GM Parts Direct: 10395208 - AMPLIFIER
Looking for a price lower than that?
If you wanted to diagnose the system you'd need a multimeter at the very least.
Check for signal coming out of the amp to the speakers. If you have signal there, check at the speakers. If not, wiring issue.
If you didn't have signal at the amp, check the input to the amp.
If no, check the radio. If yes, likely an issue with the amp.
I'm inclined to agree with the above post: Investigate the possibility of a damaged speaker/driver.
