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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 Internal Error [12/2019 - 10/2022] >> Procedure

DTC P1644-00: ECU Internal Error [12/2019 - 10/2022]: 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 P0615-19 and P1644-00 are output C

      HINT: 

      If DTCs P060B-1C, P060B-49, P060B-71 or P0615-19 and P1644-00 are output simultaneously, troubleshoot for DTC P060B-1C, P060B-49, P060B-71 or P0615-19 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 [12/2019 - 10/2022] 

    Result: 

    C 

    GO TO DTC P0615-19. Refer to  DTC P0615-19: Starter Relay Circuit Current Above Threshold [12/2019 - 10/2022] 

    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 park/neutral position switch assembly connector.
    5. Disconnect the ECM connector.
    6. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

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

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  3

  3. CHECK HARNESS AND CONNECTOR (ENGINE STOP AND START ECU - PARK/NEUTRAL POSITION SWITCH ASSEMBLY) 
    1. Disconnect the engine stop and start ECU connector.
    2. Disconnect the park/neutral position switch assembly connector.
    3. Disconnect the certification ECU (smart key ECU assembly) connector.
    4. Remove the ST relay from the No. 1 engine room relay block and No. 1 junction block assembly.
    5. Disconnect the ECM connector.
    6. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A34-21 (STA) - C52-9 (L) Always Below 1 Ω
      A34-21 (STA) or C52-9 (L) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  4

  4. INSPECT RELAY (ST RELAY) 

    Refer to PROCEDURE - Step 1

    Result

    Proceed to
    OK
    NG

    Result: 

    NG 

    REPLACE RELAY (ST RELAY) 

    Result: 

    OK 

    See step  5

  5. 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
      1 (ST relay) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE ENGINE STOP AND START ECU. Refer to  REMOVAL [12/2019 - 10/2022] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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