Speed Signal Circuit

METER: METER / GAUGE SYSTEM: Speed Signal Circuit

Speed Signal Circuit

DESCRIPTION

The meter CPU receives vehicle speed signals from this circuit. The vehicle speed sensor detects the voltage that varies according to the vehicle speed. The skid control ECU supplies power to the vehicle speed sensor. The skid control ECU detects vehicle speed signals based on the pulses of the voltage. The skid control ECU transmits vehicle speed signals as pulses to the meter CPU. A voltage of 12 V is output from the combination meter assembly and then input to the skid control ECU. The signal is changed to a pulse signal at the transistor in the combination meter assembly.
A voltage of 12 V or 5 V is output from each ECU or relay and then input to the combination meter assembly.
Each ECU controls the respective system based on the pulse signal.

HINT: This circuit is used for another system, and is not used for combination meter operation.

WIRING DIAGRAM





INSPECTION PROCEDURE

PROCEDURE

1. INSPECT COMBINATION METER ASSEMBLY (OUTPUT WAVEFORM)





(a) Check the output waveform.
(1) Remove the combination meter assembly with connector(s) still connected.
(2) Connect the oscilloscope to the terminals F2-12 (+S) and body ground.
(3) Turn the ignition 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: As the vehicle speed increases, the cycle of the waveform narrows.

NG -- INSPECT ECU TERMINAL VOLTAGE (INPUT VOLTAGE)
OK -- RETURN TO THE ORIGINAL INSPECTION FOR OTHER SYSTEM
2. INSPECT ECU TERMINAL VOLTAGE (INPUT VOLTAGE)





(a) Disconnect the F2 connector.
(b) Measure the voltage according to the value(s) in the table below.

Standard voltage:





HINT: If any of the ECUs specified in the wiring diagram supplied power to the combination meter, the combination meter will output a waveform.

NG -- CHECK HARNESS AND CONNECTOR (COMBINATION METER - NO. 3 JUNCTION BLOCK)
OK -- Continue to next step.
3. INSPECT COMBINATION METER ASSEMBLY (OUTPUT VOLTAGE)





(a) Disconnect the A74 connector.
(b) Measure the voltage according to the value(s) in the table below.

Standard voltage:





NG -- CHECK HARNESS AND CONNECTOR (COMBINATION METER - SKID CONTROL ECU)
OK -- Continue to next step.
4. INSPECT SKID CONTROL ECU (INPUT WAVEFORM)





(a) Check the input waveform.
(1) Reconnect the A74 connector.
(2) Remove the combination meter assembly with connector(s) still connected.
(3) Connect the oscilloscope to the terminals F2-14 (SI) and body ground.
(4) Power switch on (IG).
(5) Turn the wheel slowly.
(6) Check the signal waveform according to the condition(s) in the table below.





OK:
The waveform is displayed as shown in the illustration.

HINT: As the vehicle speed increases, the cycle of the waveform narrows.

NG -- REPLACE SKID CONTROL ECU
OK -- REPLACE COMBINATION METER ASSEMBLY
5. CHECK HARNESS AND CONNECTOR (COMBINATION METER - NO. 3 JUNCTION BLOCK)
(a) Disconnect the A No. 3 junction block connector.





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

Standard resistance:





NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
6. CHECK HARNESS AND CONNECTOR (NO. 3 JUNCTION BLOCK)
(a) Inspect for a short in the circuit that connected the No. 3 junction block shown in the wiring diagram.

HINT: If voltage is not present, the circuit (ECU) was possibly the malfunctioning circuit. This is the circuit that will be diagnosed by following the A step that follows.

(1) Disconnect the B and C No. 3 junction block connectors.





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

Standard voltage:





(3) Reconnect the C No. 3 junction block connectors.





(4) Measure the voltage according to the value(s) in the table below.

Standard voltage:





*1: without Navigation System
*2: with Navigation System

Result:





B -- REPAIR OR REPLACE HARNESS OR CONNECTOR (NO. 3 JUNCTION BLOCK)
A -- Continue to next step.
7. CHECK HARNESS AND CONNECTOR (NO. 3 JUNCTION BLOCK - MALFUNCTIONING CIRCUIT)
(a) Disconnect the ECU connector that is possibly the malfunctioning.





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

Standard resistance:





*1: without Navigation System
*2: with Navigation System

HINT: If an inspected wire harness is connected to another junction connector or junction block, perform the same inspection for the junction connector or junction block on the ECU side.

NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE MALFUNCTIONING ECU
8. CHECK HARNESS AND CONNECTOR (COMBINATION METER - SKID CONTROL ECU)





(a) Disconnect the F2 connector.
(b) Measure the resistance according to the value(s) in the table below.

Standard resistance:





NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE COMBINATION METER ASSEMBLY