing as jumping N1 to N2, especially since you posted previously that you tested it and it works. It prevents the batteries from being isolated and disconnecting the Main battery from any electronics. I'm not sure I agree with your explanation of what's going on, but it still works either way. The only thing I would add is if I could, I would disconnect the Aux battery negative cable from the Main battery negative terminal so the bad Aux battery could not impact trying to start from the Main battery.

ESS Relay (PCR) in the wild.
pcr3.jpg


ESS Relay (PCR) in captivity.
pcr4.jpg
 

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I just came in from trying to find it (no luck) when I saw this post, Thanks for clarifying the location. Went back out and got a pic. I agree that unplugging as you describe accomplishes pretty much the same thing as jumping N1 to N2, especially since you posted previously that you tested it and it works. It prevents the batteries from being isolated and disconnecting the Main battery from any electronics. I'm not sure I agree with your explanation of what's going on, but it still works either way. The only thing I would add is if I could, I would disconnect the Aux battery negative cable from the Main battery negative terminal so the bad Aux battery could not impact trying to start from the Main battery.
I completely agree that removing the Aux battery negative cable would be best practice. And if you have the tools to do it, go for it and make sure to tape it up to secure it from accidentally making contact with any nearby ground.

But, in the context of stuck at a mall parking lot... you should be fine to just pull the relay control. Also, by leaving it connected while driving home, that battery will get a chance to charge up, if it can.
 

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This is why I have this in my glove box

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drdriller

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WranglerMan. Would you go from N1 to N2. Or N1 to N3 if your ees battery died?
 
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Jebiruph

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I completely agree that removing the Aux battery negative cable would be best practice. And if you have the tools to do it, go for it and make sure to tape it up to secure it from accidentally making contact with any nearby ground.

But, in the context of stuck at a mall parking lot... you should be fine to just pull the relay control. Also, by leaving it connected while driving home, that battery will get a chance to charge up, if it can.
By all means if you can do nothing else, unplugging the relay may help, but there is a very limited set of circumstances where just unplugging the relay will improve the situation. If the Aux battery is drained, so is the Main battery because they are connected in parallel. Unplugging the relay will have limited benefit here unless you also disconnect the Aux battery negative, then you only have to charge the Main battery to get going. If just the Aux battery is drained, it means the ESS relay is bad or the ESS fuse is blown, isolating the batteries and preventing just the Aux battery from charging. Unplugging the relay won't help here.

It will help the situation where a bad Aux battery is causing sporadic electronic behavior, as long as the Main battery still has a charge. Even then, disconnecting the Aux battery negative removes any possibility of it impacting starting from the Main battery.

So if you're reading this post and learning about disconnecting the relay to increase your odds of surviving a battery issue, realize that having an adjustable wrench or a pair of pliers in the jeep to disconnect the Aux battery negative increases the odds even more. Or replace the Aux battery negative cable nut with a wing nut, so no tools are needed to disconnect it. And no need to tape or secure the battery ground.
 
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Jebiruph

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By all means if you can do nothing else, unplugging the relay may help, but there is a very limited set of circumstances where just unplugging the relay will improve the situation. If the Aux battery is drained, so is the Main battery because they are connected in parallel. Unplugging the relay will have limited benefit here unless you also disconnect the Aux battery negative, then you only have to charge the Main battery to get going. If just the Aux battery is drained, it means the ESS relay is bad or the ESS fuse is blown, isolating the batteries and preventing just the Aux battery from charging. Unplugging the relay won't help here.

It will help the situation where a bad Aux battery is causing sporadic electronic behavior, as long as the Main battery still has a charge. Even then, disconnecting the Aux battery negative removes any possibility of it impacting starting from the Main battery.

So if you're reading this post and learning about disconnecting the relay to increase your odds of surviving a battery issue, realize that having an adjustable wrench or a pair of pliers in the jeep to disconnect the Aux battery negative increases the odds even more. Or replace the Aux battery negative cable nut with a wing nut, so no tools are needed to disconnect it. And no need to tape or secure the battery ground.
I should point out that the situation where the bad Aux battery causes the sporadic electronic behavior is probably the situation that tends to strand people away from home the most, so knowing how to unplug the relay is good information. The batteries draining seems to happen overnight and not during trips to the mall.
 

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Thanks @Jebiruph for your outstanding diagrams with their explanations, also, thanks to @redracer explaining where the location of the ESS Relay (PCR) is located.


When Jeepinformant’s video first came out on how the Jeep can start with only the AUX battery connected but not only with the starting battery connected; I have been curious how the starting circuits function. I guess I should just push the button and drive the Jeep and not worry myself of what is happing in the background, but it’s not my nature. How/why will the Jeep start with only the AUX battery connected and the starting battery disconnected, but not the opposite battery configuration?

Are the starting and AUX batteries ALWAYS in parallel EXCEPT when the PCR is triggered by the voodoo electronics to isolates them in a start-stop event? I am ASSUMING for a very short duration of time that the PCR isolates the two batteries when the brake pedal is depressed and the start button is pushed to start the Jeep. Just like with ignition keyed vehicles of the past, when the key was turned to the start position, the starter and only critical circuits for starting the engine were supplied voltage, most or all other nonessential engine starting circuits were isolated so the starter would have maximum battery starting capacity.

When only the AUX battery is isolated and the start button is pushed, and IF the PCR contacts momentarily opens, there will not be any supplied voltage to N1 preventing the start sequence to complete or maybe even initiate.

When the only the starting battery is isolated, N1 will have supplied voltage from the AUX battery, but N2 and the starter will be isolated from power IF my assumption is correct that the PCR momentarily opens when the start button is pushed. So, for the Jeep to start with only the AUX battery supplying power, the PCR must close again during the starting sequence suppling power to N3 (150 amp fused) that is also suppling power to the busbar that is the same as N2 and the starter.

This is just a guess how this crap works.
 

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Has anyone disabled ESS with a Tazer and then removed the AUX battery?
 

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Has anyone disabled ESS with a Tazer and then removed the AUX battery?
@cbrenthus

There are those that have bypassed the Aux battery and left ESS alone lets say.

Also those that bypassed the Aux battery and then disabled ESS with a SmartStopStart or a Tazer JL.

I believe all that have done the aforementioned, did this for a short time only.... just to see....

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mazeppa

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Has anyone disabled ESS with a Tazer and then removed the AUX battery?

I have the ESS disabled with the SmartStopStart and have a fused jumper strap at ready for the N1-N2 terminals. If I had to pay to replace AUX battery out of my pocket, I would remove the PCR and AUX battery from the circuit and continue to use the SmartStopStart to keep the ESS disabled.

It is a shame Jeep had to add this additional cost and complexity of the ESS to the JL 3.6, it could be worse, think about the additional upcoming complexity issues awaiting the 2.0L turbos. (damn I almost ordered a 2.0L)
 

Jeep 5150 2112

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I can verify that it will allow both batteries drain dead. I came out one morning to find only 7v on BOTH batteries.

I was able to charge them for about 30min, then I jumped the main battery to another vehicle to get it to start.

They both charge together and drain together. It truly looks like the only time that they are separate is when you press the START button ... or possibly when ESS is active.
How did you charge both batteries? I was always told to disconnect the the terminals from the battery and just charge the battery directly. Otherwise there's a possibility damaging electrical system or taxing it heavily.
 

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How did you charge both batteries? I was always told to disconnect the the terminals from the battery and just charge the battery directly. Otherwise there's a possibility damaging electrical system or taxing it heavily.

Same as you would charge/jump any other vehicle with a low battery(s); the two batteries are always in parallel except when the PCR isolates them (which is not the case when the Jeep will not start.) This method will charge both batteries at the same time, even though they are different size and capacity.
 
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