AUDIO AND VISUAL SYSTEM (for Radio Receiver Type) Vehicle Speed Signal Circuit between Radio Receiver and Combination Meter

DESCRIPTION

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

The 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.

Tech Tips


  • 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 diagram below will not operate normally.

WIRING DIAGRAM

A003UYAE03

INSPECTION PROCEDURE

PROCEDURE


  1. INSPECT COMBINATION METER ASSEMBLY (OUTPUT WAVE FORM)


    1. A003T12E48
      Text in Illustration
      *a

      Component with harness connected

      (Combination Meter Assembly)

      Check the output waveform.


      1. Remove the combination meter assembly with the connector still connected.

      2. Connect an oscilloscope to terminal E46-36 (+S) and body ground.

      3. Turn the power switch on (IG).

      4. Turn a wheel slowly.

      5. Check the signal waveform according to the condition(s) in the table below.

        Item Condition
        Tool setting 5 V/DIV., 20 ms./DIV.
        Vehicle condition Wheel being rotated
        OK
        The waveform is similar to that shown in the illustration.

        Tech Tips

        When the system is functioning normally, one wheel revolution generates 4 pulses. As the vehicle speed increases, the width indicated by (A) in the illustration narrows.


    NG

    GO TO METER / GAUGE SYSTEM Click here

    OK

  2. CHECK HARNESS AND CONNECTOR (RADIO RECEIVER ASSEMBLY - COMBINATION METER ASSEMBLY)


    1. Disconnect the radio receiver assembly connector and combination meter assembly connector.

    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance
      Tester Connection Condition Specified Condition
      E26-3 (SPD) - E46-36 (+S) Always Below 1 Ω

    NG

    REPLACE RADIO RECEIVER ASSEMBLY Click here

    OK

  3. CHECK HARNESS AND CONNECTOR (RADIO RECEIVER ASSEMBLY - NO. 4 JUNCTION BLOCK)


    1. Disconnect the No. 4 junction block connector.

    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance
      Tester Connection Condition Specified Condition
      4A-20 - E26-3 (SPD) Always Below 1 Ω

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (RADIO RECEIVER ASSEMBLY - NO. 4 JUNCTION BLOCK)

    OK

    REPAIR OR REPLACE HARNESS OR CONNECTOR (NO. 4 JUNCTION BLOCK)