Vehicle Speed Signal Circuit between Stereo Component Amplifier and Combination Meter: Description
WARNING: This page is about a different car, the 2009 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.
This circuit is necessary for the ASL (Auto Sound Levelizer) built into the stereo component amplifier. Speed signals are received from the combination meter and used for the ASL.
The ASL function automatically adjusts the sound data in order to enable hearing the clear audio even when vehicle noise increases (as vehicle noise increases, the volume is turned up, etc.).