3.6L ESS Battery Diagram

[Jebiruph]

What if you were to bypass the PCR completely? Would that make the two batteries act as one battery all the time? Could this be another way to permanently disable ESS without doing any harm and without a warning light?

Also, have you figured out how the system is able to check the status of the aux battery before initiating ESS? Does it open the relay (isolating the aux battery) to measure the battery while driving to see if it has enough power to initiate ESS? Maybe it does it simultaneously when you hit your breaks. It takes a quick check of the aux battery and only initiates ESS if adequate power?

If you bypass the PCR, say by connecting N1 to N2, then the batteries will always act as one battery. You can accomplish the same thing by unplugging the connector that powers the PCR. Neither will disable ESS, it would just prevent the batteries from being separated when ESS auto stops.

My current theory is that the only battery that is monitored is the Main battery. ESS is disabled if the system determines that the Main battery may not be able to power a restart. As long as the system believes it can restart, ESS is enabled and it will auto stop. Once auto stopped, the system can monitor the voltage of the Aux battery and restart if the Aux battery voltage gets to low.

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[WXman]

They replaced my IBS last week and the paperwork says they replaced the aux. battery. My ESS still is dead and I have a "Battery Protection Mode" message on the dash still. I wonder if a bad PCR could cause this?

 

[Torero]

For those who haven't seen it yet, I have another post regarding bypassing the Aux battery using a jumper from N1 to N2 https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/.

Due to doubts I had about how the PCR worked, I went ahead bought one (PN# 56029766AC) for testing. Contrary to what I previously thought, the relay is normally closed, meaning the PCR connects the Main battery and the Aux battery when no power is applied, and seperates them when power is applied (auto stopped). I also now think it is only a relay with no battery control electronics. I was hoping it would be easy to open it up, but it's pretty well sealed with epoxy.

This explains how the batteries are always connected except when auto stopped and how they drain down as a pair. But it doesn't explain the reported situations of dysfunctional system electronics being fixed by replacing a bad Aux battery when the Main is still good. You would expect the power from the good Main battery to over come a weak Aux battery.

The only explanation I can come up with for this behavior is that low voltage from the Aux battery is causing unpredictable signals from the controlling electronics. This sometimes results in the PCR isolating the batteries and preventing power from the good Main battery from reaching some of the electronics. The next time, the batteries stay connected and power from the good Main battery masks any issues with the weak Aux battery.

Here's an updated diagram with a corrected explanation of how the PCR works and some additional information learned since the last diagram.

For those who haven't seen it yet, I have another post regarding bypassing the Aux battery using a jumper from N1 to N2 https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/.

Due to doubts I had about how the PCR worked, I went ahead bought one (PN# 56029766AC) for testing. Contrary to what I previously thought, the relay is normally closed, meaning the PCR connects the Main battery and the Aux battery when no power is applied, and seperates them when power is applied (auto stopped). I also now think it is only a relay with no battery control electronics. I was hoping it would be easy to open it up, but it's pretty well sealed with epoxy.

This explains how the batteries are always connected except when auto stopped and how they drain down as a pair. But it doesn't explain the reported situations of dysfunctional system electronics being fixed by replacing a bad Aux battery when the Main is still good. You would expect the power from the good Main battery to over come a weak Aux battery.

The only explanation I can come up with for this behavior is that low voltage from the Aux battery is causing unpredictable signals from the controlling electronics. This sometimes results in the PCR isolating the batteries and preventing power from the good Main battery from reaching some of the electronics. The next time, the batteries stay connected and power from the good Main battery masks any issues with the weak Aux battery.

Here's an updated diagram with a corrected explanation of how the PCR works and some additional information learned since the last diagram.

one explanation is the your arrow “main battery to power other stuff” doesn’t exist. The main battery only powers directly the high current stuff and everything else is powered “thru” the auxiliary battery. Therefore if the auxiliary battery shortens it doesn’t matter that you have a good main battery. Hum. This makes a lot of sense to me. If I remove the top arrow of the two, all can be explained

 

[Jebiruph]

one explanation is the your arrow “main battery to power other stuff” doesn’t exist. The main battery only powers directly the high current stuff and everything else is powered “thru” the auxiliary battery. Therefore if the auxiliary battery shortens it doesn’t matter that you have a good main battery. Hum. This makes a lot of sense to me. If I remove the top arrow of the two, all can be explained

The way I read the factory schematic, the main battery powers the powertrain control module and not through a high current fuse. I suspect there are other things it powers not through a high current fuse.

Here's a diagram illustrating how power from the batteries is distributed when the batteries are connected. Since the positive terminals of the batteries are connected, both batteries should be powering everything.

If I disconnect the aux battery ground cable (at the main battery negative terminal), the aux battery cannot provide any power. Power from the main battery should still reach everywhere. But the jeep will not crank and the dash lights flash off and on, similar to what is described by some people when the aux battery fails. This condition appears to be cycling the PCR open and closed, but I cannot explain why it behaves this way.

 

[Torero]

The way I read the factory schematic, the main battery powers the powertrain control module and not through a high current fuse. I suspect there are other things it powers not through a high current fuse.

Here's a diagram illustrating how power from the batteries is distributed when the batteries are connected. Since the positive terminals of the batteries are connected, both batteries should be powering everything.

If I disconnect the aux battery ground cable (at the main battery negative terminal), the aux battery cannot provide any power. Power from the main battery should still reach everywhere. But the jeep will not crank and the dash lights flash off and on, similar to what is described by some people when the aux battery fails. This condition appears to be cycling the PCR open and closed, but I cannot explain why it behaves this way.

I agree with all you say, but I still believe that the main battery doesn’t “power other stuff” directly as shown but only thru the PCR which is normally closed. (Main Bat to N2 to N3 to PCR to all other stuff) The PCR gets the signal from the Aux battery thru the PDC relays. When you disconnect the ground from the Aux Bat the relays start cycling on and off.

 

[Jebiruph]

I agree with all you say, but I still believe that the main battery doesn’t “power other stuff” directly as shown but only thru the PCR which is normally closed. (Main Bat to N2 to N3 to PCR to all other stuff) The PCR gets the signal from the Aux battery thru the PDC relays. When you disconnect the ground from the Aux Bat the relays start cycling on and off.

#17 has the factory schematic that shows the main battery powering other stuff, but I don't think that makes any difference here. We seem to agree that disconnecting the aux battery ground causes the PCR (and by implication the controlling relays) to cycle on and off, but why? The operation of the PCR (normally closed) is designed for the main battery to power everything when no power is available from the aux battery. This may be as close as we can get to an explanation, a weak aux battery results in dysfunctional electronics that interfere with starting the vehicle or the running of an already started vehicle.

 

[Jeepmarkjl]

Looks like the Genesis Dual Battery kit for JL is out now. Install instructions coming soon.

 

[VNT]

I put my jeep away for the winter, yanked the main battery, fully charged the aux battery and isolated the cables. left the aux battery in the Jeep, may throw a charge on it from time to time over the winter. Dont understand why they had to bury the dam thing under the main battery.

 

[Torero]

Since I added a supercharger my ESS has been disabled. My next move is to get rid of the Auxiliary Battery. That’s why I’ve been learning from you guys. My understanding so far is that I can link N1 to N2 and pull the aux out.

 

[zb39]

Looks like the Genesis Dual Battery kit for JL is out now. Install instructions coming soon.

I got one at the eastern expo, along with a whole lot of other stuff. Wish my Rubicon would get here.

 

[Jebiruph]

After some additional work with the batteries, I realized there is a better way to isolate the batteries to check the individual voltages. Instead of removing the main battery positive terminal and risking shorting it out, the same thing can be accomplished by removing the aux battery ground cable from the main battery negative terminal. Doing it this way eliminates the risk of shorting anything out.

Here's the aux battery voltage - positive terminal to aux battery ground.

Here's the main battery voltage

 

[Jeepsterfreak]

After some additional work with the batteries, I realized there is a better way to isolate the batteries to check the individual voltages. Instead of removing the main battery positive terminal and risking shorting it out, the same thing can be accomplished by removing the aux battery ground cable from the main battery negative terminal. Doing it this way eliminates the risk of shorting anything out.

Here's the aux battery voltage - positive terminal to aux battery ground.

Here's the main battery voltage

Thanks for the info and pics.

Could you also remove the negative terminal clamp from the main battery to accomplish the same test? To check the Aux battery, voltmeter neg lead on the clamp (after it is removed from main battery). To test the main battery, voltmeter neg lead directly on neg post with clamp removed. Would that give same results?

 

[Jebiruph]

Thanks for the info and pics.

Could you also remove the negative terminal clamp from the main battery to accomplish the same test? To check the Aux battery, voltmeter neg lead on the clamp (after it is removed from main battery). To test the main battery, voltmeter neg lead directly on neg post with clamp removed. Would that give same results?

That will work for isolating the batteries to measure voltage, but you are removing power from the IBS which may reset it, losing accumulated battery history. That may or may not be bad, just be aware it's possible.

Something I found since I posted this is that which ever battery remains connected to the system during the voltage check will read slightly lower due still being connected to the system.

 

[WranglerMan]

If I end up keeping my JL for a lot of years when the aux battery craps out and is no longer covered by warranty I plan on bypassing it and just will use the main and be done

 

[drdriller]

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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