Aux battery bypass. Can I run start/stop with H7 main battery?

[Cardamc986]

So I have done the aux battery delete where you disconnect the negative wire from the aux battery to main and pull F47 fuse. I bought a duralast platinum H7 battery. Since these batteries are made for start stop would I be okay to continue using start stop with just this one big battery since I like to use it? I already know it works physically because the whole setup with start stop is working just want to know if it will ruin my new battery.

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[Hop Hunter]

I fully removed my Aux battery, pulled the F42 fuse, disconnected everything including the negative cable up to the main battery terminal. Working just fine for over a month now.

I didn't want to leave the Aux battery connected to anything so its out of the vehicle entirely.

 

[Andy29847]

yes - the stop/start work fine on one battery.

 

[Dp7]

I believe the only purpose for the Aux battery was to prevent high draw items like a vehicle refrigerator from sucking the juice from your starting battery while the ESS shut off the engine at a red light.

The whole system is so poorly designed though, and you blow fuses when either battery needs replacing, leaving you dead in the middle of traffic. I wouldn't use ESS on batteries that are older than 18 months.... And I'd get a 150amp circuit breaker to bypass the N3 fuse.

 

[Lost1wing]

I believe the only purpose for the Aux battery was to prevent high draw items like a vehicle refrigerator from sucking the juice from your starting battery while the ESS shut off the engine at a red light.

The whole system is so poorly designed though, and you blow fuses when either battery needs replacing, leaving you dead in the middle of traffic. I wouldn't use ESS on batteries that are older than 18 months.... And I'd get a 150amp circuit breaker to bypass the N3 fuse.

My original batteries are 4 years old now and my ESS is still working. I have to put a trickle charger on it from time to time, but that's about it.

Blowing fuses is most likely user error. Jumpstarting the wrong way, not isolating cables during charging/testing or during replacement.

Ignoring symptoms will most likely lead to a no start. A battery charging message on all of the time is sign. Ess unavailable and aux switches stopped working is another sign. The alien warning on the dash is the last warning. You can ignore these and expect have a no start or a shut down.

Eliminating the aux battery only prevents a bad aux battery from killing the main battery. Eliminating the aux battery did take away the early warning because the computer is comparing the main battery to itself. Leaving the aux battery installed and looking at the ess page occasionally could help you determine how the batteries are doing. Ess ready, shortly after warm up is a good thing.

 

[Andy29847]

Eliminating the aux battery only prevents a bad aux battery from killing the main battery. Eliminating the aux battery did take away the early warning because the computer is comparing the main battery to itself. Leaving the aux battery installed and looking at the ess page occasionally could help you determine how the batteries are doing. Ess ready, shortly after warm up is a good thing.

I do not believe that the above statement is correct. The computer does not "compare" batteries. The computer checks the state of the aux battery when the 2 batteries are momentarily disconnected. If the battery is OK, stop/start is enabled. Also, there are numerous parameters that have to be met for the stop/start to be enabled. The engine reaching normal operating temp is one of them. If all systems are go, then the ESS will enable when the vehicle reaches operating temps (a few minutes as mentioned above).

• Driver’s seat belt is not buckled.
• Driver’s door is not closed.
• Battery temperature is too warm or cold.
• Battery charge is low.
• The vehicle is on a steep grade.
• Cabin heating or cooling is in process and an acceptable
cabin temperature has not been achieved.
• HVAC is set to full defrost mode at a high blower speed.
• HVAC set to MAX A/C.
284 STARTING AND OPERATING
• Engine has not reached normal operating temperature.
• The transmission is not in a forward gear.
• Hood is open.
• Vehicle is in 4LO transfer case mode.
• Brake pedal is not pressed with sufficient pressure.
Other Factors Which Can Inhibit Autostop Include:
• Accelerator pedal input.
• Engine temp too high.
• 5 mph (8 km/h) threshold not achieved from previous
AUTOSTOP.
• Steering angle beyond threshold.
• ACC is on and speed is set.

 

[Dp7]

Blowing fuses is most likely user error. Jumpstarting the wrong way, not isolating cables during charging/testing or during replacement.

Ignoring symptoms will most likely lead to a no start. A battery charging message on all of the time is sign. Ess unavailable and aux switches stopped working is another sign. The alien warning on the dash is the last warning. You can ignore these and expect have a no start or a shut down.

Yes, user error can blow that fuse too, but that's not what I'm talking about here.

A faulty battery, which gives no obvious indication of a problem (like unusual dash warnings/lights) can inexplicably blow that fuse, leaving the vehicle dead in the middle of the road. Ask me how I know It happened to me while driving home from the dealer who had just "fixed" the N3 fuse blowing a week earlier (they replaced the aux battery, PCR and starter!). I'm not the only one, plenty of threads about it. "ESS unavailable" has so many benign factors like the A/C being on or the engine warming up or a low battery charge or a new moon or a half moon or a blood moon or a solar flare ... it kind of renders that message meaningless - honestly, even the service department said to my wife "that'll go away once you start driving". If one typically manually disables ESS every time they start their vehicle, one tends to ignore the lack of ESS... until they forget to disable it once and the vehicle self destructs the next time you stop.

Almost all of the vehicle electronics are routed through the aux battery wiring. A blown N3 fuse completely isolates that wiring from the main battery and the alternator, causing a "slow death" (if you still have the aux battery installed) as the aux battery runs out of charge. You can drive around, restart your engine several times and everything without knowing N3 is blown. Zero indication.

If you have removed the aux battery ground/F42 fuse, your system electronics are still being fed power through that N3 fuse, which can still pop due to a bad main battery (among other user errors), which will then immediately kill your system electronics since your aux battery has been disconnected and nothing is feeding power to anything at that point.

For anyone who doesn't know, the N3 fuse is not a simple automotive fuse, it's part of a $60 part that you can't get at your local walmart. That's why I suggest bypasssing it with a 150 amp breaker, so it's easily "field reset" if it blows and doesn't leave you stranded. It's also cheaper than a new high amp fuse bar.

 

[JTL21]

How does a bad main battery blow a fuse? Aren’t fuses blown due to excess current draw? How does that happen when a main battery “goes bad”?

 

[Lost1wing]

Under normal circumstances, I don't see a dead shorting a battery taking out a fuse. The current isn't passing through a fuse. Maybe the fuse, off of the alternator circuit could go trying to charge the shorted battery? I think MOST of the fuse array issues are from FAFO occurrences. Yes, even the dealership techs make mistakes. Problem there is that they seldom own their mistakes and sell their misdeeds to the customer. The customer gets some BS story of how it failed, and .ost don't know any better.

Bad connections are a possible reason for hight current flow and fuses going bad. It's something to look at when troubleshooting battery problems.

 

[jebiruph]

ESS will work off of one battery for 6 times in a row. During an ESS event the battery voltages are compared. If the voltages match 6 times in a row, a system fault is assumed and ESS is disabled until the next restart.

 

[Lost1wing]

I do not believe that the above statement is correct. The computer does not "compare" batteries. The computer checks the state of the aux battery when the 2 batteries are momentarily disconnected. If the battery is OK, stop/start is enabled. Also, there are numerous parameters that have to be met for the stop/start to be enabled. The engine reaching normal operating temp is one of them. If all systems are go, then the ESS will enable when the vehicle reaches operating temps (a few minutes as mentioned above).

• Driver’s seat belt is not buckled.
• Driver’s door is not closed.
• Battery temperature is too warm or cold.
• Battery charge is low.
• The vehicle is on a steep grade.
• Cabin heating or cooling is in process and an acceptable
cabin temperature has not been achieved.
• HVAC is set to full defrost mode at a high blower speed.
• HVAC set to MAX A/C.
284 STARTING AND OPERATING
• Engine has not reached normal operating temperature.
• The transmission is not in a forward gear.
• Hood is open.
• Vehicle is in 4LO transfer case mode.
• Brake pedal is not pressed with sufficient pressure.
Other Factors Which Can Inhibit Autostop Include:
• Accelerator pedal input.
• Engine temp too high.
• 5 mph (8 km/h) threshold not achieved from previous
AUTOSTOP.
• Steering angle beyond threshold.
• ACC is on and speed is set.

The f42 fuse controls the power for the power control relay. The computer will momentary open the relay separating the aux and main battery. This it part of the test so that lets ESS know the state of the batteries.

There was never a question here of why it isn't working. It is working and the OP wants to know if it will work on one battery. The answer is yes.

 

[Lost1wing]

I do not believe that the above statement is correct. The computer does not "compare" batteries. The computer checks the state of the aux battery when the 2 batteries are momentarily disconnected. If the battery is OK, stop/start is enabled. Also, there are numerous parameters that have to be met for the stop/start to be enabled. The engine reaching normal operating temp is one of them. If all systems are go, then the ESS will enable when the vehicle reaches operating temps (a few minutes as mentioned above).

• Driver’s seat belt is not buckled.
• Driver’s door is not closed.
• Battery temperature is too warm or cold.
• Battery charge is low.
• The vehicle is on a steep grade.
• Cabin heating or cooling is in process and an acceptable
cabin temperature has not been achieved.
• HVAC is set to full defrost mode at a high blower speed.
• HVAC set to MAX A/C.
284 STARTING AND OPERATING
• Engine has not reached normal operating temperature.
• The transmission is not in a forward gear.
• Hood is open.
• Vehicle is in 4LO transfer case mode.
• Brake pedal is not pressed with sufficient pressure.
Other Factors Which Can Inhibit Autostop Include:
• Accelerator pedal input.
• Engine temp too high.
• 5 mph (8 km/h) threshold not achieved from previous
AUTOSTOP.
• Steering angle beyond threshold.
• ACC is on and speed is set.

This is not my wisdom but from Jeep.

The DBCR ( dual battery control relay) is used by the pcm to control the pcr.

The PCR is placed in between the cranking battery and the aux battery and is used to isolate the two batteries from each other in order to avoid voltage dips when the starter cranks the engine during an ess autostart event. ( main reason to keep the aux battery, unless you use tazer etc. to keep ess off)
The larger battery is responsible for engine cranking. The smaller battery is responsible for managing the vehicles electrical load demand during ess auto stop(engine off).
During ess cranking events, the pcm commands the pcr to open for a calibrated timetable isolate the aux battery.
The DBCR is obd2 diagnosed for short to ground, short to battery and open circuit.
The pcr is also obd2 diagnosed for stuck open and stuck closed. For a stuck closed pcr, obd2 can determine faults based on voltage differences between the aux and main cranking battery. If a stuck closed closed DTC is matured, the pcm busses a signal for the IPC to display an ess message to the driver. For a stuck open pcr, obd2 diagnostics can determine failure on voltage during key on engine on. If a stuck open etc is matured, the pcm also busses a signal for the IPC to display an ess message to the driver.

Both the primary and aux operating parameters are managed by the pcmess logic and are controlled by the dbcr and pcr.

And for those who want to know about the IBS relearn time, it is one start cycle and 4 hours off sleep cycle. This has a major effect on the stop/ start feature.

Again, this is from the service manual.

 

[Andy29847]

ESS will work off of one battery for 6 times in a row. During an ESS event the battery voltages are compared. If the voltages match 6 times in a row, a system fault is assumed and ESS is disabled until the next restart.

I stand corrected. The system does compare batteries. Thanks! You are the #1 resource.

 

[Volt0]

I do not believe that the above statement is correct. The computer does not "compare" batteries. The computer checks the state of the aux battery when the 2 batteries are momentarily disconnected. If the battery is OK, stop/start is enabled. Also, there are numerous parameters that have to be met for the stop/start to be enabled. The engine reaching normal operating temp is one of them. If all systems are go, then the ESS will enable when the vehicle reaches operating temps (a few minutes as mentioned above).

• Driver’s seat belt is not buckled.
• Driver’s door is not closed.
• Battery temperature is too warm or cold.
• Battery charge is low.
• The vehicle is on a steep grade.
• Cabin heating or cooling is in process and an acceptable
cabin temperature has not been achieved.
• HVAC is set to full defrost mode at a high blower speed.
• HVAC set to MAX A/C.
284 STARTING AND OPERATING
• Engine has not reached normal operating temperature.
• The transmission is not in a forward gear.
• Hood is open.
• Vehicle is in 4LO transfer case mode.
• Brake pedal is not pressed with sufficient pressure.
Other Factors Which Can Inhibit Autostop Include:
• Accelerator pedal input.
• Engine temp too high.
• 5 mph (8 km/h) threshold not achieved from previous
AUTOSTOP.
• Steering angle beyond threshold.
• ACC is on and speed is set.

Transmission must be in D, not M.

 

[Blade1668]

Well, I can give some information on what happens in at least one case of the "ESS" battery failure, then leading to vehicle shutdown while moving then wipers to start running really slowly and all lights flashing. Loss of power in steering, brakes, traction control activating randomly.
Leading to 5 codes at least.

And not reading milage right. . I can hope that's what the dealership service department reads it at. My warranty will be in better shape then.
Now on with service department, I have to pay to tow in and they will decide if they will cover it. Kudos to my insurance agent there, of having a local on call one. I limped it on rollback, and we headed to dealership. To late today maybe if luckily tomorrow it will get checked.
A note on service advisor was already trying to figure out how not to honor anything of the Extended Warranty, that was as soon as the salesman that did my sale left. I'm on fairly good terms with him and some others there, they really like my credit score, then a payoff in 4 months.
Not trying to start a pissing match on it yet. Honey or s### gets more flies than salt n vinegar or so I've heard.
But otherwise it's been a really s###y day. I believe I'm going to pour myself a shot or five of bourbon

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