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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 P177A-87: Lost Communication with Gear Shift Control Module Backup Power Supply Missing Message [08/2023 - ] >> Procedure

DTC P177A-87: Lost Communication with Gear Shift Control Module Backup Power Supply Missing Message [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 VEHICLE CONDITION 
    1. Choose the model to be inspected.

      Result

      Result Proceed to
      w/o Advanced Park (Remote Controlled) A
      w/ Advanced Park (Remote Controlled) B

    Result: 

    B 

    See step  7

    Result: 

    A 

    See step  2

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

    Pre-procedure1

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

      Standard Resistance

      Tester Connection Condition Specified Condition Result
      C35-17 (BUBI) - H116-3 (RO) Always Below 1 Ω Ω
      C35-17 (BUBI) or H116-3 (RO) - Body ground and other terminals Always 10 kΩ or higher kΩ

      Result

      Proceed to
      OK
      NG

    Post-procedure1

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

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  3

  3. INSPECT TRANSMISSION FLOOR SHIFT ASSEMBLY (SHIFT CONTROL ECU) (CHECK BUBI TERMINAL WAVEFORM) 

    Pre-procedure1

    • Connect an oscilloscope between the transmission floor shift assembly (shift control ECU) terminals specified in the table below.
      GTY1123112Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Transmission Floor Shift Assembly (Shift Control ECU))
      *b Waveform (Integrated capacitor condition signal)
    • Turn the ignition switch to ON and measure the waveform.
      Tester Connection Condition Equipment Setting
      C35-17 (BUBI) - C35-9 (E1) Ignition switch ON 10 V/DIV., 10 ms./DIV.

      HINT: 

      The duty ratio changes according to the vehicle condition.

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Turn the ignition switch off.

    Result: 

    OK 

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

    Result: 

    NG 

    See step  4

  4. INSPECT INTEGRATION CONTROL SUPPLY (INTEGRATED CAPACITOR) (+B TERMINAL VOLTAGE) 

    Pre-procedure1

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

      Standard Voltage

      Tester Connection Condition Specified Condition Result
      H116-7 (+B) - Body ground Always 11 to 14 V V

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  5

  5. INSPECT INTEGRATION CONTROL SUPPLY (INTEGRATED CAPACITOR) (IG 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 Result
      H116-16 (IG) - Body ground Ignition switch ON 11 to 14 V V

      Result

      Proceed to
      OK
      NG
      NOTE:

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

    Post-procedure1

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

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  6

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

    Pre-procedure1

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

      Standard Resistance

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

      Result

      Proceed to
      OK
      NG

    Post-procedure1

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

    Result: 

    OK 

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

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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

    Pre-procedure1

    • Disconnect the C35 transmission floor shift assembly (shift control ECU) connector.
    • Disconnect the H191 integration control supply (integrated capacitor) connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition Result
      C35-17 (BUBI) - H191-15 (RO) Always Below 1 Ω Ω
      C35-17 (BUBI) or H191-15 (RO) - Body ground and other terminals Always 10 kΩ or higher kΩ

      Result

      Proceed to
      OK
      NG

    Post-procedure1

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

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  8

  8. INSPECT TRANSMISSION FLOOR SHIFT ASSEMBLY (SHIFT CONTROL ECU) (CHECK BUBI TERMINAL WAVEFORM) 

    Pre-procedure1

    • Connect an oscilloscope between the transmission floor shift assembly (shift control ECU) terminals specified in the table below.
      GTY1123112Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Transmission Floor Shift Assembly (Shift Control ECU))
      *b Waveform (Integrated capacitor condition signal)
    • Turn the ignition switch to ON and measure the waveform.
      Tester Connection Condition Equipment Setting
      C35-17 (BUBI) - C35-9 (E1) Ignition switch ON 10 V/DIV., 10 ms./DIV.

      HINT: 

      The duty ratio changes according to the vehicle condition.

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Turn the ignition switch off.

    Result: 

    OK 

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

    Result: 

    NG 

    See step  9

  9. INSPECT INTEGRATION CONTROL SUPPLY (INTEGRATED CAPACITOR) (+B TERMINAL VOLTAGE) 

    Pre-procedure1

    • Disconnect the H191 integration control supply (integrated capacitor) connector.
    • Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition Result
      H191-7 (+B) - Body ground Always 11 to 14 V V

      Result

      Proceed to
      OK
      NG

    Post-procedure1

    • Connect the integration control supply (integrated capacitor) connector.

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  10

  10. INSPECT INTEGRATION CONTROL SUPPLY (INTEGRATED CAPACITOR) (IG TERMINAL VOLTAGE) 

    Pre-procedure1

    • Disconnect the H191 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 Result
      H191-16 (IG) - Body ground Ignition switch ON 11 to 14 V V

      Result

      Proceed to
      OK
      NG
      NOTE:

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

    Post-procedure1

    • Turn the ignition switch off.
    • 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 (SHIFT CONTROL ECU - INTEGRATED CAPACITOR) 

    Pre-procedure1

    • Disconnect the C35 transmission floor shift assembly (shift control ECU) connector.
    • Disconnect the H191 integration control supply (integrated capacitor) connector.
    • Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition Result
      C35-13 (BUB) - H191-6 (BUSE) Always Below 1 Ω Ω
      C35-13 (BUB) or H191-6 (BUSE) - Body ground and other terminals Always 10 kΩ or higher kΩ

      Result

      Proceed to
      OK
      NG

    Post-procedure1

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

    Result: 

    OK 

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

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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