I did the check and, lo and behold, the sub woofer/amp is dead as a door nail.
I tried to remove the grille but it seems that I have to take off the entire side panel in the cargo area.
Before I spend hundreds of dollars to have the head unit repaired I'd rather buy a new one, which I had planned anyway.
I just haven't found the one I'm looking for, there are too many in the marketplace.
Again, thanks for all your input.
Ed