AUDIO AND VISUAL SYSTEM(for Radio Receiver Type) Vehicle Speed Signal Circuit between Radio Receiver and Combination Meter
DESCRIPTION
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This circuit is necessary for the Automatic Sound Levelizer (ASL) built into the radio receiver assembly.
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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.
Tech Tips
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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.
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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.
WIRING DIAGRAM
PROCEDURE
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INSPECT COMBINATION METER ASSEMBLY (OUTPUT WAVEFORM)
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Check the output waveform.
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Remove the combination meter assembly with the connector still connected.
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Connect an oscilloscope to terminals F1-6 (+S) and body ground.
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Turn the ignition switch ON (IG).
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Turn the wheel slowly.
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Check the signal waveform according to the condition(s) in the table below.
Item Condition Measurement terminal F1-6 (+S) - Body ground Tool setting 5 V/DIV., 20 ms./DIV. Vehicle condition Wheel being rotated Text in Illustration *a Component with harness connected
(Combination Meter Assembly)
OK The waveform is displayed as 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.
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NG 
GO TO METER / GAUGE SYSTEM Click here
OK 
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CHECK HARNESS AND CONNECTOR (RADIO RECEIVER ASSEMBLY - COMBINATION METER ASSEMBLY)
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Disconnect the F32 radio receiver assembly connector.
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Disconnect the F1 combination meter assembly connector.
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Measure the resistance according to the value(s) in the table below.
Standard Resistance Tester Connection Condition Specified Condition F32-17 (SPD) - F1-6 (+S) Always Below 1 Ω F32-17 (SPD) - Body ground Always 10 kΩ or higher
OK
REPLACE RADIO RECEIVER ASSEMBLY Click here
NG
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CHECK HARNESS AND CONNECTOR (RADIO RECEIVER ASSEMBLY - JUNCTION CONNECTOR)
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Disconnect the F32 radio receiver assembly connector.
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Disconnect the 3A junction connector.
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Measure the resistance according to the value(s) in the table below.
Standard Resistance Tester Connection Condition Specified Condition F32-17 (SPD) - 3A-16 Always Below 1 Ω
OK
REPAIR OR REPLACE HARNESS OR CONNECTOR (JUNCTION CONNECTOR)
NG
REPAIR OR REPLACE HARNESS OR CONNECTOR (RADIO RECEIVER ASSEMBLY - JUNCTION CONNECTOR)
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