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ECU Power Source Circuit [11/2023 - ]: Procedure

WARNING: This page is about a different car, the 2025 Toyota Highlander and 2024 Toyota Highlander. However, it is still accessible from the selected car via links, so may be relevant.
  1. CHECK HYBRID VEHICLE CONTROL ECU (+B1, +B2 VOLTAGE) 
    1. Turn the ignition switch to ON.
    2. Measure the voltage according to the value(s) in the table below.
      GTY1180845Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Hybrid Vehicle Control ECU)      		 - -

      Standard Voltage

      Tester Connection Condition Specified Condition
      H67-7 (+B1) - Body ground Ignition switch ON 11 to 14 V
      H67-8 (+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 A32 and H67 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
      H67-15 (E1) - Body ground Always Below 1 Ω
      A32-10 (E01) - Body ground Always Below 1 Ω
      H67-1 (E12) - Body ground Always Below 1 Ω
    3. Reconnect the A32 and H67 hybrid vehicle control ECU connectors.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    GO TO PROBLEM SYMPTOMS TABLE. Refer to  PROBLEM SYMPTOMS TABLE [11/2023 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  3. CHECK HYBRID VEHICLE CONTROL ECU (MREL TERMINAL VOLTAGE) 
    1. Turn the ignition switch to ON.
    2. Measure the voltage according to the value(s) in the table below.
      GTY1181162Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Hybrid Vehicle Control ECU)      		 - -

      Standard Voltage

      Tester Connection Condition Specified Condition
      H67-47 (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. Refer to  REMOVAL [11/2023 - ] 

    Result: 

    OK 

    See step  4

  4. CHECK FUSE (IGCT NO. 1) 
    1. Remove the IGCT NO. 1 fuse from the No. 5 floor relay block and No. 5 floor junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      IGCT NO. 1 fuse Always Below 1 Ω
    3. Install the IGCT NO. 1 fuse.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  11

    Result: 

    OK 

    See step  5

  5. CHECK FUSE (IGCT-IG) 
    1. Remove the IGCT-IG fuse from the No. 5 floor relay block and No. 5 floor junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      IGCT-IG fuse Always Below 1 Ω
    3. Install the IGCT-IG fuse.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  12

    Result: 

    OK 

    See step  6

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

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE RELAY (IGCT) 

    Result: 

    OK 

    See step  7

  7. CHECK HARNESS AND CONNECTOR (IGCT NO. 1 FUSE - HYBRID VEHICLE CONTROL ECU) 
    1. Disconnect the H67 hybrid vehicle control ECU connector.
    2. Remove the IGCT NO. 1 fuse from the No. 5 floor relay block and No. 5 floor junction block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H67-7 (+B1) - 2 (IGCT NO. 1 fuse holder) Always Below 1 Ω
      H67-8 (+B2) - 2 (IGCT NO. 1 fuse holder) Always Below 1 Ω
    4. Reconnect the H67 hybrid vehicle control ECU connector.
    5. Install the IGCT NO. 1 fuse.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  8

  8. CHECK HARNESS AND CONNECTOR (NO. 5 FLOOR RELAY BLOCK AND NO. 5 FLOOR JUNCTION BLOCK ASSEMBLY) 
    1. Remove the IGCT-IG fuse, IGCT NO. 1 fuse and IGCT relay from the No. 5 floor relay block and No. 5 floor junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      3 (IGCT relay holder) - 2 (IGCT-IG fuse holder) Always Below 1 Ω
      5 (IGCT relay holder) - 1 (IGCT NO. 1 fuse holder) Always Below 1 Ω
    3. Install the IGCT-IG fuse, IGCT NO. 1 fuse and IGCT relay.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  9

  9. CHECK HARNESS AND CONNECTOR (IGCT RELAY - HYBRID VEHICLE CONTROL ECU) 
    1. Disconnect the H67 hybrid vehicle control ECU connector.
    2. Remove the IGCT relay from the No. 5 floor relay block and No. 5 floor junction block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H67-47 (MREL) - 1 (IGCT relay holder) Always Below 1 Ω
      H67-47 (MREL) or 1 (IGCT relay holder) - Body ground and other terminals Always 10 kΩ or higher
    4. Install the IGCT relay.
    5. Reconnect the H67 hybrid vehicle control ECU connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  10

  10. CHECK HARNESS AND CONNECTOR (IGCT RELAY - BODY GROUND) 
    1. Remove the IGCT relay from the No. 5 floor relay block and No. 5 floor 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 relay holder) - Body ground Always Below 1 Ω
    3. Install the IGCT relay.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    CHECK FOR INTERMITTENT PROBLEMS. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [12/2019 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  11. CHECK HARNESS AND CONNECTOR (IGCT NO. 1 FUSE - HYBRID VEHICLE CONTROL ECU) 
    1. Remove the IGCT NO. 1 fuse from the No. 5 floor relay block and No. 5 floor junction block assembly.
    2. Disconnect the H67 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
      H67-7 (+B1) or 2 (IGCT NO. 1 fuse holder) - Body ground and other terminals Always 10 kΩ or higher
      H67-8 (+B2) or 2 (IGCT NO. 1 fuse holder) - Body ground and other terminals Always 10 kΩ or higher
    4. Reconnect the H67 hybrid vehicle control ECU connectors.
    5. Install the IGCT NO. 1 fuse.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE FUSE (IGCT NO. 1) 

    Result: 

    NG 

    See step  13

  12. CHECK HARNESS AND CONNECTOR (NO. 5 FLOOR RELAY BLOCK AND NO. 5 FLOOR JUNCTION BLOCK ASSEMBLY) 
    1. Remove the IGCT-IG fuse, IGCT NO. 1 fuse and IGCT relay from the No. 5 floor relay block and No. 5 floor junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      3 (IGCT relay holder) or 2 (IGCT-IG fuse holder) - Body ground and other terminals Always 10 kΩ or higher
      5 (IGCT relay holder) or 1 (IGCT NO. 1 fuse holder) - Body ground and other terminals Always 10 kΩ or higher
    3. Install the IGCT-IG fuse, IGCT NO. 1 fuse and IGCT relay.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE FUSE (IGCT-IG) 

    Result: 

    NG 

    See step  14

  13. REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result

    Proceed to
    NEXT

    Result: 

    NEXT 

    REPLACE FUSE (IGCT NO. 1) 

  14. REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result

    Proceed to
    NEXT

    Result: 

    NEXT 

    REPLACE FUSE (IGCT-IG) 

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