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

WARNING: This page is about a different variant/trim than selected.
  1. CHECK CONNECTORS 
    1. Turn the power switch off.
    2. Disconnect the cable from the negative (-) auxiliary battery terminal.
      WARNING:

      Wait at least 90 seconds after disconnecting the cable from the negative (-) auxiliary battery terminal to disable the SRS system.

    3. Check that the connectors are properly connected to the airbag ECU assembly and occupant detection ECU. Also check that the connectors that link the front seat wire RH and No. 2 floor wire are properly connected.

      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 airbag ECU assembly and occupant detection ECU. Also disconnect the connectors that link the front seat wire RH and No. 2 floor wire.
    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 OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT TO B+) 
    1. Connect the connectors that link the No. 2 floor wire and front seat wire RH.
      Fig 1: Checking Occupant Classification System Circuit For Short To B+
      GTY328702Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Connect the cable to the negative (-) auxiliary battery terminal.
    3. Turn the power switch on (IG).
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      W3-8 (FSR+) - Body ground Power switch on (IG) Below 1 V
      W3-4 (FSR-) - Body ground Power switch on (IG) Below 1 V
    5. Turn the power switch off.
    6. Disconnect the cable from the negative (-) auxiliary battery terminal.
      WARNING:

      Wait at least 90 seconds after disconnecting the cable from the negative (-) auxiliary battery terminal to disable the SRS system.

      TEXT IN ILLUSTRATION

      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *a Front view of wire harness connector
      (to Occupant Detection ECU)

    NG → See step   11 

    OK: Go to next step 

  3. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (OPEN) 
    1. Using a service wire, connect terminals 12 (FSR+) and 13 (FSR-) of connector B.
      Fig 2: Checking Occupant Classification System For Open Circuit
      GTY332059Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      NOTE:

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

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

      Standard Resistance

      Tester Connection Condition Specified Condition
      W3-8 (FSR+) - W3-4 (FSR-) Always Below 1 Ω
      TEXT IN ILLUSTRATION

      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *3 Service Wire
      *a Front view of wire harness connector
      (to Airbag ECU Assembly)
      *b Front view of wire harness connector
      (to Occupant Detection ECU)

    NG → See step   12 

    OK: Go to next step 

  4. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT) 
    1. Disconnect the service wire from connector B.
      Fig 3: Checking Occupant Classification System For Short
      GTY328702Courtesy 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
      W3-8 (FSR+) - W3-4 (FSR-) Always 1 MΩ or higher
      TEXT IN ILLUSTRATION

      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *a Front view of wire harness connector
      (to Occupant Detection ECU)

    NG → See step   13 

    OK: Go to next step 

  5. 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 For Short To Ground
      GTY328702Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      Standard Resistance

      Tester Connection Condition Specified Condition
      W3-8 (FSR+) - Body ground Always 1 MΩ or higher
      W3-4 (FSR-) - Body ground Always 1 MΩ or higher
      TEXT IN ILLUSTRATION

      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *a Front view of wire harness connector
      (to Occupant Detection ECU)

    NG → See step   14 

    OK: Go to next step 

  6. CHECK DTC 
    1. Connect the connectors to the occupant detection ECU and airbag ECU assembly.
    2. Connect the cable to the negative (-) auxiliary battery terminal.
    3. Turn the power switch on (IG).
    4. Clear the DTCs stored in the occupant detection ECU. Refer to DTC CHECK / CLEAR .
    5. Clear the DTCs stored in the airbag ECU assembly. Refer to DTC CHECK / CLEAR .
    6. Turn the power switch off.
    7. Turn the power switch on (IG).
    8. Check for 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.

    9. Turn the power switch off.

    NG → See step   7 

    OK → See step   15 

  7. CHECK OCCUPANT DETECTION ECU 
    1. Disconnect the cable from the negative (-) auxiliary battery terminal.
    2. Replace the occupant detection ECU with a known good one. Refer to REMOVAL .

      HINT: 

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

    3. Connect the cable to the negative (-) auxiliary battery terminal.
    4. Clear the DTCs stored in the occupant detection ECU. Refer to DTC CHECK / CLEAR .
    5. Clear the DTCs stored in the airbag ECU assembly. Refer to DTC CHECK / CLEAR .
    6. Turn the power switch off.
    7. Turn the power switch on (IG).
    8. Check for 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.

    9. Turn the power switch off.
    10. Disconnect the cable from the negative (-) auxiliary battery terminal.
    11. Return the occupant detection ECU that was installed for testing to its original location. Refer to REMOVAL .

    NG → See step   16 

    OK: Go to next step 

  8. REPLACE OCCUPANT DETECTION ECU 
    1. Disconnect the cable from the negative (-) auxiliary battery terminal.
    2. Replace the occupant detection ECU with a new one. Refer to REMOVAL .
    3. Connect the cable to the negative (-) auxiliary battery terminal.

    NEXT: Go to next step 

  9. PERFORM ZERO POINT CALIBRATION 
    1. Using the Techstream, perform Zero Point Calibration. Refer to INITIALIZATION .

    NEXT: Go to next step 

  10. PERFORM SENSITIVITY CHECK 
    1. Using the Techstream, perform Sensitivity Check. Refer to INITIALIZATION .

    NEXT → END 

  11. CHECK NO. 2 FLOOR WIRE (SHORT TO B+) 
    1. Disconnect the front seat wire RH connector from the No. 2 floor wire.
      Fig 5: Checking No. 2 Floor Wire For Short To B+
      GTY338973Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Connect the cable to the negative (-) auxiliary battery terminal.
    3. Turn the power switch on (IG).
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      SW1-1 (FSR+) - Body ground Power switch on (IG) Below 1 V
      SW1-4 (FSR-) - Body ground Power switch on (IG) Below 1 V
      TEXT IN ILLUSTRATION

      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *3 Front Seat Wire RH
      *4 No. 2 Floor Wire
      *a Front view of wire harness connector
      (to Front Seat Wire RH)

    NG → REPLACE NO. 2 FLOOR WIRE 

    OK → REPLACE FRONT SEAT WIRE RH 

  12. CHECK NO. 2 FLOOR WIRE (OPEN) 
    1. Disconnect the front seat wire RH connector from the No. 2 floor wire.
      Fig 6: Checking No. 2 Floor Wire For Open
      GTY344077Courtesy 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
      SW1-1 (FSR+) - SW1-4 (FSR-) Always Below 1 Ω
    3. Disconnect the service wire from connector B.
      TEXT IN ILLUSTRATION

      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *3 Front Seat Wire RH
      *4 No. 2 Floor Wire
      *5 Service Wire
      *a Front view of wire harness connector
      (to Airbag ECU Assembly)
      *b Front view of wire harness connector
      (to Front Seat Wire RH)

    NG → REPLACE NO. 2 FLOOR WIRE 

    OK → REPLACE FRONT SEAT WIRE RH 

  13. CHECK NO. 2 FLOOR WIRE (SHORT) 
    1. Disconnect the front seat wire RH connector from the No. 2 floor wire.
      Fig 7: Checking No. 2 Floor Wire For Short
      GTY338973Courtesy 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
      SW1-1 (FSR+) - SW1-4 (FSR-) Always 1 MΩ or higher
      TEXT IN ILLUSTRATION

      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *3 Front Seat Wire RH
      *4 No. 2 Floor Wire
      *a Front view of wire harness connector
      (to Front Seat Wire RH)

    NG → REPLACE NO. 2 FLOOR WIRE 

    OK → REPLACE FRONT SEAT WIRE RH 

  14. CHECK NO. 2 FLOOR WIRE (SHORT TO GROUND) 
    1. Disconnect the front seat wire RH connector from the No. 2 floor wire.
      Fig 8: Checking No. 2 Floor Wire For Short To Ground
      GTY338973Courtesy 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
      SW1-1 (FSR+) - Body ground Always 1 MΩ or higher
      SW1-4 (FSR-) - Body ground Always 1 MΩ or higher
      TEXT IN ILLUSTRATION

      *1 Occupant Detection ECU
      *2 Airbag ECU Assembly
      *3 Front Seat Wire RH
      *4 No. 2 Floor Wire
      *a Front view of wire harness connector
      (to Front Seat Wire RH)

    NG → REPLACE NO. 2 FLOOR WIRE 

    OK → REPLACE FRONT SEAT WIRE RH 

  15. USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING 
  16. REPLACE AIRBAG ECU ASSEMBLY. Refer to  REMOVAL 
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