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DTC B1790: Center Airbag Sensor Assembly Communication Circuit Malfunction: Procedure

WARNING: This page is about a different car, the 2010 Toyota FJ Cruiser. However, it is still accessible from the selected car via links, so may be relevant.
  1. CHECK DTC 
    1. Turn the ignition switch to the on position.
    2. Clear the DTCs stored in the memory. Refer toDTC 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. Refer toDTC 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 → See step   12 

    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, and wait for at least 90 seconds.
    3. Check that the connectors are properly connected to the occupant classification ECU and the center airbag sensor assembly.

      OK

      The connectors are properly connected.

    NG → CONNECT CONNECTORS 

    OK: Go to next step 

  3. CHECK CENTER AIRBAG SENSOR CIRCUIT (TO B+) 
    1. Disconnect the connectors from the occupant classification ECU and the center airbag sensor assembly.
      Fig 1: Identifying Occupant Classification ECU, Center Airbag Sensor, Floor Wire (B+) & Connector Terminals
      GTY210258Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Connect the negative (-) terminal cable to the battery.
    3. Turn the ignition switch to the on position.
    4. Measure the voltage.

      Standard voltage

      Tester connection Condition Specified condition
      Q4-8 (FSR+) -
      Body ground      		 Ignition switch on Below 1 V
      Q4-4 (FSR-) -
      Body ground      		 Ignition switch on Below 1 V

    NG → See step   14 

    OK: Go to next step 

  4. CHECK CENTER AIRBAG SENSOR CIRCUIT (FOR OPEN) 
    1. Turn the ignition switch to the lock position.
      Fig 2: Checking Center Airbag Sensor Circuit (For Open)
      GTY169176Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Disconnect the negative (-) terminal cable from the battery, and wait for at least 90 seconds.
    3. Using a service wire, connect K1-16 (FSP+) and K1-24 (FSP-) of connector B.
      NOTE:

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

    4. Measure the resistance.

      Standard resistance

      Tester connection Condition Specified condition
      Q4-8 (FSR+) -
      Q4-4 (FSR-)      		 Always Below 1 Ω

    NG → See step   15 

    OK: Go to next step 

  5. CHECK CENTER AIRBAG SENSOR CIRCUIT (FOR SHORT) 
    1. Disconnect the service wire from connector B.
      Fig 3: Identifying Occupant Classification ECU, No. 1 Seat Wire, Floor Wire (To Ground) & Connector Terminals
      GTY210258Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the resistance.

      Standard resistance

      Tester connection Condition Specified condition
      Q4-8 (FSR+) -
      Q4-4 (FSR-)      		 Always 1 MΩ or higher

    NG → See step   16 

    OK: Go to next step 

  6. CHECK CENTER AIRBAG SENSOR CIRCUIT (TO GROUND) 
    1. Measure the resistance.
      Fig 4: Identifying Occupant Classification ECU, No. 1 Seat Wire, Floor Wire (To Ground) & Connector Terminals
      GTY210258Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      Standard resistance

      Tester connection Condition Specified condition
      Q4-8 (FSR+) -
      Body ground      		 Always 1 MΩ or higher
      Q4-4 (FSR-) -
      Body ground      		 Always 1 MΩ or higher

    NG → See step   17 

    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 the memory. Refer toDTC 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. Refer toDTC 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 → See step   12 

    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, and wait for at least 90 seconds.
    3. Replace the occupant classification ECU. Refer toREMOVAL .

      HINT: 

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

    NEXT: Go to next step 

  9. PERFORM ZERO POINT CALIBRATION 
    1. Connect the negative (-) terminal cable to the battery.
    2. Connect a Techstream to the DLC3.
    3. Turn the ignition switch to the on position.
    4. Using the Techstream, perform the zero point calibration. Refer toINITIALIZATION .

      OK

      COMPLETED is displayed.

    NEXT: Go to next step 

  10. PERFORM SENSITIVITY CHECK 
    1. Using a Techstream, perform the sensitivity check. Refer toINITIALIZATION .
      1. Confirm that nothing is placed on the passenger seat.
      2. Confirm that the beginning sensor reading is within the standard range.

        Standard range

        -3.2 to 3.2 kg (-7 to 7 lb)

      3. Place a 30 kg (66.14 lb) weight (e.g. a lead mass) onto the front passenger seat.
      4. Confirm that the sensitivity is within the standard range.

        Standard range

        27 to 33 kg (59.52 to 72.75 lb)

        HINT: 

        When performing the sensitivity check, use a solid metal weight (the check result may not be accurate if a liquid weight is used).

    NEXT: Go to next step 

  11. CHECK DTC 
    1. Turn the ignition switch to the on position.
    2. Clear the DTCs stored in the memory. Refer toDTC 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. Refer toDTC 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 → See step   13 

    OK → END 

  12. USE SIMULATION METHOD TO CHECK. Refer to DIAGNOSIS SYSTEM 
  13. REPLACE CENTER AIRBAG SENSOR ASSEMBLY. Refer to REMOVAL 
  14. CHECK FLOOR WIRE (TO B+) 
    1. Turn the ignition switch to the lock position.
      Fig 5: Identifying Occupant Classification ECU, No. 1 Seat Wire & Floor Wire (To B+) & Connector Terminals
      GTY210259Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Disconnect the negative (-) terminal cable from the battery, and wait for at least 90 seconds.
    3. Disconnect the connectors from the floor wire and the No. 1 seat wire.
    4. Connect the negative (-) terminal cable to the battery.
    5. Turn the ignition switch to the on position.
    6. Measure the voltage.

      Standard voltage

      Tester connection Condition Specified condition
      KQ1-1 (FSR+) -
      Body ground      		 Ignition switch on Below 1 V
      KQ1-4 (FSR-) -
      Body ground      		 Ignition switch on Below 1 V

    NG → REPAIR OR REPLACE FLOOR WIRE 

    OK → REPLACE NO. 1 SEAT WIRE 

  15. CHECK FLOOR WIRE (FOR OPEN) 
    1. Disconnect the connectors from the floor wire and the No. 1 seat wire.

      HINT: 

      The service wire has already been inserted into connector B.

      Fig 6: Checking Floor Wire (For Open)
      GTY172333Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the resistance.

      Standard resistance

      Tester connection Condition Specified condition
      KQ1-1 (FSR+) -
      KQ1-4 (FSR-)      		 Always Below 1 Ω

    NG → REPAIR OR REPLACE FLOOR WIRE 

    OK → REPLACE NO. 1 SEAT WIRE 

  16. CHECK FLOOR WIRE (FOR SHORT) 
    1. Disconnect the connectors from the floor wire and the No. 1 seat wire.
      Fig 7: Identifying Occupant Classification ECU, No. 1 Seat Wire, Floor Wire (For Short) & Connector Terminals
      GTY210259Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the resistance.

      Standard resistance

      Tester connection Condition Specified condition
      KQ1-1 (FSR+) -
      KQ1-4 (FSR-)      		 Always 1 MΩ or higher

    NG → REPAIR OR REPLACE FLOOR WIRE 

    OK → REPLACE NO. 1 SEAT WIRE 

  17. CHECK FLOOR WIRE (TO GROUND) 
    1. Disconnect the connectors from the floor wire and the No. 1 seat wire.
      Fig 8: Identifying Occupant Classification ECU, No. 1 Seat Wire, Floor Wire (To Ground) & Connector Terminals
      GTY210259Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the resistance.

      Standard resistance

      Tester connection Condition Specified condition
      KQ1-1 (FSR+) -
      Body ground      		 Always 1 MΩ or higher
      KQ1-4 (FSR-) -
      Body ground      		 Always 1 MΩ or higher

    NG → REPAIR OR REPLACE FLOOR WIRE 

    OK → REPLACE NO. 1 SEAT WIRE 

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