Jumperless Aux Battery Bypass

[Swagger]

Absolutely (at least it did in my case and threw codes + check engine light).

Did you also disconnect the auxiliary negative battery cable from the main battery and insulate it?
Did you clear the codes?

I pulled the fuse, disconnected the aux battery and wrapped the cable but did not clear the codes. I was time constrained and thought that the bypass would be enough, but maybe the codes put it in limp mode permenantly. Its been 3 years since the batteries have been replaced, so I wlll probably do that and see if it works. If not, the off to dealership for me. AGMs would be the best, right?

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[CarbonSteel]

I pulled the fuse, disconnected the aux battery and wrapped the cable but did not clear the codes. I was time constrained and thought that the bypass would be enough, but maybe the codes put it in limp mode permenantly. Its been 3 years since the batteries have been replaced, so I wlll probably do that and see if it works. If not, the off to dealership for me. AGMs would be the best, right?

I would clear the codes. What I found is I had a left bank running lean code and a number of others. All cleared except the lean code because it is permanent and the condition that caused the code has to clear before it will automatically clear. Once I sorted the battery issue, it cleared, but the engine started running better almost immediately after I cleared the other codes.

I would clear them first and see how it runs and after putting a few miles on it check and see if there are any other codes. I am still leaning towards the battery being the root cause and if you replace it, you have to use AGM--the system is designed around them and not lead/acid batteries.

 

[Heimkehr]

Would bad batteries cause the engine to misfire?

Is there a easy way to determine which problem it might be?

Possibly. The only direct experience I have with a misfire occurred when a coil pack on a brand new VW failed. It was replaced under warranty, which restored proper running.

A battery reaching the end of its practical service life can be the cause of a variety of seemingly unrelated issues, like a series of dashboard warning lights illuminating concurrently. Further, resting voltage can appear OK (e.g., 12.4V) and then drop off a cliff when attempting to crank the engine. A load test should provide additional intel here.

If the batter(ies) in your '18 are original to the vehicle, do consider replacing one (or both, if present) as a prophylactic measure. Use a quality AGM from a well-regarded brand.

As for the CEL, what code(s) are being displayed? You can pull them using an OBD-II code reader, and, I believe, JScan.

 

[Swagger]

As for the CEL, what code(s) are being displayed? You can pull them using an OBD-II code reader, and, I believe, JScan.

jl p0300, p0301, p0133, p0171 were the codes I was getting.

 

[Heimkehr]

jl p0300, p0301, p0133, p0171 were the codes I was getting.

300 is misfires "on several cylinders".
301 is a misfire in cylinder 1.
133 is a problem with the O2 sensor (Bank 1, Sensor 1).
171 is "the oxygen (O2) sensor on bank 1 sent a signal to the engine control module that the air-fuel mixture is too lean to be corrected."

They're all interrelated enough, in my view, to suspect a genuine mechanical issue in lieu of a wonky battery. I might consider starting with O2 sensor replacement, if it's low-hanging fruit in terms of easy replacement.

 

[CarbonSteel]

300 is misfires "on several cylinders".
301 is a misfire in cylinder 1.
133 is a problem with the O2 sensor (Bank 1, Sensor 1).
171 is "the oxygen (O2) sensor on bank 1 sent a signal to the engine control module that the air-fuel mixture is too lean to be corrected."

They're all interrelated enough, in my view, to suspect a genuine mechanical issue in lieu of a wonky battery.

I should have recorded the ones that I had, but they were very similar if not exactly the same--particularly 171.

171 was exactly the same and it is a "permanent code" that will not clear until the root cause is resolved.

My codes were 100% related to the bad auxiliary battery.

 

[Sting Gray Rubi]

You pulled F42 and you disconnected the Aux Neg cable ..... if you are randomly seeing the Aux switches not available EVIC notice, and remote start fails ....it's because your Main battery is iffy.

Replace the Main with an H7 as soon as possible.

https://www.jlwranglerforums.com/forum/threads/??-main-battery-replacement-talk-jl-jt-?.100534/

I'm reading that many are going to the 94r battery when the aux is eliminated....the 94r and H7 both have 850 cca.

 

[Swagger]

I should have recorded the ones that I had, but they were very similar if not exactly the same--particularly 171.

171 was exactly the same and it is a "permanent code" that will not clear until the root cause is resolved.

My codes were 100% related to the bad auxiliary battery.

Thx, thats the problem, people are seeing the same symptoms and codes with a valve cover oil leak onto the o2 sensor. Problem could be one or the other or both. Since I suspect a bad aux battery, and the batteries are 3 years and 50k miles old, I am going to replace the batteries first and see if that works, because the valve cover leak will be a dealer visit with 2 week delay before they can even look at it.
I will report back what happens as I work through this. Thanks everyone for all your insight and help.

 

[Greendezl]

Don’t screw around with factory crap. I deleted my Aux and added an Odyssey. Granted it’s easy to do on the diesel but still fairly easy on the others. Here is a great price with free shipping.

https://www.fcpeuro.com/products/automotive-battery-group-94r-odyssey-94r-850

 

[CarbonSteel]

Thx, thats the problem, people are seeing the same symptoms and codes with a valve cover oil leak onto the o2 sensor. Problem could be one or the other or both. Since I suspect a bad aux battery, and the batteries are 3 years and 50k miles old, I am going to replace the batteries first and see if that works, because the valve cover leak will be a dealer visit with 2 week delay before they can even look at it.
I will report back what happens as I work through this. Thanks everyone for all your insight and help.

It may not be your battery (though it could be). My threw codes again today and the ESS @! light came on, but the engine light did not. When I checked the codes it was post-catalytic lean condition. I had an oil leak on the passenger side of the engine and I am now suspecting that I have a failed/failing 02 sensor.

Two times that it has happened recently is when I have gone above 9K feet elevation. I can clear the codes and it begins to run normally after that. Time to investigate replacing the 02 sensor. My aux is fully disconnected, ESS turned off by Smart Start/Stop, and the F42 fuse pulled. I cannot think it is the actual ESS system that is at fault (this time) by is merely a symptom of the other issue.

 

[Swagger]

It may not be your battery (though it could be). My threw codes again today and the ESS @! light came on, but the engine light did not. When I checked the codes it was post-catalytic lean condition. I had an oil leak on the passenger side of the engine and I am now suspecting that I have a failed/failing 02 sensor.

Two times that it has happened recently is when I have gone above 9K feet elevation. I can clear the codes and it begins to run normally after that. Time to investigate replacing the 02 sensor. My aux is fully disconnected, ESS turned off by Smart Start/Stop, and the F42 fuse pulled. I cannot think it is the actual ESS system that is at fault (this time) by is merely a symptom of the other issue.

Did you get the oil leak fixed? Was it coming from the valve cover gasket?
Strange that you threw codes but the cel didn't come on. Are you still misfiring?

 

[CarbonSteel]

Did you get the oil leak fixed? Was it coming from the valve cover gasket?
Strange that you threw codes but the cel didn't come on. Are you still misfiring?

Yep, it was the hose on the PCV. The CEL came on the last time, but not this time. Only the @! light for ESS.

It can't be ESS though...no aux, no fuse, and Smart Start/Stop.

It seems to only happen when I go up in elevation (for now).

I picked up a new 02 sensor a bit ago. Now to see how much of a PITA it will be to change it.

 

[CarbonSteel]

So the plot thickens...

Changed my high amp fuse array today and N3 was not blown--though strangely enough and despite having the towing package +auxiliary switches, I had the 60amp version.

I have a Gladiator fan (850 watt) to install so I'm glad I grabbed the 100 amp version.

With that said, I believe I have a false positive for ESS and battery issues and instead think I have an O2 sensor issue given the codes that are being thrown and service ESS is just a consequence.

Was going to change the O2 sensor until I saw where it was, so I guess I'll get to flex that MaxCare warranty in the near future.

N3:

 

[Swagger]

Thanks for the info! While changing the batteries, I'll be on the lookout for potential oil leaks around the O2 sensors. Hopefully not the case, because thinking dealer service if thats the case, but we'll see I guess.

 

[Swagger]

Update: after removing the fender to replace the aux battery, I found an oil leak. Happened to be above the o2 sensor attached to the exhaust manifold closest to the engine on passenger side. Sensor looks a little toasted from the burnt oil residue on it, so thats probably why I'm having this problem. Thought it was the valve cover gasket - there was oil there, but found the oil was coming from obove there.
About a year ago, i put a catch can in that attaches to a tube coming off the valve cover (I think, please correct me if I'm wrong). This tube is right above the sensor and the hose attached from the catch can was very wet from oil there, and i think is where the oil is coming from that is dripping on the sensor. So good news is valve cover gasket is ok, but sensor probably not.
Luckily, I still have the original oem tube that connects there, so removed the catch can, replaced the hose with oem, and see what happens.
Anyone know how difficult it is to replace that sensor? I still have the fender off so I can see it pretty good.

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