Jeep Won’t Start After Flat Tow

[fairway2002]

If you have a remote start try that. It goes around security. Will help determine problem.

[Dreamer Easy]

Originally Posted by YC1

Stunned by this but sounds like a fun one to chase down.

I would get a voltmeter onto the posts where the aux battery connects. They showed that removing that battery from the system makes it look like things should work but apparently do not.

However, the aux battery alone is enough to start the thing and also supplies enough power to the fuse block that everything works, including the charging with the alternator.

If the aux battery is sick or just gets run down while towing it is easy to see why it won't start based on this video. Your charge line may NOT be charging the aux battery.

I tried to zoom in on the schematic in the video but still can't get a clear picture.

Any chance that battery is some sort of Lithium?? Just curious.

With the keyless start systems there can be a huge draw while towing and a small battery could be run down easily.

I would love to see the Aux battery checked and even before doing that I would connect the charge line wiring to the toad and measure the voltage on the posts where they took the battery cable off on the fuse panel. This would be to verify the aux battery is getting charged enough.

If you can come up with a schematic for the jeep system and post it there are lots of folks here that can sort it out.

I will check to see if the line is charging the AUX.
Don't know about a Lithium AUX - kind of doubt it.
Couldn't find a Starter/Charging schematic but here's a video version!

https://www.youtube.com/watch?v=rvwqZa9vhRc

[Dreamer Easy]

Originally Posted by jtyphoid

Besides the batteries, I would look at whether the vehicle has any safety lockouts for the starter, like a shift position sensor that would prevent starting if the transmission selector is is in drive.

Thanks, jtyphoid. I believe that the safety lockouts the driver has control over are shift position, door closed, and foot on the brake. The others are handled by sensors.

[Dreamer Easy]

Originally Posted by HenryRH3

I have had the same problem intermittently. Don’t ask me how or why, but if I push the brake pedal really hard, it will start every time.

Thanks HenryRH3. Mine is intermitted too. I'm not sure what to make of the brake pressure. Why not try it!

[Dreamer Easy]

Originally Posted by fairway2002

If you have a remote start try that. It goes around security. Will help determine problem.

Thanks fairway2002. I had not thought of that. I'll give the remote start a try.

[YC1]

Originally Posted by Dreamer Easy

Thanks fairway2002. I had not thought of that. I'll give the remote start a try.

I believe this could be the solution too. There are parallel paths to start the vehicle based on the video. One is the dash switch of course and the other is the key fob.

The person pushing the brake pedal may be causing the computer system to reset some lockout function. It may not be because of pressing it hard rather than the slightly longer time of pushing it.

This dual battery system is a recipe for many crazy issues and I can't say I am a fan of the design.

With so many computers onboard and having a battery go low and still be at the threshold of starting a vehicle the load of the starter would drop the voltage even lower and we know what a brown out can do to a computer. Blues screen, lock ups etc.

Looking at the video I suspect there are all kinds of lockouts and it seems the charge line of the alternator may be interrupted for a few moments until the engine reaches a certain rpm for example.

I would still check to see that the Aux start battery is not getting run down. A jump start cable between the engine battery and the Aux start battery would eliminate the question but if you can get a voltage measurement immediately after stopping while towing and have not yet disconnected the charge line while leaving the RV running it could be a useful measurement.

I bet the poor techs that worked on it could not duplicate the problem and after disconnecting the batteries the problem resolved. The old Intermittent trouble.

Keep us posted. This is a very interesting thread.

[Dreamer Easy]

Originally Posted by YC1

I believe this could be the solution too. There are parallel paths to start the vehicle based on the video. One is the dash switch of course and the other is the key fob.

The person pushing the brake pedal may be causing the computer system to reset some lockout function. It may not be because of pressing it hard rather than the slightly longer time of pushing it.

This dual battery system is a recipe for many crazy issues and I can't say I am a fan of the design.

With so many computers onboard and having a battery go low and still be at the threshold of starting a vehicle the load of the starter would drop the voltage even lower and we know what a brown out can do to a computer. Blues screen, lock ups etc.

Looking at the video I suspect there are all kinds of lockouts and it seems the charge line of the alternator may be interrupted for a few moments until the engine reaches a certain rpm for example.

I would still check to see that the Aux start battery is not getting run down. A jump start cable between the engine battery and the Aux start battery would eliminate the question but if you can get a voltage measurement immediately after stopping while towing and have not yet disconnected the charge line while leaving the RV running it could be a useful measurement.

I bet the poor techs that worked on it could not duplicate the problem and after disconnecting the batteries the problem resolved. The old Intermittent trouble.

Keep us posted. This is a very interesting thread.

I think it’s solved now after taking the Jeep and RV back to the dealer who installed the tow package.

As you may recall (or not) the problem was either rooted in the electrical system (battery and all the sensors that have to read “go” for the starter to engage) OR possibly mechanical (brake pedal pressure or some other such evil).

So, which was it?

It was the Jeep’s battery(s) being drawn down while being towed.

How was it corrected? By adding a Pollak circuit breaker.

What does the Pollak circuit break do? It prevents the battery from being drained from auxiliary applications.

Here is a 2-minute video that explains the part at the bottom of this link:

https://www.etrailer.com/Accessories...k/PK54540.html

If this doesn’t work, I’ll be back for more of your help.

[Lt Dan]

You might try pulling the brake light fuse before you tow or install a brake light cutoff switch in the brake wiring. There is a possibility it's getting a backfeed from the wiring harness into the computer with the Jeep activating the brakes at the same time the wiring harness is getting a signal from the coach.

[YC1]

I couldn't find the video. Did they install something that allows you to shut off power? A breaker can have that option.

Your charge line should be able to keep up but these keyless vehicles are hungry animals and need a really good line. I use a heavy duty connector and can supply 40 amps.

Thanks for keeping us posted.

[NXR]

It was the Jeep’s battery(s) being drawn down while being towed.

How was it corrected? By adding a Pollak circuit breaker.

What does the Pollak circuit break do? It prevents the battery from being drained from auxiliary applications.

It's not going to help unless what they actually did was to install a battery charge line from the motorhome to the Jeep and used that breaker to protect the charging circuit.

That breaker will allow up to 40 amps to flow and then it will trip for a sort while, automatically restoring the power. once it cools down A 40 amp drain will kill a battery fairly quickly even if it's interrupted occasionally.

Since the dealer installed some kind of "tow package" you may not have had a charge line previously. Do you know whether you did?

Ray

[WhippetTaxi]

This is really a long shot, but...I recently discovered an issue with my Jeep not starting that was because I had not closed the driver’s door before pushing down the brake pedal and the start button.

[CoolTech]

OP -

The problem is the people you are letting work on your Jeep and which are charging you for things you don't need to cover their mistakes.

As you say, the "power" for your Air Force One is compressed air coming from the MH. There is no power that is required from the Jeep. Further, the power that operates your brake lights and turn signals is also coming from the MH - via the trailer connector.

Finally, the correct way to tow the Jeep (as your are doing) is with the ignition in the OFF position.

Do we agree on all of the above?

Assuming we do, then the real question is why the heck do you have a charge wire going from the MH to the Jeep?? There should be no need for that and I think in doing that they have muffed something up and/or possibly not allowing the Jeep to go into SLEEP mode.

In looking at the Air Force One instructions, the DO use local Jeep power for the very small LED "indicator light" that is most often mounted on the back side of the Jeep's mirror. That LED power draw should only occur when the Jeep's brake pedal is depressed and the power draw should be close to nil - certainly not enough to warrant a concern about the Jeep's battery.

Sleep mode: 1-2 minutes after the last door is closed, the Jeep will go into a very-low-current-draw sleep mode. This is what lets the Jeep sit in your garage for 3-4 weeks and then fire right up when you need it. Easy enough to test the sleep mode. Roll down the driver's window and exit the Jeep with key in hand. Wait 2-3 minutes. Now, stick the handle of a broomstick in through the open window and depress the brake pedal. The rear brake lights will NOT illuminate - the Jeep is in Sleep mode.

I really doubt the circuit breaker has anything to do with your problem - but maybe they fixed something along the way. If you go back to them, I'd have them remove the charge wire to the Jeep as it just doesn't make any sense.

[YC1]

I doubt it goes into a deep sleep mode when placed into the towing position. My Ford Edge Limited had the keyless ignition and was a power pig even when it went into the sleep mode but in the towing position.

It would be easy to measure the current draws of course and if one of the batteries is actually bad it would take a talented and dedicated tech to sort it out.

I watched a battery in a BMW that would start the car just fine but if any load at all, and I mean even <1 amp drew on the battery that in almost exactly 20 minutes the thing would drop to 8.5 volts.

That thing was miserable to sort out but batteries can do really strange things. I found one that went dead and a simple jump should have got things going. The alternator was putting out just fine. However, the second the person put it in gear to drive off and it would die. After replicating the problem several times we dropped in an old spare battery laying around and it worked just fine. The only thing I can surmise is that the original battery just did not filter out the Large DC spikes from the alternator and those spikes confused the electrical systems of the vehicle.

This is a quick summation of course but the point is a battery can be the problem even though it seems to do what it is supposed to do.

As for that breaker. IF that is all they installed it would be important to see where and how they installed it.

A diode isolator to keep both batteries up to speed might be inline but sure seems like doing whatever was done may work but could be masking the real problem.

[CoolTech]

Originally Posted by YC1

I doubt it goes into a deep sleep mode when placed into the towing position. My Ford Edge Limited had the keyless ignition and was a power pig even when it went into the sleep mode but in the towing position.

I absolutely guarantee you that the Jeep Wrangler SHOULD be in sleep mode when being towed. In fact, there is literally no "towing position" that the Jeep is testing for or cares about. The only towing position is the fact that the transfer case is in neutral. There is NO sensor for this and the Jeep doesn't "know". But, it is also easy to test with my broomstick through the window routine.

We've been making towing harnesses for the JL since before it's public release and I'd venture to guess we have one of the most popular kits available and hundreds of users.

The Wrangler JL's WILL sleep. If AIR is used for the aux brake controller, there is nothing* that will draw down the Jeep's battery. (*) The small indicator LED in the AFO kit is harmless in its current draw.