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Home >> Toyota >> 2021 >> Highlander LE, 4WD >> Repair and Diagnosis >> Electrical >> Starter >> Stop And Start System - Diagnostic Codes (2 Of 3) >> Stop And Start System >> DTC P323A-00: Backup Boost Converter "A"; DTC P323A-16: Backup Boost Converter "A" Circuit Voltage Below Threshold; DTC P323B-14: Backup Boost Converter "A" Control Circuit Circuit Short to Ground or Open; DTC P323B-29: Backup Boost Converter "A" Control Circuit Signal Invalid; DTC P323B-38: Backup Boost Converter "A" Control Circuit Signal Cycle Invalid [10/2022 - 11/2023] >> Procedure

DTC P323A-00: Backup Boost Converter "A"; DTC P323A-16: Backup Boost Converter "A" Circuit Voltage Below Threshold; DTC P323B-14: Backup Boost Converter "A" Control Circuit Circuit Short to Ground or Open; DTC P323B-29: Backup Boost Converter "A" Control Circuit Signal Invalid; DTC P323B-38: Backup Boost Converter "A" Control Circuit Signal Cycle Invalid [10/2022 - 11/2023]: Procedure

  1. CHECK HARNESS AND CONNECTOR (ENGINE STOP AND START ECU - BBC NO. 1, BBC NO. 2 FUSES) 
    1. Disconnect the engine stop and start ECU connector.
    2. Remove the BBC NO. 1 and BBC NO. 2 fuses 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
      A33-1 (BIN2) - BBC NO. 2 fuse terminal 2 Always Below 1 Ω
      A33-3 (BIN1) - BBC NO. 1 fuse terminal 2 Always Below 1 Ω
      A33-1 (BIN2) - Body ground Always 10 kΩ or higher
      A33-3 (BIN1) - Body ground Always 10 kΩ or higher
      BBC NO. 2 fuse terminal 2 - Body ground Always 10 kΩ or higher
      BBC NO. 1 fuse terminal 2 - Body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (ENGINE STOP AND START ECU - BATTERY) 

    Result: 

    OK 

    See step  2

  2. CHECK HARNESS AND CONNECTOR (ENGINE STOP AND START ECU POWER SOURCE CIRCUIT) 
    1. Disconnect the engine stop and start ECU connectors.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A33-1 (BIN2) - Body ground Always 9.5 to 14 V
      A33-3 (BIN1) - Body ground Always 9.5 to 14 V
    3. Turn the ignition switch to ON.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      H66-18 (IGP) - Body ground Ignition switch ON 9.5 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (ENGINE STOP AND START ECU - BATTERY OR IGP NO. 1 RELAY) 

    Result: 

    OK 

    See step  3

  3. CHECK HARNESS AND CONNECTOR (ENGINE STOP AND START ECU - BODY GROUND) 
    1. Disconnect the engine stop and start ECU connector.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A33-2 (GND2) - Body ground Always Below 1 Ω
      A33-8 (GND1) - Body ground Always Below 1 Ω
      A34-6 (DGND) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  4

  4. CHECK HARNESS AND CONNECTOR (ENGINE STOP AND START ECU - EACH ECU OR SENSOR) 
    1. Disconnect the engine stop and start ECU connector.
    2. Disconnect the meter mirror sub-assembly connector.
    3. Disconnect the clearance warning ECU assembly connector.
    4. Disconnect the room light control relay connector.
    5. Disconnect the DOME CUT NO. 2 relay connector.
    6. Disconnect the tire pressure warning ECU and receiver connector.
    7. Disconnect the inner rear view mirror assembly LH connector.
    8. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H66-3 (IG41) - M43-5 (BLB)*1 Always Below 1 Ω
      H66-3 (IG41) - M2-5 (BRB)*1 Always Below 1 Ω
      H66-3 (IG41) - R1-1 (IG) Always Below 1 Ω
      H66-3 (IG41) - H59-11 (IG1) Always Below 1 Ω
      H66-3 (IG41) - H27-6 (IG+) Always Below 1 Ω
      H66-3 (IG41) - T2-9 (IG) Always Below 1 Ω
      H66-3 (IG41) - H46-1 (IG)*2 Always Below 1 Ω
      H66-3 (IG41) - H31-1 (IG)*3 Always Below 1 Ω
      H66-3 (IG41) - B6-8 (IGB) Always Below 1 Ω
      H66-3 (IG41) - H8-4 (IG+)*4 Always Below 1 Ω
      H66-2 (B41) - H31-2 (B)*3 Always Below 1 Ω
      H66-2 (B41) - M51-7 (+B) Always Below 1 Ω
      H66-2 (B41) - H8-1 (B)*4 Always Below 1 Ω
      H66-2 (B41) - 5 (DOME CUT NO. 2 relay) Always Below 1 Ω
      H66-12 (B42) - H107-4 (+B1) Always Below 1 Ω
      H66-11 (B43) - K5-2 (+) Always Below 1 Ω
      H66-11 (B43) - K10-2 (+)*5 Always Below 1 Ω
      H66-11 (B43) - J26-2 (+)*5 Always Below 1 Ω
      H66-11 (B43) - H68-2 (+)*5 Always Below 1 Ω
      H66-11 (B43) - H69-2 (+)*5 Always Below 1 Ω
      H66-3 (IG41) - Body ground Always 10 kΩ or higher
      H66-2 (B41) - Body ground Always 10 kΩ or higher
      H66-12 (B42) - Body ground Always 10 kΩ or higher
      H66-11 (B43) - Body ground Always 10 kΩ or higher

      *1: w/ Blind Spot Monitor System

      *2: w/ Parking Support Brake System

      *3: w/ Headup Display System

      *4: w/ 12.3 inch Display

      *5: w/ Ambient Illumination Light

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE ENGINE STOP AND START ECU. Refer to  REMOVAL [10/2022 - 11/2023] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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