JLUR battery flatlining when flat towing

[CoolTech]

OK, So if I don't have it and I still have the issue, would that potentially indicate that the BLIS system is not the culprit?

It's a good datapoint.... but there could be more than one cause!

Can you address my question of how your brake indicator LED is wired?

Sponsored

 

[JimN]

I'll look into it tomorrow.

 

[Jmonroe]

In earlier posts I'd indicated that our batteries had gone dead in spite of having an RVI toad charger installed. Today I decided to double check the installation and found the "ignition hot" position on the Jeep side of the wire harness was wired incorrectly. I've now corrected that and I expect, fingers crossed, that will prevent DOA batteries going forward.

It'll be October before we travel far enough to confirm in practice but I'm pretty confident I've got a handle on this, finally.

 

[TJDave]

Can we get a very quick poll going to see if we can hone in on the problem? If you currently are towing a Wrangler or Gladiator, can you please provide the following information?

1. What type of Light Wiring Harness do you have?
2. What type of Aux Brake Controller do you have?
3. Does your Jeep have the LED Light option?
4. Does your Jeep have BLIS option?
5. Do you have the battery drain issue?

If we can get the answers to these questions from a few of you, it would be VERY helpful in trying to get to the bottom of this problem. THANKS!

1. Cooltech
2. RVi3 brake powered by RVi3 battery direct 12v outlet.
3. LED yes
4. BLIS yes
5. No battery drain issues. But, our longest trip has only been 4 hours. 6 hour trip coming up. Reading this thread scares me!

 

[gm920]

All... please trust that we understand how frustrating this problem may be and we are sincerely VERY interested to help diagnose and solve the problem.

Typically when towing a Jeep an owner will install a wiring kit and some type of aux brake controller. Early-on in this thread I speculated that the cause of the "battery drain" was likely due to the fact that the Wrangler was not staying in its 'sleep-mode". The more info that is documented in this thread tends to reinforce that we were correct in this speculation. So, instead of trying to find some random current draw somewhere, what we need to find is what is causing the Jeep to wake up and not go back to sleep. (The not going back to sleep is still a little confusing for me. I would think that some day soon we will find what is waking up the Jeep but it is still a bit of a conundrum as to why it will not go back to sleep.)

OK, so I think we are largely correct that the Jeep is coming out of - and presumably staying out of sleep-state.

I have a couple of theories as to why that is happening:

1. Undesired feedback through the "fault sense" wire going to the LED lights, and/or;
2. Undesired feedback through the "blind spot indicator" BLIS system.

Can we get a very quick poll going to see if we can hone in on the problem? If you currently are towing a Wrangler or Gladiator, can you please provide the following information?

1. What type of Light Wiring Harness do you have?
2. What type of Aux Brake Controller do you have?
3. Does your Jeep have the LED Light option?
4. Does your Jeep have BLIS option?
5. Do you have the battery drain issue?

If we can get the answers to these questions from a few of you, it would be VERY helpful in trying to get to the bottom of this problem. THANKS!

1. What type of Light Wiring Harness do you have?
DIY cooltech clone, with automatic switching via relay
2. What type of Aux Brake Controller do you have?
Ready Brake, cable operated surge brake system
3. Does your Jeep have the LED Light option?
Yes
4. Does your Jeep have BLIS option?
Yes
5. Do you have the battery drain issue?
No

2019 JLUR 3.6L

 

[Jgam]

I have LED's . I have the Roadmaster universal diode kit. I do not have BLIS. I do not have auxillary brakes. I do have the battery drain issue.
It takes more than one full day to drain down the battery.

 

[mikeq]

I'm experience battery drain when towing as well. I've found that if I have the Jeep disconnected from the RV (no trailer harness connected), the Jeep behaves as expected. The vehicle goes to sleep and pressing the brake pedal does not wake the jeep up. When the tow harness is connected, the Jeep wakes up when the pedal is pressed. Both times a wait period of ~5 minutes was used.

I'm wondering if the LED option is causing CAN bus traffic that wakes the Jeep up. It would be interesting to know if anyone with the non-LED option has this issue.


1. What type of Light Wiring Harness do you have?
Mopar Tow Harness

2. What type of Aux Brake Controller do you have?
Airforce One

3. Does your Jeep have the LED Light option?
Yes

4. Does your Jeep have BLIS option?
Yes

5. Do you have the battery drain issue?
Yes

2021 JLUR 3.6l

 

[CoolTech]

mikeq - thanks a lot for your thoughts and input.

It is interesting for me that even some cases with the Mopar Harness are also experiencing this. My tendency is to think that it may NOT be the harness - but the aux brake controller. In your case, with the AF1, do you know specifically how the brake monitor light of that kit was wired?? I think it would be prudent to try to eliminate this as a potential cause. Thanks for any additional info.

 

[mikeq]

mikeq - thanks a lot for your thoughts and input.

It is interesting for me that even some cases with the Mopar Harness are also experiencing this. My tendency is to think that it may NOT be the harness - but the aux brake controller. In your case, with the AF1, do you know specifically how the brake monitor light of that kit was wired?? I think it would be prudent to try to eliminate this as a potential cause. Thanks for any additional info.

The LED brake indicator draws power from the car battery. It's nothing more than a switch that is attached to actuator on the brake pedal. When the actuator moves, the switch is activated and turns on the LED. It has no connection to any other system.

 

[CoolTech]

mikeq- thanks!

I realize that this is exactly the way the (reed) switch is SUPPOSED to be wired but the reason I asked is that some installers may try to take a short-cut and wire the hot leg instead to a wire already internal to the Jeep. But, you can confirm that in your case, they took this wire, somehow passed it through the firewall and then connected it to the Jeep's battery?

Please don't mistake to basis of my question. There's no way the smallish LED would draw down the Jeep battery, but if the hot-leg of that was NOT wired directly to the battery, it could be a candidate as something that is causing the Jeep to wake-up.

 

[mikeq]

mikeq- thanks!

I realize that this is exactly the way the (reed) switch is SUPPOSED to be wired but the reason I asked is that some installers may try to take a short-cut and wire the hot leg instead to a wire already internal to the Jeep. But, you can confirm that in your case, they took this wire, somehow passed it through the firewall and then connected it to the Jeep's battery?

Please don't mistake to basis of my question. There's no way the smallish LED would draw down the Jeep battery, but if the hot-leg of that was NOT wired directly to the battery, it could be a candidate as something that is causing the Jeep to wake-up.

I was the installer and yes it was run through the firewall to the battery.

FYI, I'm a retired electrical/software engineer so I enjoy diagnosing things like this.

I'm going to try an experiment today. I'm going to remove the tail lights and unplug them. Then, I'll hook up the Jeep to the RV and perform the "sleep test". If the Jeep doesn't wake up with the tail lights disconnected, then I suspect that it's a CAN bus issue.

The LED lights have a controller in them and I'm thinking that when power is applied to the LED tail light, the controller sends information on the CAN bus to the Jeeps main ECU causing it to wake up.

 

[CoolTech]

The LED lights have a controller in them and I'm thinking that when power is applied to the LED tail light, the controller sends information on the CAN bus to the Jeeps main ECU causing it to wake up.

Mike - awesome! Fully agree. A suspect for us is that on LED-equipped Wrangler's, the fault-sense wire (see OEM diagrams attached) is carrying a voltage back to the BCM. If there was a way for you to isolate the fault-sense wire, that would be great.

The other head-scratcher here is that we know that something is causing the Jeep to wake up. What is still a mystery for me is why it seems to STAY awake. It would seem that one day we may find what is triggering the wake-up but then we also need to determine why it doesn't go back to sleep..... or maybe it does, just to be woken up again. 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.

 

[mikeq]

Mike - awesome! Fully agree. A suspect for us is that on LED-equipped Wrangler's, the fault-sense wire (see OEM diagrams attached) is carrying a voltage back to the BCM. If there was a way for you to isolate the fault-sense wire, that would be great.

The other head-scratcher here is that we know that something is causing the Jeep to wake up. What is still a mystery for me is why it seems to STAY awake. It would seem that one day we may find what is triggering the wake-up but then we also need to determine why it doesn't go back to sleep..... or maybe it does, just to be woken up again. 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.

Confirmed. It's the communication back to the BCM through the fault-sense wire.

I removed both taillights and applied brakes on the RV. Jeep did not wake up.

Removed the fault-sense pin from the harness, reattached the lights and applied the brakes. Jeep did not wake up. Taillights and turn signals worked when actuated.

Re-installed the fault-sense pin, put the brakes on the in the RV, Jeep woke up.

Interestingly enough, when the brake pedal is pushed through the window with a broom handle, the pedal doesn't trigger the brake lights. It seems like the Jeep is smart enough to ignore the pedal press when it's asleep but not smart enough to ignore the fault.

I'm assuming this is because the circuit board in the LED taillight is alive from the 12v supplied by the RV and it initiates the signal.


I don't know what the legality or other impacts might be for doing this. This was just for diagnostic purposes.

On the LED taillight assembly:

remove the white cover
push the pin show forward out of the connector for the gray wire
rotate the pin 180 degrees
pull it back down into the connector to where it sits far below the other pins.

 

[mikeq]

The other head-scratcher here is that we know that something is causing the Jeep to wake up. What is still a mystery for me is why it seems to STAY awake.

I don't think it's staying awake. It's just that it is constantly being woken. Turn signals also cause it to wake up. It takes my Rubicon 5 minutes to go into full sleep (measure with an amp draw on the battery). It actually goes through a couple stages of shutdown before fulling going to sleep. Over a 5 minute period, I'm likely to use brakes, turn signals or diesel brake and wake up the Jeep again.

The first time our battery died, we hit an hour long bumper to bumper traffic jam going through the George Wallace Tunnels. Later the same day, we hit another similar traffic jam in Texas. It was a long day with a lot of stop and go. I have no doubt the Rubicon was awake for most of that trip.

 

[CoolTech]

Confirmed. It's the communication back to the BCM through the fault-sense wire.

I removed both taillights and applied brakes on the RV. Jeep did not wake up.

Removed the fault-sense pin from the harness, reattached the lights and applied the brakes. Jeep did not wake up. Taillights and turn signals worked when actuated.

Re-installed the fault-sense pin, put the brakes on the in the RV, Jeep woke up.

Interestingly enough, when the brake pedal is pushed through the window with a broom handle, the pedal doesn't trigger the brake lights. It seems like the Jeep is smart enough to ignore the pedal press when it's asleep but not smart enough to ignore the fault.

I'm assuming this is because the circuit board in the LED taillight is alive from the 12v supplied by the RV and it initiates the signal.

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.

Sponsored