Lexus NX: ECM Power Source Circuit
DESCRIPTION
When the power switch is turned on (IG), auxiliary battery voltage is applied to the IGSW terminal of the ECM. The output signal from the MREL terminal of the ECM causes current to flow to the coil of the EFI-MAIN relay, closing the contacts of the EFI-MAIN relay and supplying power to terminals +B and +B2 of the ECM.
WIRING DIAGRAM
CAUTION / NOTICE / HINT
NOTICE:
Inspect the fuses for circuits related to this system before performing the following procedure.
PROCEDURE
| 1. | CHECK HARNESS AND CONNECTOR (IG2-MAIN RELAY VOLTAGE) |
| *1 | No. 1 Engine Room Relay Block and Junction Block Assembly |
| *2 | IG2-MAIN Relay |
(a) Remove the IG2-MAIN relay from the No. 1 engine room relay block and junction block assembly.
(b) Turn the power switch on (IG).
(c) Measure the voltage according to the value(s) in the table below.
Standard Voltage:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| 1 (IG2-MAIN relay) - Body ground | Power switch on (IG) | 11 to 14 V |
| NG | .gif) | GO TO STEP 11 |
|
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| 2. | INSPECT IG2-MAIN RELAY |
(a) Inspect the IG2-MAIN relay.
Click here .gif)
| NG | | REPLACE IG2-MAIN RELAY |
|
| 3. | CHECK HARNESS AND CONNECTOR (AUXILIARY BATTERY - IG2-MAIN RELAY) |
| *1 | No. 1 Engine Room Relay Block and Junction Block Assembly |
| *2 | IG2-MAIN Relay |
(a) Remove the IG2-MAIN relay from the No. 1 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 |
|---|---|---|
| 3 (IG2-MAIN relay) - Body ground | Always | 11 to 14 V |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 4. | CHECK HARNESS AND CONNECTOR (IG2-MAIN RELAY - BODY GROUND) |
(a) Remove the IG2-MAIN relay from the No. 1 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 |
|---|---|---|
| 2 (IG2-MAIN relay) - Body ground | Always | Below 1 Ω |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 5. | CHECK HARNESS AND CONNECTOR (IG2-MAIN RELAY - ECM) |
(a) Remove the IG2-MAIN relay from the No. 1 engine room relay block and junction block assembly.
(b) Disconnect the ECM connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| 5 (IG2-MAIN relay) - A35-37 (IGSW) | Always | Below 1 Ω |
| 5 (IG2-MAIN relay) or A35-37 (IGSW) - Body ground | Always | 10 kΩ or higher |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 6. | INSPECT EFI-MAIN RELAY |
(a) Inspect the EFI-MAIN relay.
Click here
| NG | | REPLACE EFI-MAIN RELAY |
|
| 7. | CHECK HARNESS AND CONNECTOR (AUXILIARY BATTERY - EFI-MAIN RELAY) |
| *1 | No. 1 Engine Room Relay Block and Junction Block Assembly |
| *2 | EFI-MAIN Relay |
(a) Remove the EFI-MAIN relay from the No. 1 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 (EFI-MAIN relay) - Body ground | Always | 11 to 14 V |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 8. | CHECK HARNESS AND CONNECTOR (EFI-MAIN RELAY - BODY GROUND) |
(a) Remove the EFI-MAIN relay from the No. 1 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 |
|---|---|---|
| 2 (EFI-MAIN relay) - Body ground | Always | Below 1 Ω |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 9. | CHECK HARNESS AND CONNECTOR (EFI-MAIN RELAY - ECM) |
(a) Remove the EFI-MAIN relay from the No. 1 engine room relay block and junction block assembly.
(b) Disconnect the ECM connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| 3 (EFI-MAIN relay) - A35-2 (+B) | Always | Below 1 Ω |
| 3 (EFI-MAIN relay) - A35-3 (+B2) | Always | Below 1 Ω |
| 1 (EFI-MAIN relay) - A35-46 (MREL) | Always | Below 1 Ω |
| 3 (EFI-MAIN relay) or A35-2 (+B) - Body ground | Always | 10 kΩ or higher |
| 3 (EFI-MAIN relay) or A35-3 (+B2) - Body ground | Always | 10 kΩ or higher |
| 1 (EFI-MAIN relay) or A35-46 (MREL) - Body ground | Always | 10 kΩ or higher |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 10. | CHECK HARNESS AND CONNECTOR (ECM - BODY GROUND) |
(a) Disconnect the ECM connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| C48-16 (E1) - Body ground | Always | Below 1 Ω |
| OK | | PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
| 11. | CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) - IG2-MAIN RELAY) |
(a) Disconnect the Certification ECU (smart key ECU assembly) connector.
(b) Remove the IG2-MAIN relay from the No. 1 engine room relay block and junction block assembly.
(c) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| I51-3 (IG1D) - 1 (IG2-MAIN relay) | Always | Below 1 Ω |
| OK | | GO TO SMART ACCESS SYSTEM WITH PUSH-BUTTON START |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
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