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ECU Power Source Circuit [09/2023 - ]: Procedure

WARNING: This page is about a different car, the 2024 Lexus TX 500h. 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.
      GTY1231098Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Hybrid Vehicle Control ECU Assembly)      		 - -

      Standard Voltage

      Tester Connection Condition Specified Condition
      D44-8 (+B1) - Body ground Ignition switch ON 11 to 14 V
      B21-10 (+B2) - Body ground Ignition switch ON 11 to 14 V

      Result

      Proceed to
      OK
      NG
    3. Turn the ignition switch off.

    Result: 

    NG 

    See step  3

    Result: 

    OK 

    See step  2

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

      Standard Resistance

      Tester Connection Condition Specified Condition
      D44-1 (E1) - Body ground Always Below 1 Ω
      B21-12 (E01) - Body ground Always Below 1 Ω
      B21-24 (E12) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG
    3. Reconnect the hybrid vehicle control ECU assembly connectors.

    Result: 

    OK 

    GO TO PROBLEM SYMPTOMS TABLE. Refer to  PROBLEM SYMPTOMS TABLE [09/2023 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  3. CHECK HYBRID VEHICLE CONTROL ECU ASSEMBLY (MREL TERMINAL VOLTAGE) 
    1. Turn the ignition switch to ON.
    2. Measure the voltage according to the value(s) in the table below.
      GTY1234212Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Hybrid Vehicle Control ECU Assembly)      		 - -

      Standard Voltage

      Tester Connection Condition Specified Condition
      D44-10 (MREL) - Body ground Ignition switch ON 11 to 14 V

      Result

      Proceed to
      OK
      NG
    3. Turn the Ignition switch off.

    Result: 

    NG 

    REPLACE HYBRID VEHICLE CONTROL ECU ASSEMBLY. Refer to  REMOVAL [09/2023 - 12/2023]  , or refer to  REMOVAL [12/2023 - ] 

    Result: 

    OK 

    See step  4

  4. CHECK FUSE (PM-IGCT/ECU-IGP NO. 2) 
    1. Remove the PM-IGCT/ECU-IGP NO. 2 fuse from the No. 2 engine room relay block and No. 2 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/ECU-IGP NO. 2 fuse Always Below 1 Ω

      Result

      Proceed to
      OK
      NG
    3. Install the PM-IGCT/ECU-IGP NO. 2 fuse.

    Result: 

    NG 

    See step  10

    Result: 

    OK 

    See step  5

  5. CHECK RELAY (IGCT NO. 1) 

    Pre-procedure1

    1. Remove the IGCT NO. 1 relay from the No. 1 engine room relay block and No. 1 junction block assembly.

      Procedure1

    2. Measure the resistance according to the value(s) in the table below.
      GTY1196908Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 IGCT NO. 1 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

      Post-procedure1

    3. Install the IGCT NO. 1 relay.

    Result: 

    NG 

    REPLACE RELAY (IGCT NO. 1) 

    Result: 

    OK 

    See step  6

  6. CHECK HARNESS AND CONNECTOR (PM-IGCT/ECU-IGP NO. 2 FUSE - HYBRID VEHICLE CONTROL ECU ASSEMBLY) 
    1. Disconnect the hybrid vehicle control ECU assembly connector.
    2. Remove the PM-IGCT/ECU-IGP NO. 2 fuse from the No. 2 engine room relay block and No. 2 junction block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      D44-8 (+B1) - 2 (PM-IGCT/ECU-IGP NO. 2 fuse holder) Always Below 1 Ω
      B21-10 (+B2) - 2 (PM-IGCT/ECU-IGP NO. 2 fuse holder) Always Below 1 Ω

      Result

      Proceed to
      OK
      NG
    4. Reconnect the hybrid vehicle control ECU assembly connector.
    5. Install the PM-IGCT/ECU-IGP NO. 2 fuse.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  7

  7. CHECK HARNESS AND CONNECTOR (IGCT NO. 1 RELAY - PM-IGCT/ECU-IGP NO. 2 FUSE) 
    1. Remove the IGCT NO. 1 relay from the No. 1 engine room relay block and No. 1 junction block assembly.
    2. Remove the PM-IGCT/ECU-IGP NO. 2 fuse from the No. 2 engine room relay block and No. 2 junction block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      5 (IGCT NO. 1 relay holder) - 1 (PM-IGCT/ECU-IGP NO. 2 fuse holder) Always Below 1 Ω
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      3 (IGCT NO. 1 relay holder) - Body ground Always 7.5 to 14 V

      Result

      Proceed to
      OK
      NG
    5. Install the PM-IGCT/ECU-IGP NO. 2 fuse and IGCT NO. 1 relay.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  8

  8. CHECK HARNESS AND CONNECTOR (IGCT NO. 1 RELAY - HYBRID VEHICLE CONTROL ECU ASSEMBLY) 
    1. Disconnect the hybrid vehicle control ECU assembly connector.
    2. Remove the IGCT NO. 1 relay from the No. 1 engine 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
      D44-10 (MREL) - 1 (IGCT NO. 1 relay holder) Always Below 1 Ω
      D44-10 (MREL) or 1 (IGCT NO. 1 relay holder) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG
    4. Install the IGCT NO. 1 relay.
    5. Reconnect the hybrid vehicle control ECU assembly connector.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  9

  9. CHECK HARNESS AND CONNECTOR (IGCT NO. 1 RELAY - BODY GROUND) 
    1. Remove the IGCT NO. 1 relay from the No. 1 engine 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 NO. 1 relay holder) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG
    3. Install the IGCT NO. 1 relay.

    Result: 

    OK 

    CHECK FOR INTERMITTENT PROBLEMS. Refer to  ELECTRONIC CIRCUIT INSPECTION PROCEDURE [09/2023 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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

      Standard Resistance

      Tester Connection Condition Specified Condition
      D44-8 (+B1) or 2 (PM-IGCT/ECU-IGP NO. 2 fuse holder) - Body ground and other terminals Always 10 kΩ or higher
      B21-10 (+B2) or 2 (PM-IGCT/ECU-IGP NO. 2 fuse holder) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG
    4. Reconnect the hybrid vehicle control ECU assembly connectors.
    5. Install the PM-IGCT/ECU-IGP NO. 2 fuse.

    Result: 

    OK 

    REPLACE FUSE (PM-IGCT/ECU-IGP NO. 2) 

    Result: 

    NG 

    See step  11

  11. REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result

    Proceed to
    NEXT

    Result: 

    NEXT 

    REPLACE FUSE (PM-IGCT/ECU-IGP NO. 2) 

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