Lexus RX (RX 350L, RX450h) 2016-2024 Repair Manual: Speed Signal Circuit

DESCRIPTION

The combination meter assembly receives the vehicle speed signal from this circuit. The wheel speed sensors produce an output that varies according to the vehicle speed. The wheel speed sensor output is received by the brake actuator assembly (skid control ECU) which uses this information to create the vehicle speed signal*a. The vehicle speed signal consists of pulses sent to the combination meter assembly from the brake actuator assembly (skid control ECU). To create this signal, 12 V is output from IG2 which is behind a resistor in the combination meter assembly. This voltage is sent to the brake actuator assembly (skid control ECU). The pulse signal is created by switching the transistor in the brake actuator assembly (skid control ECU) on and off, making the voltage on the wire drop to 0 V. A similar system is used for the output of this signal from the combination meter assembly via terminal +S. A voltage of 12 V or 5 V is applied to terminal +S from each ECU or relay that is connected to this terminal. The transistor in the combination meter assembly is controlled by the signal from the brake actuator assembly (skid control ECU). When this transistor is turned on, this transistor makes the voltage supplied by the various ECUs (via their respective internal resistors) drop to 0 V. Each ECU connected to terminal +S of the combination meter assembly controls its respective system based on this pulse signal.

HINT:

This circuit is used for the systems connected to terminal +S. This signal is not used for combination meter assembly operation. Combination meter assembly components such as the speedometer operate using data received via CAN communication.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

PROCEDURE

(a) Disconnect the J10 combination meter assembly connector.

*a Front view of wire harness connector (to Combination Meter Assembly)

(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 supplies power to the combination meter assembly, the combination meter assembly will output a waveform.

NG

GO TO STEP 5

OK

(a) Reconnect the J10 combination meter assembly connector.

(b) Disconnect the A41 brake actuator assembly (skid control ECU) connector.

*a Front view of wire harness connector (to Brake Actuator Assembly (Skid Control ECU))

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

Standard Voltage:

NG

GO TO STEP 4

OK

(a) Check the input waveform. (1) Reconnect the A41 brake actuator assembly (skid control ECU) connector. (2) Remove the combination meter assembly with the connector(s) still connected. (3) Connect an oscilloscope to terminal J10-20 (SI) and body ground. (4) Turn the engine switch on (IG). (5) Turn a wheel slowly. (6) Check the signal waveform according to the condition(s) in the table below. Item Condition Tool setting 5 V/DIV., 20 ms./DIV. Vehicle condition Engine switch on (IG), wheel being rotated 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.

*a Component with harness connected (Combination Meter Assembly)

OK

REPLACE COMBINATION METER ASSEMBLY

NG

REPLACE BRAKE ACTUATOR ASSEMBLY (SKID CONTROL ECU)

(a) Disconnect the J10 combination meter assembly connector.

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

Standard Resistance:

OK

REPLACE COMBINATION METER ASSEMBLY

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

(a) Disconnect the J102 junction connector.

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

Standard Resistance:

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

(a) Check for a short in the wire harness and connectors connected to the junction connector shown in the wiring diagram.

HINT:

If voltage is not present, it is possible that an ECU or circuit has a malfunction. The malfunctioning ECU or circuit will be diagnosed in the following steps.

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

Standard Voltage:

B

REPLACE JUNCTION CONNECTOR (INSTRUMENT PANEL WIRE)

A

(a) Select the circuit for which voltage was not present in step 6.

B

GO TO STEP 9

C

GO TO STEP 10

D

GO TO STEP 11

E

GO TO STEP 12

A

(a) Disconnect the A37 ECM connector.

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

Standard Resistance:

OK

REPLACE ECM

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

(a) Disconnect the J41 certification ECU (smart key ECU assembly) connector.

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

Standard Resistance:

OK

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

(a) Disconnect the J148 radio receiver assembly connector.

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

Standard Resistance:

OK

REPLACE RADIO RECEIVER ASSEMBLY

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

(a) Disconnect the J66*1 or J156*2 stereo component amplifier assembly connector.

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

Standard Resistance:

OK

REPLACE STEREO COMPONENT AMPLIFIER ASSEMBLY

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

(a) Disconnect the J153 navigation ECU connector.

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

Standard Resistance:

OK

REPLACE NAVIGATION ECU

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR