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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 P1644-00: ECU Malfunction (Starter Circuit) [10/2022 - 11/2023] >> Procedure

DTC P1644-00: ECU Malfunction (Starter Circuit) [10/2022 - 11/2023]: Procedure

  1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P1644-00) 
    1. Read the DTCs.

      Powertrain > Stop and Start > Trouble Codes 

      Result

      Result Proceed to
      DTC P1644-00 is output A
      DTCs P060B-1C, P060B-49 or P060B-71 and P1644-00 are output B
      DTCs P0615-11 and P1644-00 are output C

      HINT: 

      If DTCs P060B-1C, P060B-49, P060B-71 or P0615-11 and P1644-00 are output simultaneously, troubleshoot for DTC P060B-1C, P060B-49, P060B-71 or P0615-11 first.

    Result: 

    B 

    GO TO DTC P060B-1C, P060B-49 OR P060B-71. Refer to  DTC P060B-1C: Analog to Digital Converter Circuit Voltage Out of Range; DTC P060B-49: Analog to Digital Converter Internal Electronic Failure; DTC P060B-71: Analog to Digital Converter Actuator Stuck [10/2022 - 11/2023] 

    Result: 

    C 

    GO TO DTC P0615-11. Refer to  DTC P0615-11: Starter Relay Circuit Short to Ground [10/2022 - 11/2023] 

    Result: 

    A 

    See step  2

  2. CHECK HARNESS AND CONNECTOR (ENGINE STOP AND START ECU - ST RELAY) 
    1. Disconnect the engine stop and start ECU connector.
    2. Remove the ST relay from the No. 1 engine room relay block and No. 1 junction block assembly.
    3. Disconnect the certification ECU (smart key ECU assembly) connector.
    4. Disconnect the ECM connector.
    5. Disconnect the Park/Neutral Position Switch Assembly connector.
    6. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A34-21 (STA) - ST relay terminal 2 Always Below 1 Ω
      A34-21 (STA) - Body ground Always 10 kΩ or higher
      ST relay terminal 2 - Body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  3

  3. INSPECT RELAY (ST RELAY) 
    1. Inspect the ST relay.

      Refer to ON-VEHICLE INSPECTION [10/2022 - ]

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE RELAY (ST RELAY) 

    Result: 

    OK 

    See step  4

  4. CHECK HARNESS AND CONNECTOR (ST RELAY - BODY GROUND) 
    1. Remove the ST 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
      ST relay terminal 1 - Body ground Always Below 1 Ω

      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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