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

WARNING: This page is about a different car, the 2010 Lexus GS 450h. However, it is still accessible from the selected car via links, so may be relevant.
  1. CHECK FOR DTC 
    1. Turn the power switch ON (IG).
    2. Clear the DTCs stored in the occupant classification ECU. Refer to DTC CHECK / CLEAR .
    3. Clear the DTCs stored in the center airbag sensor. Refer to DATA LIST / ACTIVE TEST .
    4. Turn the power switch OFF.
    5. Turn the power switch ON (IG).
    6. Check for the DTCs. Refer to 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 → See step   2 

    OK → See step   11 

  2. CHECK CONNECTION OF CONNECTOR 
    1. Turn the power switch OFF.
    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.

      OK

      Connectors are properly connected.

    NG → CONNECT CONNECTORS PROPERLY 

    OK: Go to next step 

  3. CHECK CONNECTOR 
    1. Disconnect the connectors from the center airbag sensor and the occupant classification ECU.
    2. Check that the connectors (on the center airbag sensor side and occupant classification ECU side) are not damaged.

      OK

      Connectors are not deformed or damaged.

    NG → REPAIR OR REPLACE WIRE HARNESS 

    OK: Go to next step 

  4. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT 
    Fig 1: Identifying Occupant Classification ECU Connector Terminal a17
    GTY107685Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    1. Connect the negative (-) terminal cable to the battery.
    2. Turn the power switch ON (IG).
    3. Measure the voltage according to the value(s) in the table below.

      Standard voltage

      Tester Connection Switch Condition Specified Condition
      a17-11 (FSR+) - Body ground Power switch ON (IG) Below 1 V
      a17-12 (FSR-) - Body ground
    4. Turn the power switch OFF.
    5. Disconnect the negative (-) terminal cable from the battery.
    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 when connecting the wire.

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

      Standard resistance

      Tester Connection Switch Condition Specified Condition
      a17-11 (FSR+) - a17-12 (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 Switch Condition Specified Condition
      a17-11 (FSR+) - a17-12 (FSR-) Always 1 MΩ or higher
      a17-11 (FSR+) - Body ground
      a17-12 (FSR-) - Body ground

    NG → See step   10 

    OK: Go to next step 

  5. CHECK FOR DTC 
    1. Connect the connectors to the occupant classification ECU and the center airbag sensor.
    2. Connect the Techstream to the DLC3.
    3. Connect the negative (-) terminal cable to the battery.
    4. Turn the power switch ON (IG).
    5. Clear the DTCs stored in the occupant classification ECU. Refer to DTC CHECK / CLEAR .
    6. Clear the DTCs stored in the center airbag sensor. Refer to DTC CHECK / CLEAR .
    7. Turn the power switch OFF.
    8. Turn the power switch ON (IG).
    9. Using the Techstream, check for the DTCs of the occupant classification ECU. Refer to 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 → See step   6 

    OK → See step   11 

  6. REPLACE OCCUPANT CLASSIFICATION ECU 
    1. Connect the Techstream to the DLC3.
    2. Turn the power switch ON (IG).
    3. Using the Techstream, save the ECU data from the ECU which has been installed on the vehicle. Refer to REGISTRATION .
    4. Turn the power switch OFF.
    5. Disconnect the negative (-) terminal cable from the battery, and wait for at least 90 seconds.
    6. Replace the occupant classification ECU. Refer to DISASSEMBLY .
    7. Connect the negative (-) terminal cable to the battery.
    8. Turn the power switch ON (IG).
    9. Using the Techstream, load the previous ECU data stored into the new ECU. Refer to REGISTRATION .
    10. Turn the power switch OFF.
    11. Turn the power switch ON (IG).
    12. Clear the DTCs stored in the memory. Refer to DTC CHECK / CLEAR .

      HINT: 

      If the DTCs are not cleared at this time, past DTCs will remain.

    NEXT: Go to next step 

  7. CHECK FOR DTC 
    1. Turn the power switch ON (IG).
    2. Clear the DTCs stored in the occupant classification ECU. Refer to DTC CHECK / CLEAR .
    3. Clear the DTCs stored in the center airbag sensor. Refer to DTC CHECK / CLEAR .
    4. Turn the power switch OFF.
    5. Turn the power switch ON (IG).
    6. Using the Techstream, check for the DTCs of the occupant classification ECU. Refer to 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 → See step   9 

    NG: Go to next step 

  8. REPLACE CENTER AIRBAG SENSOR ASSEMBLY 
    1. Turn the power switch OFF.
    2. Disconnect the negative (-) terminal cable from the battery, and wait for at least 90 seconds.
    3. Replace the center airbag sensor. Refer to REMOVAL .

    NEXT: Go to next step 

  9. PERFORM SENSITIVITY CHECK 
    1. Perform the sensitivity check. Refer to INITIALIZATION .

    NEXT → END 

  10. CHECK FLOOR WIRE 
    Fig 2: Checking Floor Wire
    GTY107686Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    1. Turn the power switch OFF.
    2. Disconnect the negative (-) terminal cable from the battery, and wait for at least 90 seconds.
    3. Disconnect the front seat wire RH connector from the floor wire.
    4. Connect the negative (-) terminal cable to the battery, and wait for at least 2 seconds.
    5. Turn the power switch ON (IG).
    6. Measure the voltage according to the value(s) in the table below.

      Standard voltage

      Tester Connection Switch Condition Specified Condition
      Ua2-2 (FSR+) - Body ground Power switch ON (IG) Below 1 V
      Ua2-3 (FSR-) - Body ground
    7. Turn the power switch OFF.
    8. Disconnect the negative (-) terminal cable from the battery.
    9. 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 when connecting the wire.

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

      Standard resistance

      Tester Connection Switch Condition Specified Condition
      Ua2-2 (FSR+) - Ua2-3 (FSR-) Always Below 1 Ω
    11. Disconnect the service wire from connector B.
    12. Measure the resistance according to the value(s) in the table below.

      Standard resistance

      Tester Connection Switch Condition Specified Condition
      Ua2-2 (FSR+) - Ua2-3 (FSR-) Always 1 MΩ or higher
      Ua2-2 (FSR+) - Body ground
      Ua2-3 (FSR-) - Body ground

    NG → REPAIR OR REPLACE FLOOR WIRE 

    OK → REPAIR OR REPLACE FRONT SEAT WIRE RH 

  11. USE SIMULATION METHOD TO CHECK. Refer to  DIAGNOSIS SYSTEM 
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