Lexus RX (RX 350L, RX450h) 2016-2026 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
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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 | .gif) | GO TO STEP 12 |
|
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| 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 |
|
| 3. | INSPECT RELAY (ST RELAY) |
(a) Inspect the ST relay.
Click here .gif)
| NG | | REPLACE RELAY (ST RELAY) |
|
| 4. | INSPECT STARTER ASSEMBLY |
(a) Inspect the starter assembly.
Click here
| NG | | REPLACE STARTER ASSEMBLY |
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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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Lexus RX (RX 350L, RX450h) 2016-{YEAR} Owners Manual
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Lexus RX (RX 350L, RX450h) 2016-{YEAR} Repair Manual
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