Vehicle Speed Signal Circuit between Stereo Component Amplifier and Combination Meter

AUDIO / VIDEO: AUDIO AND VISUAL 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 (No. 3 meter circuit plate) and used for the ASL.

The ASL function automatically adjusts the sound volume in order to clear audio quality even when vehicle noise increases (as vehicle noise increases, the volume is turned up etc.).

HINT
* A voltage of 12 V or 5 V is output from each ECU and then input to the combination meter assembly (No. 3 meter circuit plate). The signal is changed to a pulse signal at the transistor in the combination meter assembly (No. 3 meter circuit plate). 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. INSPECT COMBINATION METER ASSEMBLY (No. 3 meter circuit plate (OUTPUT WAVEFORM))

(a) Check the output waveform.

(1) Remove the combination meter assembly (No. 3 meter circuit plate) with the connector still connected.

(2) Connect an oscilloscope to terminal L27-7 (+S) and body ground.

(3) Turn the power switch on (IG).

(4) Turn the wheel slowly.

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

OK:

The waveform is displayed as 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 -- GO TO METER / GAUGE SYSTEM Speed Signal Circuit
OK -- Continue to next step.

2. CHECK HARNESS AND CONNECTOR

(a) Disconnect the stereo component amplifier assembly and combination meter assembly (No. 3 meter circuit plate) connectors.

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

Standard Resistance:

Text in Illustration

NG -- CHECK HARNESS AND CONNECTOR (STEREO COMPONENT AMPLIFIER ASSEMBLY - NO. 4 JUNCTION BLOCK)

OK -- REPLACE STEREO COMPONENT AMPLIFIER ASSEMBLY Removal

3. CHECK HARNESS AND CONNECTOR (STEREO COMPONENT AMPLIFIER ASSEMBLY - NO. 4 JUNCTION BLOCK)

(a) Disconnect the stereo component amplifier assembly connector.

(b) Disconnect the No. 4 junction block connector.

Text in Illustration

NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (STEREO COMPONENT AMPLIFIER ASSEMBLY - NO. 4 JUNCTION BLOCK)
OK -- Continue to next step.

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

(a) Disconnect the No. 4 junction block connector.

(b) Disconnect the No. 3 junction block connector.

Text in Illustration

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

5. CHECK HARNESS AND CONNECTOR (NO. 3 JUNCTION BLOCK - COMBINATION METER ASSEMBLY)

(a) Disconnect the No. 3 junction block connector.

(b) Disconnect the combination meter assembly (No. 3 meter circuit plate) connector.

Text in Illustration

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

6. INSPECT NO. 4 JUNCTION BLOCK

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

Standard Resistance:

Text in Illustration

NG -- REPLACE NO. 4 JUNCTION BLOCK
OK -- Continue to next step.

7. INSPECT NO. 3 JUNCTION BLOCK

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

Standard Resistance:

Text in Illustration

NG -- REPLACE NO. 3 JUNCTION BLOCK

OK -- REPLACE STEREO COMPONENT AMPLIFIER ASSEMBLY Removal