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Home >> Lexus >> 2024 >> RX 500h >> Repair and Diagnosis >> External Pages >> Different car >> Section 122 (Electronic A/T Shift Lever System - Diagnostic Codes (1 Of 2)) >> Electronic Shift Lever System >> DTC P1779-96: Gear Shift Control Module Backup Power Supply Component Internal Failure [10/2022 - 08/2023] >> Procedure

DTC P1779-96: Gear Shift Control Module Backup Power Supply Component Internal Failure [10/2022 - 08/2023]: Procedure

WARNING: This page is about a different car, the 2025 Lexus RX 350, 2024 Lexus RX 350, and 2023 Lexus RX 350. However, it is still accessible from the selected car via links, so may be relevant.
  1. CHECK DTC OUTPUT (TRANSMISSION) 

    Pre-procedure1

    • Turn the ignition switch to ON.
    • Check if DTCs are output.

      Powertrain > Transmission > Trouble Codes 

      Result

      Result Proceed to
      All DTCs in the below table are simultaneously output A
      A DTC in the below table is not simultaneously output B
      Relevant DTC
      P1779-96 Gear Shift Control Module Backup Power Supply Component Internal Failure
      P179D-49 Gear Shift Actuator "B" Control Circuit Internal Electronic Failure
      U0291-00 Lost Communication with Gear Shift Control Module "B" (System 2) Missing Message
      U1176-87 Lost Communication with Gear Shift Control Module "A" (ch2) Missing Message

      HINT: 

      • As the internal relay of the shift actuator ECU may be malfunctioning when all of the above DTCs are stored simultaneously, perform step 1 to determine the malfunctioning component.
      • Depending on the vehicle conditions, DTC P179D-49 may not be stored. Proceed to procedure A if DTCs other than this DTC P179D-49 are stored simultaneously.

    Post-procedure1

    • Turn the ignition switch off.

    Result: 

    B 

    See step  4

    Result: 

    A 

    See step  2

  2. CLEAR DTC 

    Pre-procedure1

    • Turn the ignition switch off and wait for 10 minutes or more.
    • Clear the DTCs.

      Powertrain > Transmission > Clear DTCs 

      Result

      Proceed to
      NEXT

    Post-procedure1

    • None

    Result: 

    NEXT 

    See step  3

  3. CHECK DTC OUTPUT (P1779-96) 

    Pre-procedure1

    • Disconnect the B56 shift control actuator assembly (shift actuator ECU) connector.
    • Turn the ignition switch to ON and wait for 10 seconds or more.
    • Turn the ignition switch off and wait for 10 minutes or more.
    • Turn the ignition switch to ON.
    • Check for DTCs.

      Powertrain > Transmission > Trouble Codes 

      Result

      Result Proceed to
      P1779-96 is output A
      P1779-96 is not output B
      NOTE:

      Turning the ignition switch to ON with the connector disconnected causes other DTCs to be stored. Clear the DTCs after performing this inspection.

      HINT: 

      Check for DTCs with the shift control actuator assembly (shift actuator ECU) side connector disconnected to judge whether the internal relay of the shift control actuator assembly (shift actuator ECU) is malfunctioning. If the shift control actuator assembly (shift actuator ECU) is malfunctioning, DTC P1779-96 is not stored.

    Post-procedure1

    • Turn the ignition switch off.
    • Connect the shift control actuator assembly (shift actuator ECU) connector.

    Result: 

    B 

    REPLACE SHIFT CONTROL ACTUATOR ASSEMBLY (SHIFT ACTUATOR ECU). Refer to  REMOVAL [10/2022 - ] 

    Result: 

    A 

    See step  4

  4. CHECK FREEZE FRAME DATA (GEAR SHIFT CONTROL MODULE BACKUP SIGNAL STATUS) 

    Pre-procedure1

    • Turn the ignition switch to ON.
    • 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

    Post-procedure1

    • Turn the ignition switch off.

    Result: 

    B 

    See step  14

    Result: 

    A 

    See step  5

  5. CHECK FREEZE FRAME DATA (GEAR SHIFT CONTROL MODULE BACKUP SIGNAL STATUS) 

    Pre-procedure1

    • Turn the ignition switch to ON.
    • 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 (Backup Possible) A
      The value of Gear Shift Control Module Backup Signal Status is Capacitor External Failure (Backup Possible) B

    Post-procedure1

    • Turn the ignition switch off.

    Result: 

    B 

    See step  8

    Result: 

    A 

    See step  6

  6. CLEAR DTC 

    Pre-procedure1

    • Turn the ignition switch off and wait for 10 minutes or more.
    • Clear the DTCs.

      Powertrain > Transmission > Clear DTCs 

      Result

      Proceed to
      NEXT

    Post-procedure1

    • None

    Result: 

    NEXT 

    See step  7

  7. CHECK DTC OUTPUT 

    Pre-procedure1

    • Turn the ignition switch to ON and wait for 10 seconds or more.
    • Turn the ignition switch off and wait for 5 minutes or more.
    • Check for DTCs.

      Powertrain > Transmission > Trouble Codes 

      Result

      Result Proceed to
      P1779-96 is output A
      P1779-96 is not output B

    Post-procedure1

    • Turn the ignition switch off.

    Result: 

    A 

    REPLACE INTEGRATION CONTROL SUPPLY (INTEGRATED CAPACITOR). Refer to  REMOVAL [10/2022 - 08/2023] 

    Result: 

    B 

    CHECK FOR INTERMITTENT PROBLEMS. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [10/2022 - ] 

  8. CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - POWER DESTRIBUTION BOX ASSEMBLY) 

    Pre-procedure1

    • Disconnect the H116 integration control supply (integrated capacitor) connector.
    • Disconnect the C90 power distribution box assembly connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H116-10 (BUE2) - C90-27 Always Below 1 Ω
      H116-10 (BUE2) or C90-27 - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the power distribution box assembly connector.
    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  9

  9. INSPECT POWER DISTRIBUTION BOX ASSEMBLY 

    Pre-procedure1

    • Remove the main body ECU (multiplex network body ECU) from the power distribution box assembly.

      HINT: 

      Refer to REMOVAL [10/2022 - 08/2023]

    • Measure the resistance according to the value(s) in the table below.
      GTY1128813Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component without harness connected
      (Power Distribution Box Assembly)      		 - -

      Standard Resistance

      Tester Connection Condition Specified Condition
      C90-27 or z31-25 (SBAT) - Other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Install the main body ECU (multiplex network body ECU) to the power distribution box assembly.

      HINT: 

      Refer to INSTALLATION [10/2022 - ]

    Result: 

    NG 

    REPLACE POWER DISTRIBUTION BOX ASSEMBLY. Refer to  REMOVAL [10/2022 - 08/2023] 

    Result: 

    OK 

    See step  10

  10. CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - FRONT DOOR LOCK WITH MOTOR ASSEMBLY LH) 

    Pre-procedure1

    • Disconnect the H116 integration control supply (integrated capacitor) connector.
    • Disconnect the D34 front door lock with motor assembly LH connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H116-20 (BUA2) - D34-3 (BUB1) Always Below 1 Ω
      H116-20 (BUA2) or D34-3 (BUB1) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the front door lock with motor assembly LH connector.
    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  11

  11. CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - FRONT DOOR LOCK WITH MOTOR ASSEMBLY RH) 

    Pre-procedure1

    • Disconnect the H116 integration control supply (integrated capacitor) connector.
    • Disconnect the D15 front door lock with motor assembly RH connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H116-20 (BUA2) - D15-3 (BUB2) Always Below 1 Ω
      H116-20 (BUA2) or D15-3 (BUB2) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the front door lock with motor assembly RH connector.
    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  12

  12. CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - REAR DOOR LOCK WITH MOTOR ASSEMBLY LH) 

    Pre-procedure1

    • Disconnect the H116 integration control supply (integrated capacitor) connector.
    • Disconnect the E16 rear door lock with motor assembly LH connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H116-20 (BUA2) - E16-3 (BUB4) Always Below 1 Ω
      H116-20 (BUA2) or E16-3 (BUB4) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the rear door lock with motor assembly LH connector.
    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  13

  13. CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - REAR DOOR LOCK WITH MOTOR ASSEMBLY RH) 

    Pre-procedure1

    • Disconnect the H116 integration control supply (integrated capacitor) connector.
    • Disconnect the E6 rear door lock with motor assembly RH connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H116-20 (BUA2) - E6-3 (BUB3) Always Below 1 Ω
      H116-20 (BUA2) or E6-3 (BUB3) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the rear door lock with motor assembly RH connector.
    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    OK 

    REPLACE INTEGRATION CONTROL SUPPLY (INTEGRATED CAPACITOR). Refer to  REMOVAL [10/2022 - 08/2023] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  14. CHECK HARNESS AND CONNECTOR (BR TERMINAL VOLTAGE) 

    Pre-procedure1

    • Disconnect the H116 integration control supply (integrated capacitor) connector.
    • Turn the ignition switch to ON.
    • Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      H116-14 (BR) - Body ground Ignition switch ON 8 to 14 V

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Turn the ignition switch off.
    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    NG 

    See step  17

    Result: 

    OK 

    See step  15

  15. CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - SHIFT CONTROL ECU) 

    Pre-procedure1

    • Disconnect the H116 integration control supply (integrated capacitor) connector.
    • Disconnect the C35 transmission floor shift assembly (shift control ECU) connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H116-1 (BUSE) - C35-13 (BUB) Always Below 1 Ω
      H116-1 (BUSE) or C35-13 (BUB) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the transmission floor shift assembly (shift control ECU) connector.
    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  16

  16. CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - SHIFT ACTUATOR ECU) 

    Pre-procedure1

    • Disconnect the H116 integration control supply (integrated capacitor) connector.
    • Disconnect the B56 shift control actuator assembly (shift actuator ECU) connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H116-19 (BUA) - B56-6 (MA2) Always Below 1 Ω
      H116-9 (BUAE) - B56-8 (BUB1) Always Below 1 Ω
      H116-19 (BUA) or B56-6 (MA2) - Body ground and other terminals Always 10 kΩ or higher
      H116-9 (BUAE) or B56-8 (BUB1) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the shift control actuator assembly (shift actuator ECU) connector.
    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    OK 

    REPLACE INTEGRATION CONTROL SUPPLY (INTEGRATED CAPACITOR). Refer to  REMOVAL [10/2022 - 08/2023] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  17. CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - SHIFT CONTROL ECU) 

    Pre-procedure1

    • Disconnect the H116 integration control supply (integrated capacitor) connector.
    • Disconnect the C35 transmission floor shift assembly (shift control ECU) connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H116-14 (BR) - C35-20 (BUBO) Always Below 1 Ω
      H116-14 (BR) or C35-20 (BUBO) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the transmission floor shift assembly (shift control ECU) connector.
    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    OK 

    REPLACE TRANSMISSION FLOOR SHIFT ASSEMBLY (SHIFT CONTROL ECU). Refer to  REMOVAL [10/2022 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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