Problem with Satellite radiio

I have the Sirius Satellite radio (REN) in my van. (Non GPS). Every once in a while, it will go into "lost signal mode" and stay there until I turn off the engine and restart it. Just turning the radio on and off doesn't fix it. This is not the usual brief signal loss mode due to buildings or whatever. Any ideas? The AM & FM continue to work fine when the Sirius is down. TIA