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DTC B1790: Center Airbag Sensor Assembly Communication Circuit Malfunction (FROM 12/2010): Procedure

WARNING: This page is about a different car, the 2011 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
  1. CHECK DTC 
    1. Turn the ignition 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 assembly. Refer to DTC CHECK / CLEAR .
    4. Turn the ignition switch off.
    5. Turn the ignition switch on (IG).
    6. Check 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.

    OK → USE SIMULATION METHOD TO CHECK 

    NG: Go to next step 

  2. CHECK CONNECTION OF CONNECTORS 
    1. Turn the ignition 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 assembly.

      OK

      The connectors are properly connected.

    NG → CONNECT CONNECTORS PROPERLY, THEN GO TO STEP  1 

    OK: Go to next step 

  3. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT TO B+) 
    1. Disconnect the connector from the center airbag sensor assembly and occupant classification ECU.
      Fig 1: Checking Occupant Classification System Circuit (Short To B+)
      GTY201743Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Connect the negative (-) terminal cable to the battery.
    3. Turn the ignition switch on (IG).
    4. Measure the voltage according to the value(s) in the table below.

      Standard voltage

      Tester connection Condition Specified condition
      O4-8 (FSR+) - Body ground Ignition switch on (IG) Below 1 V
      O4-4 (FSR-) - Body ground Ignition switch on (IG) Below 1 V

    NG → See step   12 

    OK: Go to next step 

  4. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (OPEN) 
    1. Turn the ignition switch off.
      Fig 2: Checking Occupant Classification System Circuit (Open)
      GTY201742Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Disconnect the negative (-) terminal cable from the battery.
    3. Using a service wire, connect terminals 12 (FSP+) and 13 (FSP-) 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.

      Standard resistance

      Tester connection Condition Specified condition
      O4-8 (FSR+) - O4-4 (FSR-) Always Below 1 Ω

    NG → See step   13 

    OK: Go to next step 

  5. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT) 
    1. Disconnect the service wire from connector B.
      Fig 3: Checking Occupant Classification System Circuit (Short)
      GTY201743Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the resistance according to the value(s) in the table below.

      Standard resistance

      Tester connection Condition Specified condition
      O4-8 (FSR+) - O4-4 (FSR-) Always 1 MΩ or Higher

    NG → See step   14 

    OK: Go to next step 

  6. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT TO GROUND) 
    1. Measure the resistance according to the value(s) in the table below.
      Fig 4: Checking Occupant Classification System Circuit (Short To Ground)
      GTY201743Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      Standard resistance

      Tester connection Condition Specified condition
      O4-8 (FSR+) - Body ground Always 1 MΩ or Higher
      O4-4 (FSR-) - Body ground Always 1 MΩ or Higher

    NG → See step   15 

    OK: Go to next step 

  7. RECHECK DTC 
    1. Connect the connectors to the occupant classification ECU and the center airbag sensor assembly.
    2. Connect the Techstream to the DLC3.
    3. Connect the negative (-) terminal cable to the battery.
    4. Turn the ignition 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 assembly. Refer to DTC CHECK / CLEAR .
    7. Turn the ignition switch off.
    8. Turn the ignition switch on (IG).
    9. Using the Techstream, check 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 → USE SIMULATION METHOD TO CHECK 

    NG: Go to next step 

  8. REPLACE OCCUPANT CLASSIFICATION ECU 
    1. Turn the ignition switch off.
    2. Disconnect the negative (-) terminal cable from the battery, and wait for at least 90 seconds.
    3. Replace the occupant classification ECU. Refer to REMOVAL .

      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 the Techstream to the DLC3.
    3. Turn the ignition switch on (IG).
    4. Using the Techstream, perform "Zero point calibration". Refer to INITIALIZATION .

      OK

      "Zero Point Calibration is complete." is displayed.

    NEXT: Go to next step 

  10. PERFORM SENSITIVITY CHECK 
    1. Using the Techstream, perform "Sensitivity check". Refer to DTC CHECK / CLEAR .

      Standard value

      27 to 33 kg (59.52 to 72.75 lb)

    NEXT: Go to next step 

  11. RECHECK DTC 
    1. Turn the ignition 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 assembly. Refer to DTC CHECK / CLEAR .
    4. Turn the ignition switch off.
    5. Turn the ignition switch on (IG).
    6. Using the Techstream, check 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   16 

    OK → END 

  12. CHECK FLOOR WIRE NO. 2 (SHORT TO B+) 
    1. Turn the ignition switch off.
      Fig 5: Checking Floor Wire No. 2 Terminals (Short To B+)
      GTY303301Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    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 No. 2.
    4. Connect the negative (-) terminal cable to the battery, and wait for at least 2 seconds.
    5. Turn the ignition switch on (IG).
    6. Measure the voltage according to the value(s) in the table below.

      Standard voltage

      Tester connection Condition Specified condition
      LO2-1 (FSR+) - Body ground Ignition switch on (IG) Below 1 V
      LO2-4 (FSR-) - Body ground Ignition switch on (IG) Below 1 V

    NG → REPAIR OR REPLACE FLOOR WIRE NO. 2 

    OK → REPAIR OR REPLACE FRONT SEAT WIRE RH 

  13. CHECK FLOOR WIRE NO. 2 (OPEN) 
    1. Disconnect the front seat wire RH connector from the floor wire No. 2.
      Fig 6: Checking Floor Wire No. 2 Terminals (Open)
      GTY304397Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      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
      LO2-1 (FSR+) - LO2-4 (FSR-) Always Below 1 Ω

    NG → REPAIR OR REPLACE FLOOR WIRE NO. 2 

    OK → REPAIR OR REPLACE FRONT SEAT WIRE RH 

  14. CHECK FLOOR WIRE NO. 2 (SHORT) 
    1. Disconnect the front seat wire RH connector from the floor wire No. 2.
      Fig 7: Checking Floor Wire No. 2 Terminals (Short)
      GTY303301Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the resistance according to the value(s) in the table below.

      Standard resistance

      Tester connection Condition Specified condition
      LO2-1 (FSR+) - LO2-4 (FSR-) Always 1 MΩ or Higher

    NG → REPAIR OR REPLACE FLOOR WIRE NO. 2 

    OK → REPAIR OR REPLACE FRONT SEAT WIRE RH 

  15. CHECK FLOOR WIRE NO. 2 (SHORT TO GROUND) 
    1. Disconnect the front seat wire RH connector from the floor wire No. 2.
      Fig 8: Checking Floor Wire No. 2 Terminals (Short To Ground)
      GTY303301Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the resistance according to the value(s) in the table below.

      Standard resistance

      Tester connection Condition Specified condition
      LO2-1 (FSR+) - Body ground Always 1 MΩ or Higher
      LO2-4 (FSR-) - Body ground Always 1 MΩ or Higher

    NG → REPAIR OR REPLACE FLOOR WIRE NO. 2 

    OK → REPAIR OR REPLACE FRONT SEAT WIRE RH 

  16. REPLACE CENTER AIRBAG SENSOR ASSEMBLY. Refer to  REMOVAL 
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