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.).
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.
INSPECT COMBINATION METER ASSEMBLY (OUTPUT WAVEFORM)
Component with harness connected
(Combination Meter Assembly)
Check the output waveform.
Remove the combination meter assembly with the connector still connected.
Connect an oscilloscope to terminals F1-6 (+S) and body ground.
Turn the ignition switch to ON.
Turn the wheel slowly.
Check the signal waveform according to the condition(s) in the table below.
|Tool setting||5 V/DIV., 20 ms./DIV.|
|Vehicle condition||Driving at approx. 20 km/h (12 mph)|
|The waveform is displayed as shown in the illustration.|
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.
GO TO METER / GAUGE SYSTEM Click here
CHECK HARNESS AND CONNECTOR (RADIO RECEIVER ASSEMBLY - COMBINATION METER ASSEMBLY)
Disconnect the F47 radio receiver connector and the combination meter assembly connector.
Disconnect the F1 combination meter assembly connector.
Measure the resistance according to the value(s) in the table below.
|Standard Resistance (Check for Open)|
|Standard Resistance (Check for Short)|
REPLACE RADIO RECEIVER ASSEMBLY Click here
REPAIR OR REPLACE HARNESS OR CONNECTOR