If the tweeters are working then the radio is not the problem. The tweeters and front door speakers are on the same circuit so if the tweeters are getting a signal then the other speakers should be getting a signal. Its not uncommon for the stock speakers to go bad. If you have a ohm meter (multimeter) then you can check the speakers. Measure across the 2 wires at the speakers with the speakers disconnected. You should measure about 4 ohms. If there is no reading or higher reading then 4, the speakers are bad. I would get a good set of after market speakers to replace them, they are about the same price as the stock ones from the dealer and they sound much better.