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

for Automatic Sound Levelizer (ASL): 

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

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

for "Bluetooth": 

• Speed signals are received from the combination meter assembly and used to cancel "Bluetooth" function operation.

  The radio receiver assembly recognizes that the vehicle is being driven and makes it impossible to connect or register a "Bluetooth" device while driving.

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 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 following diagram will not operate normally.