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Home >> Lexus >> 2023 >> RC F Base >> Repair and Diagnosis (Single Page) >> Restraints >> Air Bag, SRS >> Occupant Classification System - Diagnostic Codes & Symptom Tests >> Occupant Classification System >> DTC B1790: Center Airbag Sensor Assembly Communication Circuit Malfunction [09/2014 - 03/2019] >> Procedure

DTC B1790: Center Airbag Sensor Assembly Communication Circuit Malfunction [09/2014 - 03/2019]: Procedure

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

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

    3. Check that the connectors are properly connected to the airbag ECU 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 ECU 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

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE WIRE HARNESS 

    Result: 

    OK 

    See step  2

  2. CHECK WIRE HARNESS (SHORT TO B+) 
    1. Connect the connectors that link the floor wire and front seat wire RH.
      GTY500520Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *a Front view of wire harness connector
      (to Occupant Detection ECU)
    2. Connect the cable to the negative (-) battery terminal.
    3. Turn the engine switch on (IG).
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      a15-7 (FSR+) - Body ground Engine switch on (IG) Below 1 V
      a15-4 (FSR-) - Body ground Engine switch on (IG) Below 1 V
    5. Turn the engine switch off.
    6. Disconnect the cable from the negative (-) battery terminal.
      WARNING:

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

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  13

    Result: 

    OK 

    See step  3

  3. CHECK WIRE HARNESS (OPEN) 
    1. Using a service wire, connect terminals 9 (FSR+) and 17 (FSR-) of connector B.
      GTY501577Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *3 Service Wire
      *a Front view of wire harness connector
      (to Airbag ECU 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
      a15-7 (FSR+) - a15-4 (FSR-) Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  12

    Result: 

    OK 

    See step  4

  4. CHECK WIRE HARNESS (SHORT) 
    1. Disconnect the service wire from connector B.
      GTY500520Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU 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
      a15-7 (FSR+) - a15-4 (FSR-) Always 1 MΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  11

    Result: 

    OK 

    See step  5

  5. CHECK WIRE HARNESS (SHORT TO GROUND) 
    1. Measure the resistance according to the value(s) in the table below.
      GTY500520Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *a Front view of wire harness connector
      (to Occupant Detection ECU)

      Standard Resistance

      Tester Connection Condition Specified Condition
      a15-7 (FSR+) - Body ground Always 1 MΩ or higher
      a15-4 (FSR-) - Body ground Always 1 MΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  10

    Result: 

    OK 

    See step  6

  6. CHECK DTC 
    1. Connect the connectors to the occupant detection ECU and airbag ECU assembly.
    2. Connect the cable to the negative (-) battery terminal.
    3. Clear the DTCs stored in the occupant detection ECU.

      Refer to DTC CHECK / CLEAR [09/2014 - ]

      Body Electrical > Occupant Detection > Clear DTCs 

    4. Clear the DTCs stored in the airbag ECU assembly.

      Refer to DTC CHECK / CLEAR [09/2014 - 03/2019]

      Body Electrical > SRS Airbag > Clear DTCs 

    5. Turn the engine switch off.
    6. Turn the engine switch on (IG), and wait for at least 10 seconds.
    7. Check for DTCs.

      Refer to DTC CHECK / CLEAR [09/2014 - ]

      Body Electrical > Occupant Detection > Trouble Codes 

      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 engine switch off.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [09/2014 - 08/2016]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [08/2016 - 11/2017]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [11/2017 - 03/2019] 

    Result: 

    NG 

    See step  7

  7. CHECK OCCUPANT DETECTION ECU 
    1. Disconnect the cable from the negative (-) battery terminal.
    2. Replace the occupant detection ECU with a known good one.

      Refer to REMOVAL [09/2014 - ]

      HINT: 

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

    3. Connect the cable to the negative (-) battery terminal.
    4. Clear the DTCs stored in the occupant detection ECU.

      Refer to DTC CHECK / CLEAR [09/2014 - ]

      Body Electrical > Occupant Detection > Clear DTCs 

    5. Clear the DTCs stored in the airbag ECU assembly.

      Refer to DTC CHECK / CLEAR [09/2014 - 03/2019]

      Body Electrical > SRS Airbag > Clear DTCs 

    6. Turn the engine switch off.
    7. Turn the engine switch on (IG), and wait for at least 10 seconds.
    8. Check for DTCs.

      Refer to DTC CHECK / CLEAR [09/2014 - ]

      Body Electrical > Occupant Detection > Trouble Codes 

      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 engine switch off.
    10. Disconnect the cable from the negative (-) battery terminal.
    11. Restore the occupant detection ECU that was installed for testing to its original location.

      Refer to REMOVAL [09/2014 - ]

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE AIRBAG ECU ASSEMBLY. Refer to  REMOVAL [09/2014 - ] 

    Result: 

    OK 

    See step  8

  8. REPLACE OCCUPANT DETECTION ECU 
    1. Turn the engine switch off.
    2. Disconnect the cable from the negative (-) battery terminal.
    3. Replace the occupant detection ECU with a new one.

      Refer to REMOVAL [09/2014 - ]

    4. Connect the cable to the negative (-) battery terminal.

      Result

      Proceed to
      NEXT

    Result: 

    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 [09/2014 - ]

      Body Electrical > Occupant Detection > Utility 

      Tester Display
      Zero Point Calibration & Sensitivity Check

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    END 

  10. CHECK FLOOR WIRE (SHORT TO GROUND) 
    1. Disconnect the front seat wire RH connector from the floor wire.
      GTY508328Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU 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
      Ta2-1 (FSR+) - Body ground Always 1 MΩ or higher
      Ta2-4 (FSR-) - Body ground Always 1 MΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    NG 

    REPLACE FLOOR WIRE 

  11. CHECK FLOOR WIRE (SHORT) 
    1. Disconnect the front seat wire RH connector from the floor wire.
      GTY508328Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU 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
      Ta2-1 (FSR+) - Ta2-4 (FSR-) Always 1 MΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    NG 

    REPLACE FLOOR WIRE 

  12. CHECK FLOOR WIRE (OPEN) 
    1. Disconnect the front seat wire RH connector from the floor wire.
      GTY512425Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *3 Front Seat Wire RH
      *4 Floor Wire
      *5 Service Wire
      *a Front view of wire harness connector
      (to Airbag ECU 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
      Ta2-1 (FSR+) - Ta2-4 (FSR-) Always Below 1 Ω
    3. Disconnect the service wire from connector B.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    NG 

    REPLACE FLOOR WIRE 

  13. CHECK FLOOR WIRE (SHORT TO B+) 
    1. Disconnect the front seat wire RH connector from the floor wire.
      GTY508328Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Occupant Detection ECU
      *2 Airbag ECU 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 (-) battery terminal.
    3. Turn the engine switch on (IG).
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      Ta2-1 (FSR+) - Body ground Engine switch on (IG) Below 1 V
      Ta2-4 (FSR-) - Body ground Engine switch on (IG) Below 1 V

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    NG 

    REPLACE FLOOR WIRE 

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