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DTC B1790: Center Airbag Sensor Assembly Communication Circuit Malfunction [06/2017 - ]: Procedure

  1. CHECK CONNECTORS 
    1. Turn the ignition switch off.
    2. Disconnect the cable from the negative (-) auxiliary battery terminal.
      WARNING:

      Wait at least 90 seconds after disconnecting the cable from the negative (-) auxiliary battery terminal to disable the SRS system.

    3. Check that the connectors are properly connected to the airbag sensor assembly and occupant detection ECU. Also check that the connectors that link the front seat wire RH and floor wire are properly connected.

      OK

      The connectors are properly connected.

      HINT: 

      If the connectors are not properly connected, reconnect the connectors and proceed to the next inspection.

    4. Disconnect the connectors from the airbag sensor assembly and occupant detection ECU. Also disconnect the connectors that link the front seat wire RH and floor wire.
    5. Check that the terminals of the connectors are not deformed or damaged.

      OK

      The terminals are not deformed or damaged.

    Result: 

    NG 

    REPLACE WIRE HARNESS 

    Result: 

    OK 

    See step  2

  2. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT TO B+) 
    1. Connect the connectors that link the floor wire and front seat wire RH.
      GTY762731Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *a Front view of wire harness connector
      (to Occupant Detection ECU)
    2. Connect the cable to the negative (-) auxiliary battery terminal.
    3. Turn the ignition switch to ON (IG).
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      Y3-7 (FSR+) - Body ground Ignition switch ON (IG) Below 1 V
      Y3-4 (FSR-) - Body ground Ignition switch ON (IG) Below 1 V
    5. Turn the ignition switch off.
    6. Disconnect the cable from the negative (-) auxiliary battery terminal.
      WARNING:

      Wait at least 90 seconds after disconnecting the cable from the negative (-) auxiliary battery terminal to disable the SRS system.

    Result: 

    NG 

    See step  10

    Result: 

    OK 

    See step  3

  3. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (OPEN) 
    1. Using a service wire, connect terminals 16 (FSR+) and 24 (FSR-) of connector B.
      GTY774602Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Service Wire
      *a Front view of wire harness connector
      (to Airbag Sensor Assembly)
      *b Front view of wire harness connector
      (to Occupant Detection ECU)
      NOTE:

      Do not forcibly insert the service wire into the terminals of the connector when connecting the wire.

    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      Y3-7 (FSR+) - Y3-4 (FSR-) Always Below 1 Ω

    Result: 

    NG 

    See step  11

    Result: 

    OK 

    See step  4

  4. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT) 
    1. Disconnect the service wire from connector B.
      GTY762731Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *a Front view of wire harness connector
      (to Occupant Detection ECU)
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      Y3-7 (FSR+) - Y3-4 (FSR-) Always 1 MΩ or higher

    Result: 

    NG 

    See step  12

    Result: 

    OK 

    See step  5

  5. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT TO GROUND) 
    1. Measure the resistance according to the value(s) in the table below.
      GTY762731Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *a Front view of wire harness connector
      (to Occupant Detection ECU)

      Standard Resistance

      Tester Connection Condition Specified Condition
      Y3-7 (FSR+) - Body ground Always 1 MΩ or higher
      Y3-4 (FSR-) - Body ground Always 1 MΩ or higher

    Result: 

    NG 

    See step  13

    Result: 

    OK 

    See step  6

  6. CHECK DTC 
    1. Connect the connectors to the occupant detection ECU and airbag sensor assembly.
    2. Connect the cable to the negative (-) auxiliary battery terminal.
    3. Clear the DTCs stored in the occupant detection ECU (Refer to DTC CHECK / CLEAR [11/2015 - ] ).
    4. Clear the DTCs stored in the airbag sensor assembly (Refer to DTC CHECK / CLEAR [11/2015 - ] ).
    5. Turn the ignition switch off.
    6. Turn the ignition switch to ON (IG).
    7. Check for DTCs (Refer to DTC CHECK / CLEAR [11/2015 - ] ).

      OK

      DTC B1790 is not output.

      HINT: 

      Codes other than DTC B1790 may be output at this time, but they are not related to this check.

    8. Turn the ignition switch off.

    Result: 

    OK 

    USE SIMULATION METHOD TO CHECK 

    (Refer to HOW TO PROCEED WITH TROUBLESHOOTING [11/2015 - ] )

    Result: 

    NG 

    See step  7

  7. CHECK OCCUPANT DETECTION ECU 
    1. Disconnect the cable from the negative (-) auxiliary battery terminal.
    2. Replace the occupant detection ECU with a known good one (Refer to REMOVAL [11/2015 - ] ).

      HINT: 

      Perform the following inspection using known good parts from another vehicle if possible.

    3. Connect the cable to the negative (-) auxiliary battery terminal.
    4. Clear the DTCs stored in the occupant detection ECU (Refer to DTC CHECK / CLEAR [11/2015 - ] ).
    5. Clear the DTCs stored in the airbag sensor assembly (Refer to DTC CHECK / CLEAR [11/2015 - ] ).
    6. Turn the ignition switch off.
    7. Turn the ignition switch to ON (IG).
    8. Check for DTCs (Refer to DTC CHECK / CLEAR [11/2015 - ] ).

      OK

      DTC B1790 is not output.

      HINT: 

      Codes other than DTC B1790 may be output at this time, but they are not related to this check.

    9. Turn the ignition switch off.
    10. Disconnect the cable from the negative (-) auxiliary battery terminal.
    11. Return the occupant detection ECU that was installed for testing to its original location (Refer to REMOVAL [11/2015 - ] ).

    Result: 

    NG 

    REPLACE AIRBAG SENSOR ASSEMBLY 

    (Refer to REMOVAL [11/2015 - ] )

    Result: 

    OK 

    See step  8

  8. REPLACE OCCUPANT DETECTION ECU 
    1. Disconnect the cable from the negative (-) auxiliary battery terminal.
    2. Replace the occupant detection ECU with a new one (Refer to REMOVAL [11/2015 - ] ).
    3. Connect the cable to the negative (-) auxiliary battery terminal.

    NEXT 

    See step  9

  9. PERFORM ZERO POINT CALIBRATION AND SENSITIVITY CHECK 
    1. Using the Techstream, perform Zero Point Calibration and Sensitivity Check (Refer to INITIALIZATION [06/2017 - ] ).

    NEXT 

    END 

  10. CHECK FLOOR WIRE (SHORT TO B+) 
    1. Disconnect the front seat wire RH connector from the floor wire.
      GTY765857Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Front Seat Wire RH
      *4 Floor Wire
      *a Front view of wire harness connector
      (to Front Seat Wire RH)
    2. Connect the cable to the negative (-) auxiliary battery terminal.
    3. Turn the ignition switch to ON (IG).
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      MY1-1 (FSR+) - Body ground Ignition switch ON (IG) Below 1 V
      MY1-5 (FSR-) - Body ground Ignition switch ON (IG) Below 1 V

    Result: 

    OK 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    NG 

    REPLACE FLOOR WIRE 

  11. CHECK FLOOR WIRE (OPEN) 
    1. Disconnect the front seat wire RH connector from the floor wire.
      GTY743144Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Front Seat Wire RH
      *4 Floor Wire
      *5 Service Wire
      *a Front view of wire harness connector
      (to Airbag Sensor Assembly)
      *b Front view of wire harness connector
      (to Front Seat Wire RH)

      HINT: 

      The service wire has already been inserted into connector B.

    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      MY1-1 (FSR+) - MY1-5 (FSR-) Always Below 1 Ω
    3. Disconnect the service wire from connector B.

    Result: 

    OK 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    NG 

    REPLACE FLOOR WIRE 

  12. CHECK FLOOR WIRE (SHORT) 
    1. Disconnect the front seat wire RH connector from the floor wire.
      GTY765857Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Front Seat Wire RH
      *4 Floor Wire
      *a Front view of wire harness connector
      (to Front Seat Wire RH)
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      MY1-1 (FSR+) - MY1-5 (FSR-) Always 1 MΩ or higher

    Result: 

    OK 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    NG 

    REPLACE FLOOR WIRE 

  13. CHECK FLOOR WIRE (SHORT TO GROUND) 
    1. Disconnect the front seat wire RH connector from the floor wire.
      GTY765857Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Front Seat Wire RH
      *4 Floor Wire
      *a Front view of wire harness connector
      (to Front Seat Wire RH)
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      MY1-1 (FSR+) - Body ground Always 1 MΩ or higher
      MY1-5 (FSR-) - Body ground Always 1 MΩ or higher

    Result: 

    OK 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    NG 

    REPLACE FLOOR WIRE 

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