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DTC B1790 Center Airbag Sensor Assembly Communication Circuit Malfunction: Wiring Diagram

WARNING: This page is about a different car, the 2006 Lexus RX 400h. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Center Airbag Sensor Assembly Communication Wiring Diagram
G04114508Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

  1. CHECK DTC 
    1. Turn the ignition switch to the ON position.
    2. Clear the DTCs stored in memory (See DTC CHECK / CLEAR  ).

      HINT:

      First clear DTCs stored in the occupant classification ECU and then in the center airbag sensor assembly.

    3. Turn the ignition switch to the LOCK position.
    4. Turn the ignition switch to the ON position.
    5. Check the DTCs (See DTC CHECK / CLEAR  ).

      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.

    OK : USE SIMULATION METHOD TO CHECK 

    NG : GO TO NEXT STEP 

  2. CHECK CONNECTION OF CONNECTORS 
    1. Turn the ignition switch to the LOCK position.
    2. Disconnect the negative (-) terminal cable from the battery.
    3. Check that the connectors are properly connected to the occupant classification ECU and the center airbag sensor assembly.

      OK: The connectors are connected. 

    NG : CONNECT CONNECTORS, THEN GO TO STEP   1 

    OK : GO TO NEXT STEP 

  3. CHECK OCCUPANT CLASSIFICATION ECU CIRCUIT (SHORT TO B+) 
    1. Disconnect the connectors from the occupant classification ECU and the center airbag sensor assembly.
    2. Connect the negative (-) terminal cable to the battery.
    3. Turn the ignition switch to the ON position.
    4. Measure the voltage according to the value(s) in the table below.

      Voltage 

      VOLTAGE SPECIFIED CONDITIONS

      Tester connection Condition Specified condition
      O3-8 (FSR+) - Body ground Ignition switch ON Below 1 V
      O3-4 (FSR-) - Body ground Ignition switch ON Below 1 V

    NG : Go to step   12 

    Fig 2: View Of Air Bag Sensor Assembly And Connector Terminals
    G04114509Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    OK : GO TO NEXT STEP 

  4. CHECK OCCUPANT CLASSIFICATION ECU CIRCUIT (OPEN) 
    1. Turn the ignition switch to the LOCK position.
    2. Disconnect the negative (-) terminal cable from the battery, and wait for at least 90 seconds.
    3. Using a service wire, connect A21-1 (FSR+) and A21-2 (FSR-) of connector "B".
      NOTE: Do not forcibly insert a service wire into the terminals of the connector when connecting.
    4. Measure the resistance according to the value(s) in the table below.

      Resistance 

      RESISTANCE SPECIFIED CONDITIONS

      Tester connection Condition Specified condition
      O3-8 (FSR+) - O3-4 (FSR-) Always Below 1 Ω

    NG : Go to step   13 

    Fig 3: Identifying Occupant Classification ECU Circuit (Open)
    G04114510Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    OK : GO TO NEXT STEP 

  5. CHECK OCCUPANT CLASSIFICATION ECU CIRCUIT (SHORT) 
    1. Disconnect the service wire from connector "B".
    2. Measure the resistance according to the value(s) in the table below.

      Resistance 

      RESISTANCE SPECIFIED CONDITIONS

      Tester connection Condition Specified condition
      O3-8 (FSR+) - O3-4 (FSR-) Always 1 MΩ or higher

    NG : Go to step   14 

    Fig 4: View Of Air Bag Sensor Assembly And Connector Terminals
    G04114511Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    OK : GO TO NEXT STEP 

  6. CHECK OCCUPANT CLASSIFICATION ECU CIRCUIT (SHORT TO GROUND) 
    1. Measure the resistance according to the value(s) in the table below.

      Resistance 

      RESISTANCE SPECIFIED CONDITIONS

      Tester connection Condition Specified condition
      O3-8 (FSR+) - Body ground Always 1 MΩ or higher
      O3-4 (FSR-) - Body ground Always 1 MΩ or higher

    NG : Go to step   15 

    Fig 5: View Of Air Bag Sensor Assembly And Connector Terminals
    G04114512Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    OK : GO TO NEXT STEP 

  7. CHECK DTC 
    1. Connect the connectors to the occupant classification ECU and the center airbag sensor assembly.
    2. Connect the negative (-) terminal cable to the battery.
    3. Turn the ignition switch to the ON position.
    4. Clear the DTCs stored in memory (See DTC CHECK / CLEAR  ).

      HINT:

      First clear DTCs stored in the occupant classification ECU and then in the center airbag sensor assembly.

    5. Turn the ignition switch to the LOCK position.
    6. Turn the ignition switch to the ON position.
    7. Check the DTCs (See DTC CHECK / CLEAR  ).

      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.

    OK : USE SIMULATION METHOD TO CHECK 

    NG : GO TO NEXT STEP 

  8. REPLACE OCCUPANT CLASSIFICATION ECU 
    1. Turn the ignition switch to the LOCK position.
    2. Disconnect the negative (-) terminal cable from the battery.
    3. Replace the OCCUPANT CLASSIFICATION ECU  (See ).

      HINT:

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

  9. PERFORM ZERO POINT CALIBRATION 
    1. Connect the negative (-) terminal cable to the battery.
    2. Connect the intelligent tester to the DLC3.
    3. Turn the ignition switch to the ON position.
    4. Using the intelligent tester, perform "Zero point calibration" (See  1 ).

      OK: The "COMPLETED" is displayed. 

  10. PERFORM SENSITIVITY CHECK 
    1. Using the intelligent tester, perform "Sensitivity check" (See  1 ).

      Standard values: 27 to 33 kg (59.52 to 72.75 lb) 

  11. CHECK DTC 
    1. Turn the ignition switch to the ON position.
    2. Clear the DTCs stored in memory (See DTC CHECK / CLEAR  ).

      HINT:

      First clear DTCs stored in the occupant classification ECU and then in the center airbag sensor assembly.

    3. Turn the ignition switch to the LOCK position.
    4. Turn the ignition switch to the ON position.
    5. Check the DTCs (See DTC CHECK / CLEAR  ).

      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.

    NG : REPLACE CENTER AIRBAG SENSOR ASSEMBLY 

    OK : END 

  12. CHECK FLOOR WIRE (SHORT TO B+) 
    1. Turn the ignition switch to the LOCK position.
    2. Disconnect the negative (-) terminal cable from the battery, and wait for at least 90 seconds.
    3. Disconnect the floor wire connector from the front seat wire RH.
    4. Connect the negative (-) terminal cable to the battery, and wait for at least 2 seconds.
    5. Turn the ignition switch to the ON position.
    6. Measure the voltage according to the value(s) in the table below.

      Voltage 

      VOLTAGE SPECIFIED CONDITIONS

      Tester connection Condition Specified condition
      BJ1-1 (FSR+) - Body ground Ignition switch ON Below 1 V
      BJ1-4 (FSR-) - Body ground Ignition switch ON Below 1 V

    NG : REPAIR OR REPLACE FLOOR WIRE 

    Fig 6: View Of Air Bag Sensor Assembly And Connector Terminals
    G04114513Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    OK : REPAIR OR REPLACE FRONT SEAT WIRE RH 

  13. CHECK FLOOR WIRE (OPEN) 
    1. Disconnect the floor wire connector from the front seat wire RH.

      HINT:

      The service wire has already been inserted into the connector "B".

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

      Resistance 

      RESISTANCE SPECIFIED CONDITIONS

      Tester connection Condition Specified condition
      BJ1-1 (FSR+) - BJ1-4 (FSR-) Always Below 1 Ω

    NG : REPAIR OR REPLACE FLOOR WIRE 

    Fig 7: Identifying Floor Wire (Open)
    G04114514Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    OK : REPAIR OR REPLACE FRONT SEAT WIRE RH 

  14. CHECK FLOOR WIRE (SHORT) 
    1. Disconnect the floor wire connector from the front seat wire RH.
    2. Measure the resistance according to the value(s) in the table below.

      Resistance 

      RESISTANCE SPECIFIED CONDITIONS

      Tester connection Condition Specified condition
      BJ1-1 (FSR+) - BJ1-4 (FSR-) Always 1 MΩ or higher

    NG : REPAIR OR REPLACE FLOOR WIRE 

    Fig 8: View Of Air Bag Sensor Assembly And Connector Terminals
    G04114515Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    OK : REPAIR OR REPLACE FRONT SEAT WIRE RH 

  15. CHECK FLOOR WIRE (SHORT TO GROUND) 
    1. Disconnect the floor wire connector from the front seat wire RH.
    2. Measure the resistance according to the value(s) in the table below.

      Resistance 

      RESISTANCE SPECIFIED CONDITIONS

      Tester connection Condition Specified condition
      BJ1-1 (FSR+) - Body ground Always 1 MΩ or higher
      BJ1-4 (FSR-) - Body ground Always 1 MΩ or higher

    NG : REPAIR OR REPLACE FLOOR WIRE 

    Fig 9: View Of Air Bag Sensor Assembly And Connector Terminals
    G04114516Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    OK : REPAIR OR REPLACE FRONT SEAT WIRE RH 

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