2018 Jeep JK - trouble (re)starting when hot

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BikeManDan

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My friend has a 2018 Jeep JK with about 50,000 miles. Occasionally she has trouble (re)starting it when the engine is hot. The typical scenario is she drives is an hour or so, then stops to get gas, and it won't start when she wants to leave. She's had to two Jeep dealers, but both found nothing. Any ideas would be appreciated.
 

El-Dracho

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Such remote diagnoses are of course always super difficult. A very precise description of the problem is helpful. So it's best to start at the beginning. I assume 3.6 V6 gasoline engine? What modifications has been done to the rig, especially wrt to the engine? What exactly has already been tested, when and with what result?

I am not the jeep expert, but the more and more detailed information you provide, the easier it will be for someone here who knows the vehicle to help you.
 

BikeManDan

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Sorry, of course I should have been more thorough in my description. I also understand that a diagnosis my not be possible, but suggestions are appreciated. Yes, the JK has the 3.6 V6 with no engine modifications. The only thing the 2 dealers have done is to run diagnostic scans and no codes came up.
 
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El-Dracho

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Just out of the blue: Maybe a sensor delivers wrong values when it is warm? Maybe too low fuel pressure when warm? It should be possible to find such things systematically with a diagnostic tester (e.g. evaluate live data). Did the dealers do this or just read out error codes?

Maybe a control unit has a defect when it gets warm? From my experience, however, this is more of an issue when the control units get old. There you can have "funny" things that you search for long time. Sometimes it helps to cool the suspected component and see if the error then also occurs.

But let´s wait for the Jeep experts here if they come up with something which is typical for this rig.
 

socal66

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There has been a known issue with 2018 JK’s and either the temperature sensor in the transmission was faulty or the valve body in the transmission needs replacement as vehicles needed to have the transmission cool down over 5-30 minutes before restarting again. I think there is a Jeep service bulletin on this and they should have the dealer look in this direction as a possibility.
 

DRAX

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You haven't said what "no start" actually means, either. Engine turns over but won't start? That would be fuel or ignition. Engine won't even turn over? That would likely be an issue with the security/keyless ignition system. That said...


The common problem seems to be related to the aux (ESS) battery used for the electronics.


Surprised the dealers don't know about this common problem. May want to see about doing the ESS battery bypass and see if the problem goes away.
 
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