Lost sound on 2005 impala. radio works. seems like amp problem.

Do you have base or up;level system ?

Table 1: Radio Features
Table 2: Cassette Features
Table 3: Compact Disc Features
Table 4: XM Advisory Messages
The radio receives power from the RADIO fuse in the junction block-right I/P. Ground is provided via G201 and G202. The radio is enabled/disabled by class 2 messages from the body control module (BCM). The radio routes audio signals from the digital radio receiver or the vehicle communication interface module (VCIM) to the speakers and/or amplifier when directed by class 2 messages.
The Entertainment System on this vehicle is configured with an AM/FM stereo radio with the radio data system (RDS) and either a cassette player or a CD player or both. CD and cassette. The uplevel system provides the customer with extended range speakers and an audio amplifier. Satellite digital radio (U2K) is available with uplevel systems.
The following list shows the radios available for this vehicle:
• Radio (ULO) - AM/FM Stereo, Cassette with RDS
• Radio (UNO) - AM/FM Stereo, CD and RDS
• Radio (UPO) - AM/FM Stereo, Cassette with CD and RDS .The complexity of the radio systems on these vehicle is mind blowing .

Your best bet take it to a GM dealer , has features you are unawear of .
DTC B1025, B1035, B1045, or B1055
When the radio is powered up, the radio supplies low level audio signals to the speakers. If the vehicle is equipped with an audio amplifier, the amplifier will boost the signal sent to the speakers.
DTC B1025 Audio Output Circuit
Install a scan tool.
Turn ON the ignition, with the engine OFF.
With the scan tool, monitor the DTC Information for DTC B1025.
Does the scan tool indicate that DTC B1025 is current?

If you have no sound then the radio doesn't work, are you sure you have an amplifier in the car separate from the radio, if not the radio needs to be tested and repaire. GM makes a special tool to bypass the amplifier for testing I am told.