There is a couple of ways you can trouble shoot this, first thing check the obvious:
Take out the drivers side speaker and test it with an Ohm meter. It should register the rated impedence printed on the speaker magnet if its not listed, I can't remember if it is or not, then the speaker should range anywhere from 2-8 Ohm's. If your reading is in that range the speaker is good then its an amp issue (see below). If it reads as a short or some odd range like 150 ohms then the speaker is toast and needs replaced.
Next obvious issue is the amp which means you gotta go fishing under the dash. You have to remove your glovebox to get to the amp for the main cab speakers. Once you get access to the grey box mounted to a crossmember brace directly behind the glove box check to make sure all the harnesses are plugged in all the way into the amp. One of those harnesses goes to the amp under the center arm rest for the sub signal. If you find a loose harness then try it all out with a turn of the key and see if your sound is back.
If the drivers side speaker was found to be blown then its possible the sub is blown too. Here you would just pull the speaker assembly and find the factory quick disconnect, which is behind the sub assembly on an RC and have no clue for a QC, and test it there with an ohm meter and the same numbers from above would apply.
If I was a betting man I would bet the amp under the dash is bad and needs replacing. Of course check the obvious and easy first.
If you have it under warranty still then take it to dodge and let there monkeys try to figure it out, just ask if you can watch while you sip on a soda.
If you need any more help just PM me and we can take it offline. Cheers!
