SCV (Speed-Compensated Volume) Control
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
The SCV (Speed-Compensated Volume) ring is located behind the PWR-VOL control knob. Rotating the ring up or down will automatically cause the volume to raise and lower as the speed of the vehicle increases and decreases. The top position has a higher maximum volume. The top position gets louder faster than the lower positions. When the system is ON the SCV will display. Rotating the ring all the way down will turn the SCV system OFF. Subtle changes in volume should not be noticeable to the driver when the system is working properly.