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DTC B1773: Belt Tension Sensor Circuit Malfunction; DTC B1776: Seat Belt Tension Sensor Power Source Circuit Malfunction: Procedure

WARNING: This page is about a different car, the 2012 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.
  1. CHECK CONNECTORS 
    1. Turn the ignition switch off.
    2. Disconnect the cable from the negative (-) battery terminal.
    3. Check that the connectors are properly connected to the occupant classification ECU and the seat belt tension sensor.

      OK

      The connectors are properly connected.

      HINT: 

      If the connectors are not connected securely, reconnect the connectors and proceed to the next inspection.

    4. Disconnect the connectors from the occupant classification ECU and the seat belt tension sensor.
    5. Check that the terminals of the connectors are not damaged.

      OK

      The terminals are not deformed or damaged.

    NG → REPLACE WIRE HARNESS 

    OK: Go to next step 

  2. CHECK SEAT BELT TENSION SENSOR CIRCUIT (SHORT TO B+) 
    1. Connect the cable to the negative (-) battery terminal.
      Fig 1: Checking Seat Belt Tension Sensor Circuit
      GTY180499Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Turn the ignition switch to ON.
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      R2-8 (GBT) - Body ground Ignition switch ON Below 1 V
      R2-16 (BT) - Body ground Ignition switch ON Below 1 V
      R2-17 (VBT) - Body ground Ignition switch ON Below 1 V

    NG → See step   10 

    OK: Go to next step 

  3. CHECK SEAT BELT TENSION SENSOR CIRCUIT (OPEN) 
    1. Turn the ignition switch off.
      Fig 2: Checking Seat Belt Tension Sensor Circuit (Open)
      GTY170100Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Disconnect the cable from the negative (-) battery terminal.
    3. Using SST, connect terminals 1 (GBT) and 3 (BT), and connect terminals 2 (VBT) and 3 (BT) of connector E.
      NOTE:

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

      • SST: 09843-18040 
    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      R2-16 (BT) - R2-8 (GBT) Always Below 1 Ω
      R2-17 (VBT) - R2-16 (BT) Always Below 1 Ω

    NG → See step   11 

    OK: Go to next step 

  4. CHECK SEAT BELT TENSION SENSOR CIRCUIT (SHORT TO GROUND) 
    1. Disconnect SST from connector E.
      Fig 3: Checking Seat Belt Tension Sensor Circuit
      GTY180499Courtesy 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
      R2-8 (GBT) - Body ground Always 1 MΩ or higher
      R2-16 (BT) - Body ground Always 1 MΩ or higher
      R2-17 (VBT) - Body ground Always 1 MΩ or higher

    NG → See step   12 

    OK: Go to next step 

  5. CHECK SEAT BELT TENSION SENSOR CIRCUIT (SHORT) 
    1. Measure the resistance according to the value(s) in the table below.
      Fig 4: Checking Seat Belt Tension Sensor Circuit
      GTY180499Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      Standard Resistance

      Tester Connection Condition Specified Condition
      R2-16 (BT) - R2-8 (GBT) Always 1 MΩ or higher
      R2-17 (VBT) - R2-16 (BT) Always 1 MΩ or higher

    NG → See step   13 

    OK: Go to next step 

  6. CHECK FOR DTC 
    1. Connect the connectors to the occupant classification ECU and the seat belt tension sensor.
    2. Connect the cable to the negative (-) battery terminal.
    3. Turn the ignition switch to ON.
    4. Clear the DTCs stored in the occupant classification ECU. Refer to DTC CHECK / CLEAR .
    5. Clear the DTCs stored in the center airbag sensor assembly. Refer to DTC CHECK / CLEAR .
    6. Turn the ignition switch off.
    7. Turn the ignition switch to ON.
    8. Check for DTCs. Refer to DTC CHECK / CLEAR .

      OK

      DTC B1773 and B1776 are not output.

      HINT: 

      Codes other than B1773 and B1776 may be output at this time, but they are not related to this check.

    NG → See step   7 

    OK → See step   14 

  7. INSPECT FRONT SEAT OUTER BELT ASSEMBLY RH 
    1. Turn the ignition switch off.
    2. Disconnect the cable from the negative (-) battery terminal.
    3. Replace the front seat outer belt assembly RH with a known good part. Refer to REMOVAL .

      HINT: 

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

    4. Connect the cable to the negative (-) battery terminal.
    5. Turn the ignition switch to ON.
    6. Clear the DTCs stored in the occupant classification ECU. Refer to DTC CHECK / CLEAR .
    7. Clear the DTCs stored in the center airbag sensor assembly. Refer to DTC CHECK / CLEAR .
    8. Turn the ignition switch off.
    9. Turn the ignition switch to ON.
    10. Check for DTCs. Refer to DTC CHECK / CLEAR .

      OK

      DTC B1773 and B1776 are not output.

      HINT: 

      Codes other than B1773 and B1776 may be output at this time, but they are not related to this check.

    NG → See step   8 

    OK → END 

  8. REPLACE OCCUPANT CLASSIFICATION ECU 
    1. Connect the Techstream to the DLC3.
    2. Turn the ignition switch to ON.
    3. Using the Techstream, save the ECU data from the ECU currently installed on the vehicle. Refer to REGISTRATION .
    4. Turn the ignition switch off.
    5. Disconnect the cable from the negative (-) battery terminal.
    6. Replace the occupant classification ECU. Refer to REMOVAL .
    7. Connect the cable to the negative (-) battery terminal.
    8. Turn the ignition switch to ON.
    9. Using the Techstream, load the previous ECU data stored into the new ECU. Refer to REGISTRATION .
    10. Turn the ignition switch off.
    11. Turn the ignition switch to ON.
    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 

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

    NEXT → END 

  10. CHECK FRONT SEAT WIRE RH (SHORT TO B+) 
    1. Turn the ignition switch off.
      Fig 5: Checking Front Seat Wire RH
      GTY168514Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Disconnect the cable from the negative (-) battery terminal.
    3. Disconnect the No. 2 floor wire connector from the front seat wire RH.
    4. Connect the cable to the negative (-) battery terminal.
    5. Turn the ignition switch to ON.
    6. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      R2-8 (GBT) - Body ground Ignition switch ON Below 1 V
      R2-16 (BT) - Body ground Ignition switch ON Below 1 V
      R2-17 (VBT) - Body ground Ignition switch ON Below 1 V

    NG → REPLACE FRONT SEAT WIRE RH 

    OK → REPLACE NO. 2 FLOOR WIRE 

  11. CHECK FRONT SEAT WIRE RH (OPEN) 
    1. Disconnect the No. 2 floor wire connector from the front seat wire RH.
      Fig 6: Checking Front Seat Wire RH (Open)
      GTY188212Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Using SST, connect terminals 4 (BT) and 8 (GBT), and connect terminals 4 (BT) and 9 (VBT) of connector C.
      NOTE:

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

      • SST: 09843-18040 
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      R2-16 (BT) - R2-8 (GBT) Always Below 1 Ω
      R2-16 (BT) - R2-17 (VBT) Always Below 1 Ω

    NG → REPLACE FRONT SEAT WIRE RH 

    OK → REPLACE NO. 2 FLOOR WIRE 

  12. CHECK FRONT SEAT WIRE RH (SHORT TO GROUND) 
    1. Disconnect the No. 2 floor wire connector from the front seat wire RH.
      Fig 7: Checking Front Seat Wire RH
      GTY168514Courtesy 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
      R2-8 (GBT) - Body ground Always 1 MΩ or higher
      R2-16 (BT) - Body ground Always 1 MΩ or higher
      R2-17 (VBT) - Body ground Always 1 MΩ or higher

    NG → REPLACE FRONT SEAT WIRE RH 

    OK → REPLACE NO. 2 FLOOR WIRE 

  13. CHECK FRONT SEAT WIRE RH (SHORT) 
    1. Disconnect the No. 2 floor wire connector from the front seat wire RH.
      Fig 8: Checking Front Seat Wire RH
      GTY168514Courtesy 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
      R2-16 (BT) - R2-8 (GBT) Always 1 MΩ or higher
      R2-17 (VBT) - R2-16 (BT) Always 1 MΩ or higher

    NG → REPLACE FRONT SEAT WIRE RH 

    OK → REPLACE NO. 2 FLOOR WIRE 

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