[Lou C]

It could be clogged or a loose spin on filter in the trans pan. I just had this happen on my '07 WK 5.7 with the Chrysler 545RFE 5 speed trans. It was working just fine not one problem all these years and then one day it refused to go into gear. Luckily for me it happened in the driveway at home! It also popped a P0944 code (loss of pump prime). Did some reading and it could be clogged filters, a split main filter, or a loose spin on filter (this trans has 2 filters, one main flat one and the other spin on is for the cooler return circuit. First I used my vacuum oil changer to pull out as much ATF as I could out of the pan to minimize the mess (no drain plug on the pan). I removed the pan (15 8mm bolts, some I had to use a socket with a built in ujoint because of limited clearance around the cat converter and exhaust pipe.
The pan was clean, not much wear particles on the magnet. The filters looked good but when I went to remove the spin on, it wasn't tight, not like an oil filter usually is. I removed both filters, replaced the seal for the main filter in the trans case, and reinstalled both making sure the spin on was good and snug. Cleaned the pan, removed all the RTV and re-applied Chrysler auto trans RTV. Bolted it up and let it cure overnight. Filled it up with 8 qts of ATF+4 and it went into gear! I was thinking I needed a new trans but apparently this is not real common but it can happen. Current mileage is 120,000 miles and shifting fine. Just wanted to pass this along, if anyone had the same problem. Same transmission is used in Dodge/Ram 1500 trucks and some older Liberty Diesels.