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

DESCRIPTION

While the engine is being cranked, current flows from terminal STAR of the certification ECU (smart key ECU assembly) to the park/neutral position switch assembly and to terminal STA of the ECM (STA signal).

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Inspect the fuses for circuits related to this system before performing the following procedure.

PROCEDURE

1.

CHECK WHETHER ENGINE CAN BE CRANKED

(a) Check if the engine can be cranked.

Result

Proceed to

Engine cannot be cranked

A

Engine can be cranked

B

B

GO TO STEP 12

A

2.

READ VALUE USING TECHSTREAM (STARTER SW)

(a) Connect the Techstream to the DLC3.

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

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine / Data List / Starter SW.

Powertrain > Engine > Data List

Tester Display

Starter SW

(e) Check the value displayed on the Techstream when the engine switch is turned on (IG) and the engine is cranked.

OK:

Condition

Techstream Display (Starter SW)

Engine switch on (IG)

OFF

Cranking position

ON

NG

GO TO STEP 9

OK

3.

INSPECT RELAY (ST RELAY)

(a) Inspect the ST relay.

Click here

NG

REPLACE RELAY (ST RELAY)

OK

4.

INSPECT STARTER ASSEMBLY

(a) Inspect the starter assembly.

Click here

NG

REPLACE STARTER ASSEMBLY

OK

5.

CHECK HARNESS AND CONNECTOR (ST RELAY - STARTER ASSEMBLY)

(a) Remove the ST relay from the engine room relay block and junction block assembly.

(b) Disconnect the starter assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

3 (ST relay) - D21-1 (ST)

Always

Below 1 Ω

3 (ST relay) or D21-1 (ST) - Body ground and other terminals

Always

10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

6.

CHECK HARNESS AND CONNECTOR (ST RELAY - BODY GROUND)

(a) Remove the ST relay from the engine room relay block and junction block assembly.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

1 (ST relay) - Body ground

Always

Below 1 Ω

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

7.

CHECK HARNESS AND CONNECTOR (PARK/NEUTRAL POSITION SWITCH ASSEMBLY - CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) - ST RELAY)

(a) Disconnect the park/neutral position switch assembly connector.

(b) Disconnect the certification ECU (smart key ECU assembly) connector.

(c) Remove the ST relay from the engine room relay block and junction block assembly.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

D15-9 (L) - 2 (ST relay)

Always

Below 1 Ω

A74-20 (STA) - 2 (ST relay)

Always

Below 1 Ω

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

8.

CHECK HARNESS AND CONNECTOR (BATTERY - ST RELAY)

(a) Remove the ST relay from the engine room relay block and junction block assembly.

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

5 (ST relay) - Body ground

Always

11 to 14 V

OK

REPAIR OR REPLACE HARNESS OR CONNECTOR (BATTERY - STARTER ASSEMBLY)

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

9.

INSPECT PARK/NEUTRAL POSITION SWITCH ASSEMBLY

(a) Inspect the park/neutral position switch assembly.

  • for 2WD models: Click here
  • for AWD models: Click here
NG

REPLACE PARK/NEUTRAL POSITION SWITCH ASSEMBLY

OK

10.

CHECK HARNESS AND CONNECTOR (PARK/NEUTRAL POSITION SWITCH ASSEMBLY - ECM - ST RELAY - CERTIFICATION ECU (SMART KEY ECU ASSEMBLY))

(a) Disconnect the park/neutral position switch assembly connector.

(b) Disconnect the ECM connector.

(c) Remove the ST relay from the engine room relay block and junction block assembly.

(d) Disconnect the certification ECU (smart key ECU assembly) connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

D15-9 (L) - A37-43 (STA)

Always

Below 1 Ω

D15-9 (L), A37-43 (STA), 2 (ST relay) or A74-20 (STA) - Body ground and other terminals

Always

10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

11.

CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) - PARK/NEUTRAL POSITION SWITCH ASSEMBLY - ECM)

(a) Disconnect the park/neutral position switch assembly connector.

(b) Disconnect the certification ECU (smart key ECU assembly) connector.

(c) Disconnect the ECM connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

A74-9 (STAR) - D15-4 (B)

Always

Below 1 Ω

A74-9 (STAR) - D2-106 (NSW)

Always

Below 1 Ω

A74-9 (STAR), D15-4 (B) or D2-106 (NSW) - Body ground and other terminals

Always

10 kΩ or higher

OK

GO TO SMART ACCESS SYSTEM WITH PUSH-BUTTON START

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

12.

READ VALUE USING TECHSTREAM (STARTER SW)

(a) Connect the Techstream to the DLC3.

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

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine / Data List / Starter SW.

Powertrain > Engine > Data List

Tester Display

Starter SW

(e) Check the value displayed on the Techstream when the engine switch is turned on (IG) and the engine is cranked.

OK:

Condition

Techstream Display (Starter SW)

Engine switch on (IG)

OFF

Cranking position

ON

OK

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR (ST RELAY - ECM)

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