Vehicle Speed Signal Circuit between Radio Receiver and Combination Meter [06/2020 - 10/2022]: Description

This circuit is necessary for the Automatic Sound Levelizer (ASL) built into the radio and display receiver assembly.

The Automatic Sound Levelizer (ASL) function automatically adjusts the audio system volume in order to compensate for increased vehicle noise (vehicle noise tends to increase as vehicle speed increases). The ASL adjusts the volume based on vehicle speed signals sent from the combination meter assembly.

HINT: 

• A voltage of 12 V or 5 V is output from each ECU and then input to the combination meter assembly. The signal is changed to a pulse signal at the transistor in the combination meter assembly. Each ECU controls its respective system based on this pulse signal.
• If a short occurs in any of the ECUs or in the wire harness connected to an ECU, all systems in the following diagram will not operate normally.