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Home >> Lexus >> 2020 >> LS 500 Base, AWD >> Repair and Diagnosis >> Accessories & Equipment >> Gauges & Instrument Panels >> Meter / Gauge System - Diagnostic Codes (2 Of 2), Circuit & Symptom Tests >> Meter / Gauge System >> Speed Signal Circuit [12/2017 - 10/2022] >> Procedure

Speed Signal Circuit [12/2017 - 10/2022]: Procedure

  1. CHECK ECU TERMINAL VOLTAGE (INPUT VOLTAGE) 
    1. Disconnect the combination meter assembly connector.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      G34-19 (+S) - Body ground Engine switch on (IG) 4.5 to 14 V

      HINT: 

      If any of the ECUs specified in the wiring diagram supplies power to the combination meter assembly, the combination meter assembly will output a waveform.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  5

    Result: 

    OK 

    See step  2

  2. CHECK COMBINATION METER ASSEMBLY (OUTPUT VOLTAGE) 
    1. Reconnect the G34 combination meter assembly connector.
    2. Disconnect the A9*1, A11*2 skid control ECU connector.
      1. *1: w/ Vacuum Brake Booster
      2. *2: w/o Vacuum Brake Booster
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      W/ VACUUM BRAKE BOOSTER

      Tester Connection Switch Condition Specified Condition
      A9-14 (SP1) - Body ground Engine switch on (IG) 11 to 14 V
      W/O VACUUM BRAKE BOOSTER

      Tester Connection Switch Condition Specified Condition
      A11-22 (SP1) - Body ground Engine switch on (IG) 11 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  4

    Result: 

    OK 

    See step  3

  3. CHECK SKID CONTROL ECU (INPUT WAVEFORM) 
    1. Check the input waveform.
      GTY783522Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Combination Meter Assembly)
      1. Reconnect the A9*1, A11*2 skid control ECU connector.
        1. *1: w/ Vacuum Brake Booster
        2. *2: w/o Vacuum Brake Booster
      2. Remove the combination meter assembly with the connector(s) still connected.
      3. Connect an oscilloscope to terminal G34-20 (SI) and body ground.
      4. Turn the engine switch on (IG).
      5. Turn a wheel slowly.
      6. Check the signal waveform according to the condition(s) in the table below.
        Item Condition
        Tester Connection G34-20 (SI) - Body ground
        Tool setting 5 V/DIV., 20 ms./DIV.
        Vehicle condition Engine switch on (IG) wheel being rotated

        OK

        The waveform is similar to that shown in the illustration.

        HINT: 

        When the system is functioning normally, one wheel revolution generates 4 pulses. As the vehicle speed increases, the width indicated by (A) in the illustration narrows.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE COMBINATION METER ASSEMBLY. Refer to  REMOVAL [12/2017 - 10/2020]  , or refer to  REMOVAL [10/2020 - 10/2023] 

    Result: 

    NG 

    REPLACE SKID CONTROL ECU 

    w/ Vacuum Brake Booster: Refer to REMOVAL [12/2017 - 09/2018] , or refer to REMOVAL [09/2018 - 10/2020] , or refer to REMOVAL [10/2020 - 10/2022]

    w/o Vacuum Brake Booster: Refer to REMOVAL [12/2017 - 09/2018] , or refer to REMOVAL [09/2018 - 10/2020] , or refer to REMOVAL [10/2020 - 10/2022]

  4. CHECK HARNESS AND CONNECTOR (COMBINATION METER ASSEMBLY - SKID CONTROL ECU) 
    1. Disconnect the G34 combination meter assembly connector.
    2. Disconnect the A9*1, A11*2 skid control ECU connector.
      1. *1: w/ Vacuum Brake Booster
      2. *2: w/o Vacuum Brake Booster
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      W/ VACUUM BRAKE BOOSTER

      Tester Connection Condition Specified Condition
      G34-20 (SI) - A9-14 (SP1) Always Below 1 Ω
      G34-20 (SI) - Other terminals and body ground Always 10 kΩ or higher
      W/O VACUUM BRAKE BOOSTER

      Tester Connection Condition Specified Condition
      G34-20 (SI) - A11-22 (SP1) Always Below 1 Ω
      G34-20 (SI) - Other terminals and body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE COMBINATION METER ASSEMBLY. Refer to  REMOVAL [12/2017 - 10/2020]  , or refer to  REMOVAL [10/2020 - 10/2023] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  5. CHECK HARNESS AND CONNECTOR (COMBINATION METER ASSEMBLY - EACH ECU) 
    1. Disconnect the G71 certification ECU (smart key ECU assembly) connector.
    2. Disconnect the L52 stereo component amplifier assembly connector.
    3. Disconnect the A95 ECM connector.
    4. Disconnect the G55 navigation ECU connector.
    5. Disconnect the G52 radio receiver assembly connector.
    6. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      G34-19 (+S) - Other terminals and body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  6

  6. INSPECT ECM (SHORT CIRCUIT IN ECM) 
    1. Reconnect the G71 certification ECU (smart key ECU assembly) connector.
    2. Reconnect the L52 stereo component amplifier assembly connector.
    3. Reconnect the G55 navigation ECU connector.
    4. Reconnect the G52 radio receiver assembly connector.
    5. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      G34-19 (+S) - Body ground Engine switch on (IG) 4.5 to 14 V

      HINT: 

      If the result is as specified, there may be a short circuit in the ECM.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE ECM. Refer to  REMOVAL [12/2017 - 09/2018]  , or refer to  REMOVAL [09/2018 - 10/2020]  , or refer to  REMOVAL [10/2020 - 10/2022] 

    Result: 

    NG 

    See step  7

  7. CHECK RADIO RECEIVER ASSEMBLY (SHORT CIRCUIT IN RADIO RECEIVER) 
    1. Disconnect the G52 radio receiver assembly connector.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      G34-19 (+S) - Body ground Engine switch on (IG) 4.5 to 14 V

      HINT: 

      If the result is as specified, there may be a short circuit in the radio receiver assembly.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE RADIO RECEIVER ASSEMBLY. Refer to  REMOVAL [12/2017 - 10/2022] 

    Result: 

    NG 

    See step  8

  8. CHECK STEREO COMPONENT AMPLIFIER ASSEMBLY (SHORT CIRCUIT IN STEREO COMPONENT AMPLIFIER) 
    1. Disconnect the L52 stereo component amplifier assembly connector.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      G34-19 (+S) - Body ground Engine switch on (IG) 4.5 to 14 V

      HINT: 

      If the result is as specified, there may be a short circuit in the stereo component amplifier assembly.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE STEREO COMPONENT AMPLIFIER ASSEMBLY. Refer to  REMOVAL [12/2017 - 10/2022] 

    Result: 

    NG 

    See step  9

  9. CHECK NAVIGATION ECU (SHORT CIRCUIT IN NAVIGATION ECU) 
    1. Disconnect the G55 navigation ECU connector.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      G34-19 (+S) - Body ground Engine switch on (IG) 4.5 to 14 V

      HINT: 

      If the result is as specified, there may be a short circuit in the navigation ECU.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE NAVIGATION ECU. Refer to  REMOVAL [12/2017 - 10/2022] 

    Result: 

    NG 

    REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY). Refer to  REMOVAL [12/2017 - 09/2018]  , or refer to  REMOVAL [09/2018 - 10/2020]  , or refer to  REMOVAL [10/2020 - 10/2022] 

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