First question is if you ever spilled a soft drink into the radio such that the AM/FM/SAT switch gets sticky?
2nd, do you have any way to pull-out the radio and borrow a magnetic-mount Sirius antenna to temporarily test and see if the antenna on the vehicle is bad?
If passing the first two tests, then it's likely the whole radio unit has to be replaced with a model from a similar year. Actually, the audio quality you get from an XM Onyx will be much better than the Sirius radio in the Chrysler vehicles, and you can just use the AUX input on the radio for playback.