Two problems related to transmission sensor have been reported for the 2008 Jeep Wrangler. The most recently reported issues are listed below.
When the ignition key was turned to on, the starter only gave a click. After sveral attempts it started. The dealer did a diagnostic and found nothing. The problem continued and became more frequent and severe to the point it wouldn't start after numerous attempts. The starter was replaced with no results, problem continued. From online forums on Jeep I found this to be a widespread problem. It was suggested to put the automatic transmission in the neutral position and try. If it starts, the problem is a faulty transmission range sensor. Putting it neutral when this occurrs, has started the engine the first try dozens of times for me. I took the Jeep to the dealer, gave them this information which they ignored. They replaced a solonoid cable instead. The problem contiued. Returned to the dealer for another diagnostic, they kept the vehicle for 2 days while I rented a vehicle. Nothing was found or fixed in their diagnostic when I picked it up. The problem continues, it did it today twice 6/25/2014, but still starts in neutral for now. The suggested transmission range sensor would be covered in my lifetime powertrain warranty. I believe Jeep knows there is a problem but chooses to ignore it. This seems to effect wrngler models from 2007- 2012 years. It is so widespread it should be a recall issue. Starting in neutral is not a fix.
There is a widely experienced (though unacknowledged by Chrysler) issue concerning failure to start on automatic transmissions jk. While in park, turning the key will produce a single click but not crank. If you push the shift lever, while in park, up a little more, or, move the shift lever into neutral, the vehicle starts. The cause of the issue is a poorly designed, easily fatigued transmission range sensor (trs), and/or a weak ground of the same.