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ECU Power Source Circuit [08/2023 - ]: Procedure

WARNING: This page is about a different car, the 2025 Lexus RX 450h+ and 2024 Lexus RX 450h+. However, it is still accessible from the selected car via links, so may be relevant.
  1. CHECK HYBRID VEHICLE CONTROL ECU ASSEMBLY (+B1, +B2 VOLTAGE) 
    1. Turn the ignition switch to ON.
    2. Measure the voltage according to the value(s) in the table below.
      GTY1204385Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Hybrid Vehicle Control ECU)      		 - -

      Standard Voltage

      Tester Connection Condition Specified Condition
      C59-8 (+B1) - Body ground Ignition switch ON 11 to 14 V
      A21-10 (+B2) - Body ground Ignition switch ON 11 to 14 V
    3. Turn the ignition switch off.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  3

    Result: 

    OK 

    See step  2

  2. CHECK HARNESS AND CONNECTOR (HYBRID VEHICLE CONTROL ECU - BODY GROUND) 
    1. Disconnect the hybrid vehicle control ECU connectors.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      C59-1 (E1) - Body ground Always Below 1 Ω
      A21-12 (E01) - Body ground Always Below 1 Ω
      A21-24 (E12) - Body ground Always Below 1 Ω
    3. Reconnect the hybrid vehicle control ECU connectors.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    GO TO PROBLEM SYMPTOMS TABLE. Refer to  PROBLEM SYMPTOMS TABLE [08/2023 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  3. CHECK HYBRID VEHICLE CONTROL ECU ASSEMBLY (MREL VOLTAGE) 
    1. Turn the ignition switch to ON.
    2. Measure the voltage according to the value(s) in the table below.
      GTY1205900Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Hybrid Vehicle Control ECU)      		 - -

      Standard Voltage

      Tester Connection Condition Specified Condition
      C59-10 (MREL) - Body ground Ignition switch ON 11 to 14 V
    3. Turn the ignition switch off.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE HYBRID VEHICLE CONTROL ECU ASSEMBLY. Refer to  REMOVAL [10/2022 - ] 

    Result: 

    OK 

    See step  4

  4. CHECK FUSE (PM-IGCT) 
    1. Remove the PM-IGCT fuse from the No. 1 luggage room relay block and No. 1 junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      PM-IGCT fuse Always Below 1 Ω

      Result

      Proceed to
      OK
      NG
    3. Install the PM-IGCT fuse.

    Result: 

    NG 

    See step  10

    Result: 

    OK 

    See step  5

  5. INSPECT RELAY (IGCT-SCENE) 
    1. Remove the IGCT SCENE relay from the No. 1 luggage room relay block and No. 1 junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.
      GTY434306Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 IGCT SCENE Relay

      Standard Resistance

      Tester Connection Condition Specified Condition
      3 - 5 Auxiliary battery voltage not applied between terminals 1 and 2 10 kΩ or higher
      Auxiliary battery voltage applied between terminals 1 and 2 Below 1 Ω

      Result

      Proceed to
      OK
      NG
    3. Install the IGCT SCENE relay.

    Result: 

    NG 

    REPLACE RELAY (IGCT SCENE) 

    Result: 

    OK 

    See step  6

  6. CHECK HARNESS AND CONNECTOR (NO. 1 LUGGAGE ROOM RELAY BLOCK AND NO. 1 JUNCTION BLOCK ASSEMBLY - HYBRID VEHICLE CONTROL ECU) 
    1. Disconnect the hybrid vehicle control ECU connectors.
    2. Remove the PM-IGCT fuse from the No. 1 luggage room relay block and No. 1 junction block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      C59-8 (+B1) - 2 (PM-IGCT fuse holder) Always Below 1 Ω
      A21-10 (+B2) - 2 (PM-IGCT fuse holder) Always Below 1 Ω
    4. Install the PM-IGCT fuse.
    5. Reconnect the hybrid vehicle control ECU connectors.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  7

  7. CHECK HARNESS AND CONNECTOR (NO. 1 LUGGAGE ROOM RELAY BLOCK AND NO. 1 JUNCTION BLOCK ASSEMBLY) 
    1. Remove the PM-IGCT fuse and IGCT SCENE relay from the No. 1 luggage room relay block and No. 1 junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      5 (IGCT SCENE relay holder) - 1 (PM-IGCT fuse holder) Always Below 1 Ω
    3. Install the PM-IGCT fuse and IGCT SCENE relay.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  8

  8. CHECK HARNESS AND CONNECTOR (HYBRID VEHICLE CONTROL ECU - NO. 1 LUGGAGE ROOM RELAY BLOCK AND NO. 1 JUNCTION BLOCK ASSEMBLY) 
    1. Disconnect the hybrid vehicle control ECU connector.
    2. Remove the IGCT SCENE relay from the No. 1 luggage room relay block and No. 1 junction block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      C59-10 (MREL) - 1 (IGCT SCENE relay holder) Always Below 1 Ω
      C59-10 (MREL) or 1 (IGCT SCENE relay holder) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG
    4. Install the IGCT SCENE relay.
    5. Reconnect the hybrid vehicle control ECU connector.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  9

  9. CHECK HARNESS AND CONNECTOR (NO. 1 LUGGAGE ROOM RELAY BLOCK AND NO. 1 JUNCTION BLOCK ASSEMBLY - BODY GROUND) 
    1. Remove the IGCT SCENE relay from the No. 1 luggage room relay block and No. 1 junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      2 (IGCT SCENE relay holder) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG
    3. Install the IGCT SCENE relay.

    Result: 

    OK 

    CHECK FOR INTERMITTENT PROBLEMS. Refer to  CHECK FOR INTERMITTENT PROBLEMS [08/2023 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  10. CHECK HARNESS OR CONNECTOR (NO. 1 LUGGAGE ROOM RELAY BLOCK AND NO. 1 JUNCTION BLOCK ASSEMBLY - HYBRID VEHICLE CONTROL ECU) 
    1. Remove the PM-IGCT fuse from the No. 1 luggage room relay block and No. 1 junction block assembly.
    2. Disconnect the hybrid vehicle control ECU connectors.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      C59-8 (+B1) or 2 (PM-IGCT fuse holder) - Body ground and other terminals Always 10 kΩ or higher
      A21-10 (+B2) or 2 (PM-IGCT fuse holder) - Body ground and other terminals Always 10 kΩ or higher
    4. Reconnect the hybrid vehicle control ECU connectors.
    5. Install the PM-IGCT fuse.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE FUSE (PM-IGCT) 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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