Vehicle Speed Signal Circuit between Radio Receiver and Combination Meter: Description

WARNING: This page is about a different car, the 2009 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.

The circuit is necessary for the ASL (Automatic Sound Levelizer) built into the radio receiver.

Speed signals are received from the combination meter and used for the ASL.

The ASL function automatically adjusts the sound volume in order to enable clear audio quality even when vehicle noise increases (as vehicle noise increases, the volume is turned up etc.).

HINT:

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