JLUR battery flatlining when flat towing

[mikeq]

Mike, outstanding!!!!!

It all makes sense. When the Jeep is asleep and you reach in with the broomstick handle and press the pedal, there is no current flowing to the lights, and therefore nothing to flow back up the fault-sense wire to the BCM. Conversely, when you apply the brake lights via the RV, the RV supplies power to the light and that circuit board communicates back to the BCM via the fault-sense wire... which triggers the wake-up.

So do you know if the fault-sense wire carries a signal indicating successful illumination or does it send a signal indicating failed illumination?

It seems like it must be a success signal but when I remove those pins, I don't get any errors or messages from the Jeep indicating the tail light is faulty.

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[CoolTech]

So do you know if the fault-sense wire carries a signal indicating successful illumination or does it send a signal indicating failed illumination?

It seems like it must be a success signal but when I remove those pins, I don't get any errors or messages from the Jeep indicating the tail light is faulty.

I'm not sure, Mike. It will be interesting to see if you get any error messages after you have driven it a bit. I suspect and hope you will not. The only thing you are giving up is the ability for the Jeep to alert you when a light is out. Maybe that is a small price to pay to solve the battery drain issue!

 

[mikeq]

I'm not sure, Mike. It will be interesting to see if you get any error messages after you have driven it a bit. I suspect and hope you will not. The only thing you are giving up is the ability for the Jeep to alert you when a light is out. Maybe that is a small price to pay to solve the battery drain issue!

Yeah, I'm just hoping it doesn't constantly tell me I have a tail light out. I suspect though if it does, it's going to be the "health reports" that I get from Uconnect which are easy to ignore. Hopefully it won't be something on the dash.

 

[Jmonroe]

... Another explanation is that the LED-only additional "fault-sense" wire is on the parking light circuits as well. If this is the cause, then keeping the headlights (and therefore parking lights) on, would be a constant-feedback to the BCM waking, and keeping him awake.

This is an interesting theory. Our last trip we drove through a LOT of rain, the lights were on for hours at a time, a couple days in a row without disconnecting the toad/Jeep. This was the case both on our trip north and then again on our return trip back to Florida. In both cases the Jeep was dead upon reaching our destination. Single day trips, albeit long ones, in between, dry weather (no use of lights), no issue.

 

[CoolTech]

Yes, Jay, I think collectively we're on to something. With Mike's testing of both the positive and negative cases - it sure looks like the fault-sense wiring is the culprit. Our recommendation would be to do as Mike did and remove the white plastic retainer on the connector and then push-forward, rotate, and pull that pin either out or down far enough so that it will not make contact. Obviously, this is a completely reversible work-around. Maybe an engineer at Jeep will read this, validate what we have found and maybe there's an opportunity to re-program the Jeep not to wake in this scenario. Until that time, there's a solution - though you will lost the tail light out dash notification. It just means you got to check them every once in a while - just like we used to do!

 

[oceanblue2019]

Yes, Jay, I think collectively we're on to something. With Mike's testing of both the positive and negative cases - it sure looks like the fault-sense wiring is the culprit. Our recommendation would be to do as Mike did and remove the white plastic retainer on the connector and then push-forward, rotate, and pull that pin either out or down far enough so that it will not make contact. Obviously, this is a completely reversible work-around. Maybe an engineer at Jeep will read this, validate what we have found and maybe there's an opportunity to re-program the Jeep not to wake in this scenario. Until that time, there's a solution - though you will lost the tail light out dash notification. It just means you got to check them every once in a while - just like we used to do!

I just did a test and with the fault-sense wire disconnected the light out indicator comes on within minutes of driving the Jeep.

So while disconnecting solves the battery drain issue when being towed, it is a nuisance when Jeep under its own power.

I bet a relay could be wired to disconnect the fault sense when 12V power is provided by the RV, but when not present they are closed to allow the Jeep to function as intended. A little more complexity and wires to be run....

 

[mikeq]

I just did a test and with the fault-sense wire disconnected the light out indicator comes on within minutes of driving the Jeep.

So while disconnecting solves the battery drain issue when being towed, it is a nuisance when Jeep under its own power.

I bet a relay could be wired to disconnect the fault sense when 12V power is provided by the RV, but when not present they are closed to allow the Jeep to function as intended. A little more complexity and wires to be run....

Strange, I have not had the light out indicator come on. I've only driven a short 5 minute trip since disconnecting the fault sense pin though.

 

[CoolTech]

Strange, I have not had the light out indicator come on. I've only driven a short 5 minute trip since disconnecting the fault sense pin though.

Mike, did you disconnect the fault sense pins for all 4 lights (right parking, right turn, left parking, left turn)?

 

[oceanblue2019]

Strange, I have not had the light out indicator come on. I've only driven a short 5 minute trip since disconnecting the fault sense pin though.

Hmmmm. A few questions:

- Do you have any aftermarket replacement lights? I have heard some of these cheat the fault signal by tying it to ground.

- Do you have a TAZR? It has a setting to change the behavior of the LED out sense - perhaps that is set on?

 

[mikeq]

Mike, did you disconnect the fault sense pins for all 4 lights (right parking, right turn, left parking, left turn)?

No, just the brakes. Next time I'm hooked to the RV I'll look at the signals and parking light behavior to see if that's needed.

I don't think for the rears anything needs to be done though. Looking at the wiring diagram you posted, there's only a single fault-sense for the each rear light which I suspect covers park, signal and stop. This is the gray/white wire that I already pulled the pin on.,

Come to think of it, when I installed the mopar tow harness, there's nothing connected to the front lighting so the front lights may not be an issue. I know that the front turn signals don't come on when the RV is hooked up. I suspect the park lights on the front don't either.

 

[mikeq]

Hmmmm. A few questions:

- Do you have any aftermarket replacement lights? I have heard some of these cheat the fault signal by tying it to ground.

- Do you have a TAZR? It has a setting to change the behavior of the LED out sense - perhaps that is set on?

I have aftermarket front LED turn signals and markers but those aren't wired into the tow harness.

I do have a TAZR but the setting for the lights are default for a Rubicon. The rear brake lights are factory LED. The only thing I have reprogrammed with the TAZR is the being able to use the backup camera while driving and enabling the AUX switches that I added. Aside from that everything is stock.

 

[CoolTech]

Mike, of course you are right. I'm wondering if the difference is that maybe you tested briefly without the parking lights on and perhaps John (oceanblue2019) tested in the evening with parking lights/headlights on. That may explain why he got a bulb out message and you didn't?

 

[mikeq]

Mike, of course you are right. I'm wondering if the difference is that maybe you tested briefly without the parking lights on and perhaps John (oceanblue2019) tested in the evening with parking lights/headlights on. That may explain why he got a bulb out message and you didn't?

Ah, sorry. My misunderstanding. I'll take the Jeep out for a spin later with the park/headlights on.

 

[mikeq]

Ah, sorry. My misunderstanding. I'll take the Jeep out for a spin later with the park/headlights on.

Tested with park/headlights. Still no light out warning.

 

[Dsdbkranz]

Hello new here and just read this entire post. Very informative. I towed my 2020 Jeep Wrangler Rubicon 4 door for the first time. It was a 13 hour drive and when I got to my destination the jeep was dead. I have LED lights and I installed the road master diode kit. I’m getting ready to go again and was thinking about cutting the gray wires (feedback sensors) and putting a temp toggle switch for both rear lights until I get home. Based on the conversations that’s the problem with the LED light setup. I’ll let you know how that works out.

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