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Home >> Lexus >> 2019 >> LS 500 Base, AWD >> Repair and Diagnosis (Single Page) >> Transmission >> Transmission Control Systems >> Electronic A/T Shift Lever System (Aga0F) - Diagnostic Codes (2 Of 5) >> Electronic Shift Lever System >> DTC P1779-96: Gear Shift Control Module Backup Power Supply Component Internal Failure [10/2023 - ] >> Procedure

DTC P1779-96: Gear Shift Control Module Backup Power Supply Component Internal Failure [10/2023 - ]: Procedure

  1. CHECK FREEZE FRAME DATA (GEAR SHIFT CONTROL MODULE BACKUP SIGNAL STATUS) 
    1. Read the freeze frame data of DTC P1779-96.

      Powertrain > Transmission > DTC(P1779-96) > Freeze Frame Data 

      Tester Display
      Gear Shift Control Module Backup Signal Status

      Result

      Result Proceed to
      The value of Gear Shift Control Module Backup Signal Status is not Capacitor External Failure A
      The value of Gear Shift Control Module Backup Signal Status is Capacitor External Failure B

    Result: 

    B 

    See step  4

    Result: 

    A 

    See step  2

  2. CLEAR DTC 
    1. Turn the engine switch off and wait for 10 minutes or more.
    2. Turn the engine switch on (IG).
    3. Clear the DTCs.

      Powertrain > Transmission > Clear DTCs 

      Result

      Proceed to
      NEXT
    4. Turn the engine switch off.

    Result: 

    NEXT 

    See step  3

  3. CHECK DTC OUTPUT (PERFORM A REPRODUCTION TEST) 
    1. Turn the engine switch on (IG) and wait for 10 seconds or more.
    2. Turn the engine switch off and wait for 10 minutes or more.
    3. Turn the engine switch on (IG).
    4. Check for DTCs.

      Powertrain > Transmission > Trouble Codes 

      Result

      Result Proceed to
      P1779-96 is output A
      P1779-96 is not output B
    5. Turn the engine switch off.

    Result: 

    A 

    REPLACE INTEGRATION CONTROL SUPPLY. Refer to  REMOVAL [10/2023 - ] 

    Result: 

    B 

    CHECK FOR INTERMITTENT PROBLEMS 

    Refer to HOW TO PROCEED WITH TROUBLESHOOTING [10/2023 - ]

    Refer to ELECTRONIC CIRCUIT INSPECTION PROCEDURE [12/2017 - ]

  4. CHECK HARNESS AND CONNECTOR (BR TERMINAL INPUT VOLTAGE) 
    1. Disconnect the L291 integration control supply connector.
    2. Turn the engine switch on (IG).
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      L291-14 (BR) - Body ground Engine switch on (IG) 8 to 14 V
    4. Turn the engine switch off.
    5. Reconnect the L291 integration control supply connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  7

    Result: 

    OK 

    See step  5

  5. CHECK HARNESS AND CONNECTOR (INTEGRATION CONTROL SUPPLY - SHIFT CONTROL ECU) 
    1. Disconnect the L291 integration control supply connector.
    2. Disconnect the G81 shift control ECU connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)

      Tester Connection Condition Specified Condition
      L291-1 (BUSE) - G81-10 (BUB) Always Below 1 Ω

      Standard Resistance (Check for Short)

      Tester Connection Condition Specified Condition
      L291-1 (BUSE) or G81-10 (BUB) - Body ground and other terminals Always 10 kΩ or higher
    4. Reconnect the G81 shift control ECU connector.
    5. Reconnect the L291 integration control supply connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  6

  6. CHECK HARNESS AND CONNECTOR (INTEGRATION CONTROL SUPPLY - NO. 2 LUGGAGE ROOM RELAY BLOCK) 
    1. Disconnect the L291 integration control supply connector.
    2. Remove the P CON MTR2 relay from the No. 2 luggage room relay block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)

      Tester Connection Condition Specified Condition
      L291-19 (BUA) - P CON MTR2 relay terminal 3 or 2 Always Below 1 Ω

      Standard Resistance (Check for Short)

      Tester Connection Condition Specified Condition
      L291-19 (BUA) or P CON MTR2 relay terminal 3 or 2 - Body ground and other terminals Always 10 kΩ or higher
    4. Install the P CON MTR2 relay.
    5. Rreconnect the L291 integration control supply connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE INTEGRATION CONTROL SUPPLY. Refer to  REMOVAL [10/2023 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  7. CHECK HARNESS AND CONNECTOR (INTEGRATION CONTROL SUPPLY - SHIFT CONTROL ECU) 
    1. Disconnect the L291 integration control supply connector.
    2. Disconnect the G81 shift control ECU connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)

      Tester Connection Condition Specified Condition
      L291-14 (BR) - G81-29 (BUBO) Always Below 1 Ω

      Standard Resistance (Check for Short)

      Tester Connection Condition Specified Condition
      L291-14 (BR) or G81-29 (BUBO) - Body ground and other terminals Always 10 kΩ or higher
    4. Reconnect the G81 shift control ECU connector.
    5. Reconnect the L291 integration control supply connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE SHIFT CONTROL ECU. Refer to  REMOVAL [10/2023 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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