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DTC B1790: Center Airbag Sensor Assembly Communication Circuit Malfunction [10/2014 - 05/2019]: Procedure

  1. CHECK DTC 
    1. Turn the engine switch on (IG), and wait for at least 60 seconds.
    2. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Clear DTCs 

      HINT: 

      • First clear the DTCs stored in the occupant detection ECU, and then clear the DTCs stored in the airbag ECU assembly.
      • Use the Techstream to clear the DTCs of the occupant detection ECU, otherwise the DTCs cannot be cleared.
    3. Turn the engine switch off.
    4. Turn the engine switch on (IG), and wait for at least 60 seconds.
    5. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Trouble Codes 

      Result

      Proceed to
      DTC B1790 is not output
      DTC B1790 is output

      HINT: 

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

    Result: 

    DTC B1790 is not output 

    USE SIMULATION METHOD TO CHECK. Refer to  DIAGNOSIS SYSTEM [10/2014 - ] 

    Result: 

    DTC B1790 is output 

    See step  2

  2. CHECK CONNECTION OF CONNECTORS 
    1. Turn the engine switch off.
    2. Disconnect the cable from the negative (-) battery terminal, and wait for at least 90 seconds.
    3. Check that the connectors are properly connected to the occupant detection ECU and airbag ECU assembly.

      Result

      Proceed to
      Connectors are properly connected
      Connectors are not properly connected

    Result: 

    Connectors are not properly connected 

    CONNECT CONNECTOR 

    Result: 

    Connectors are properly connected 

    See step  3

  3. CHECK CONNECTORS 
    1. Disconnect the connectors from the airbag ECU assembly and occupant detection ECU.
      GTY378941Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU assembly
    2. Check that the connectors (on the airbag ECU assembly side and occupant detection ECU side) are not damaged.

      Result

      Proceed to
      Connectors are not deformed or damaged
      Connectors are deformed or damaged

    Result: 

    Connectors are deformed or damaged 

    REPLACE HARNESS AND CONNECTOR 

    Result: 

    Connectors are not deformed or damaged 

    See step  4

  4. CHECK AIRBAG ECU ASSEMBLY CIRCUIT 
    1. Connect the cable to the negative (-) battery terminal, and wait for at least 2 seconds.
      GTY496216Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *3 Connector E
      *4 Connector B
      *5 Service Wire
      *a Front view of wire harness connector
      (to Occupant Detection ECU)
      *b Rear view of wire harness connector
      (to Airbag ECU Assembly)
    2. Turn the engine switch on (IG).
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      f15-7 (FSR+) - Body ground Engine switch on (IG) Below 1 V
      f15-4 (FSR-) - Body ground
    4. Turn the engine switch off.
    5. Disconnect the cable from the negative (-) battery terminal, and wait for at least 90 seconds.
    6. Using a service wire, connect terminals 9 (FSR+) and 17 (FSR-) of connector B.
      NOTE:

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

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

      Standard Resistance

      Tester Connection Condition Specified Condition
      f15-7 (FSR+) - f15-4 (FSR-) Always Below 1 Ω
    8. Disconnect the service wire from connector B.
    9. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      f15-7 (FSR+) - f15-4 (FSR-) Always 1 MΩ or higher
      f15-7 (FSR+) - Body ground
      f15-4 (FSR-) - Body ground

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  10

    Result: 

    OK 

    See step  5

  5. CHECK DTC 
    1. Connect the connectors to the occupant detection ECU and airbag ECU assembly.
    2. Connect the cable to the negative (-) battery terminal, and wait for at least 2 seconds.
    3. Turn the engine switch on (IG), and wait for at least 60 seconds.
    4. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Clear DTCs 

      HINT: 

      • First clear the DTCs stored in the occupant detection ECU, and then clear the DTCs stored in the airbag ECU assembly.
      • Use the Techstream to clear the DTCs of the occupant detection ECU, otherwise the DTCs cannot be cleared.
    5. Turn the engine switch off.
    6. Turn the engine switch on (IG), and wait for at least 60 seconds.
    7. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Trouble Codes 

      Result

      Proceed to
      DTC B1790 is not output
      DTC B1790 is output

      HINT: 

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

    Result: 

    DTC B1790 is not output 

    USE SIMULATION METHOD TO CHECK. Refer to  DIAGNOSIS SYSTEM [10/2014 - ] 

    Result: 

    DTC B1790 is output 

    See step  6

  6. REPLACE OCCUPANT DETECTION ECU 
    1. Turn the engine switch off.
    2. Disconnect the cable from the negative (-) battery terminal, and wait for at least 90 seconds.
    3. Replace the occupant detection ECU.

      Refer to REMOVAL [10/2014 - 05/2019]

      HINT: 

      Perform the inspection using parts from a normal vehicle when possible.

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  7

  7. PERFORM ZERO POINT CALIBRATION 
    1. Connect the cable to the negative (-) battery terminal, and wait for at least 2 seconds.
    2. Turn the engine switch on (IG).
    3. Perform the zero point calibration.

      Refer to INITIALIZATION [10/2014 - ]

      Result

      Proceed to
      "Zero Point Calibration is complete." is displayed

    Result: 

    "Zero Point Calibration is complete." is displayed 

    See step  8

  8. PERFORM SENSITIVITY CHECK 
    1. Perform the sensitivity check.

      Refer to INITIALIZATION [10/2014 - ]

      Standard

      27 to 33 kg (59.5 to 72.8 lb)

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  9

  9. CHECK DTC 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Clear DTCs 

      HINT: 

      • First clear the DTCs stored in the occupant detection ECU, and then clear the DTCs stored in the airbag ECU assembly.
      • Use the Techstream to clear the DTCs of the occupant detection ECU, otherwise the DTCs cannot be cleared.
    2. Turn the engine switch off.
    3. Turn the engine switch on (IG), and wait for at least 60 seconds.
    4. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Trouble Codes 

      Result

      Proceed to
      DTC B1790 is not output
      DTC B1790 is output

      HINT: 

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

    Result: 

    DTC B1790 is not output 

    END (OCCUPANT DETECTION ECU WAS DEFECTIVE) 

    Result: 

    DTC B1790 is output 

    REPLACE AIRBAG ECU ASSEMBLY. Refer to  REMOVAL [10/2014 - 05/2019] 

  10. CHECK FRONT SEAT WIRE RH 
    1. Disconnect the front seat wire RH connector from the floor wire.
      GTY514252Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Front Seat Wire RH
      *2 Floor Wire
      *3 Occupant Detection ECU
      *4 Airbag ECU Assembly
      *5 Service Wire
      *6 Connector E
      *7 Connector D
      *a Front view of wire harness connector
      (to Occupant Detection ECU)
      *b Front view of wire harness connector
      (to Floor Wire)
    2. Connect the cable to the negative (-) battery terminal, and wait for at least 2 seconds.
    3. Turn the engine switch on (IG).
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      Pf2-7 (FSR+) - Body ground Engine switch on (IG) Below 1 V
      Pf2-3 (FSR-) - Body ground
    5. Turn the engine switch off.
    6. Disconnect the connector from the occupant detection ECU.
    7. Using a service wire, connect terminals 7 (FSR+) and 4 (FSR-) of connector E.
      NOTE:

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

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

      Standard Resistance

      Tester Connection Condition Specified Condition
      Pf2-7 (FSR+) - Pf2-3 (FSR-) Always Below 1 Ω
    9. Disconnect the service wire from connector E.
    10. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      Pf2-7 (FSR+) - Pf2-3 (FSR-) Always 1 MΩ or higher
      Pf2-7 (FSR+) - Body ground
      Pf2-3 (FSR-) - Body ground

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE FLOOR WIRE 

    Result: 

    NG 

    REPLACE FRONT SEAT WIRE RH 

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