Vehicle Speed Signal Circuit Between Stereo Component Amplifier And Combination Meter

AUDIO / VIDEO: AUDIO AND VISUAL SYSTEM (W/O Navigation System): Vehicle Speed Signal Circuit between Stereo Component Amplifier and Combination Meter
- Vehicle Speed Signal Circuit between Stereo Component Amplifier and Combination Meter

DESCRIPTION

The circuit is necessary for the Automatic Sound Levelizer (ASL) built into the stereo component amplifier assembly.

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

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.

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.
WIRING DIAGRAM





INSPECTION PROCEDURE

PROCEDURE

1. CHECK HARNESS AND CONNECTOR

(a) Disconnect the stereo component amplifier assembly connector.





(b) Disconnect the combination meter assembly connector.





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

Standard Resistance:





Text in Illustration





NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.

2. INSPECT COMBINATION METER ASSEMBLY (OUTPUT WAVEFORM)

(a) Reconnect the combination meter assembly connector.

(b) Check the output waveform.





(1) Connect an oscilloscope to terminal P30-11 (SPD) and body ground.

(2) Turn the engine switch on (IG).

(3) Turn a wheel slowly.

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









OK:

The waveform is similar to that shown in the illustration.

HINT
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.

Text in Illustration





NG -- REPLACE COMBINATION METER ASSEMBLY Removal

OK -- REPLACE STEREO COMPONENT AMPLIFIER ASSEMBLY Removal