LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Lexus >> 2021 >> NX 300 Base, AWD >> Repair and Diagnosis (Single Page) >> Restraints >> Air Bag, SRS >> Occupant Classification System - Diagnostic Codes & Symptom Tests >> Occupant Classification System >> DTC B1780: Front Occupant Classification Sensor LH Circuit Malfunction [10/2014 - ] >> Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC B1780: Front Occupant Classification Sensor LH Circuit Malfunction [10/2014 - ]: Procedure

  1. CHECK DTC 
    1. Turn the engine switch on (IG), and wait for at least 60 seconds.
    2. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Clear DTCs 

      HINT: 

      • First clear the DTCs stored in the occupant detection ECU, and then clear the DTCs stored in the airbag ECU assembly.
      • Use the Techstream to clear the DTCs of the occupant detection ECU, otherwise the DTCs cannot be cleared.
    3. Turn the engine switch off.
    4. Turn the engine switch on (IG), and wait for at least 60 seconds.
    5. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Trouble Codes 

      Result

      Proceed to
      DTC B1780 is not output
      DTC B1780 is output

      HINT: 

      DTCs other than DTC B1780 may be output at this time, but they are not related to this check.

    Result: 

    DTC B1780 is not output 

    USE SIMULATION METHOD TO CHECK. Refer to  DIAGNOSIS SYSTEM [10/2014 - ] 

    Result: 

    DTC B1780 is output 

    See step  2

  2. CHECK CONNECTION OF CONNECTORS 
    1. Turn the engine switch off.
    2. Disconnect the cable from the negative (-) battery terminal, and wait for at least 90 seconds.
    3. Check that the connectors are properly connected to the occupant detection ECU and front occupant classification sensor LH.

      Result

      Proceed to
      Connectors are properly connected
      Connectors are not properly connected

    Result: 

    Connectors are not properly connected 

    CONNECT CONNECTORS 

    Result: 

    Connectors are properly connected 

    See step  3

  3. CHECK CONNECTOR 
    1. Disconnect the connectors from the occupant detection ECU and front occupant classification sensor LH.
      GTY366093Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Front Occupant Classification Sensor LH
      *2 Occupant Detection ECU
      *3 Front Seat Wire RH
    2. Check that the connectors (on the occupant detection ECU side and front occupant classification sensor LH side) are not damaged.

      Result

      Proceed to
      Connectors are not deformed or damaged
      Connectors are deformed or damaged

    Result: 

    Connectors are deformed or damaged 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    Connectors are not deformed or damaged 

    See step  4

  4. CHECK FRONT SEAT WIRE RH 
    1. Connect the cable to the negative (-) battery terminal, and wait for at least 2 seconds.
      GTY517527Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *1 Front Seat Wire RH
      *2 Front Occupant Classification Sensor LH
      *3 Occupant Detection ECU
      *4 Service Wire
      *5 Connector C
      *6 Connector B
      *a Front view of wire harness connector
      (to Front Occupant Classification Sensor LH)
      *b Front view of wire harness connector
      (to Occupant Detection ECU)
    2. Turn the engine switch on (IG).
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      f14-1 (SVC1) - Body ground Engine switch on (IG) Below 1 V
      f14-3 (SIG1) - Body ground
      f14-5 (SGD1) - Body ground
    4. Turn the engine switch off.
    5. Disconnect the cable from the negative (-) battery terminal, and wait for at least 90 seconds.
    6. Using service wires, connect terminals 1 (SVC) and 3 (SGD), and terminals 2 (SIG) and 3 (SGD) of connector C.
      NOTE:

      Do not forcibly insert the service wires into the terminals of the connector.

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

      Standard Resistance

      Tester Connection Condition Specified Condition
      f14-1 (SVC1) - f14-5 (SGD1) Always Below 1 Ω
      f14-3 (SIG1) - f14-5 (SGD1)
    8. Disconnect the service wires from connector C.
    9. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      f14-1 (SVC1) - f14-5 (SGD1) Always 1 MΩ or higher
      f14-3 (SIG1) - f14-5 (SGD1)
      f14-1 (SVC1) - f14-3 (SIG1)
      f14-1 (SVC1) - Body ground
      f14-3 (SIG1) - Body ground
      f14-5 (SGD1) - Body ground

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE FRONT SEAT WIRE RH 

    Result: 

    OK 

    See step  5

  5. CHECK DTC 
    1. Connect the connectors to the occupant detection ECU and front occupant classification sensor LH.
    2. Connect the cable to the negative (-) battery terminal, and wait for at least 2 seconds.
    3. Turn the engine switch on (IG), and wait for at least 60 seconds.
    4. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Clear DTCs 

      HINT: 

      • First clear the DTCs stored in the occupant detection ECU, and then clear the DTCs stored in the airbag ECU assembly.
      • Use the Techstream to clear the DTCs of the occupant detection ECU, otherwise the DTCs cannot be cleared.
    5. Turn the engine switch off.
    6. Turn the engine switch on (IG), and wait for at least 60 seconds.
    7. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Trouble Codes 

      Result

      Proceed to
      DTC B1780 is not output
      DTC B1780 is output

      HINT: 

      DTCs other than DTC B1780 may be output at this time, but they are not related to this check.

    Result: 

    DTC B1780 is not output 

    USE SIMULATION METHOD TO CHECK. Refer to  DIAGNOSIS SYSTEM [10/2014 - ] 

    Result: 

    DTC B1780 is output 

    See step  6

  6. REPLACE OCCUPANT DETECTION ECU 
    1. Turn the engine switch off.
    2. Disconnect the cable from the negative (-) battery terminal, and wait for at least 90 seconds.
    3. Replace the occupant detection ECU.

      Refer to REMOVAL [10/2014 - 05/2019] , or refer to REMOVAL [05/2019 - ]

      Result

      Proceed to
      "Zero Point Calibration is complete." is displayed

      HINT: 

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

    Result: 

    "Zero Point Calibration is complete." is displayed 

    See step  7

  7. PERFORM ZERO POINT CALIBRATION 
    1. Connect the cable to the negative (-) battery terminal, and wait for at least 2 seconds.
    2. Turn the engine switch on (IG)
    3. Perform the zero point calibration.

      Refer to INITIALIZATION [10/2014 - ]

      Result

      Proceed to
      "Zero Point Calibration is complete." is displayed
      "Zero Point Calibration is complete." is not displayed

    Result: 

    "Zero Point Calibration is complete." is not displayed 

    See step  10

    Result: 

    "Zero Point Calibration is complete." is displayed 

    See step  8

  8. PERFORM SENSITIVITY CHECK 
    1. Perform the sensitivity check.

      Refer to INITIALIZATION [10/2014 - ]

      Standard

      27 to 33 kg (59.5 to 72.8 lb)

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  10

    Result: 

    OK 

    See step  9

  9. CHECK DTC 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Clear DTCs 

      HINT: 

      • First clear the DTCs stored in the occupant detection ECU, and then clear the DTCs stored in the airbag ECU assembly.
      • Use the Techstream to clear the DTCs of the occupant detection ECU, otherwise the DTCs cannot be cleared.
    2. Turn the engine switch off.
    3. Turn the engine switch on (IG), and wait for at least 60 seconds.
    4. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2014 - ]

      Body Electrical > Occupant Detection > Trouble Codes 

      Result

      Proceed to
      DTC B1780 is not output
      DTC B1780 is output

      HINT: 

      DTCs other than DTC B1780 may be output at this time, but they are not related to this check.

    Result: 

    DTC B1780 is not output 

    END (OCCUPANT DETECTION ECU WAS DEFECTIVE) 

    Result: 

    DTC B1780 is output 

    See step  10

  10. REPLACE FRONT SEAT ADJUSTER ASSEMBLY RH (FRONT OCCUPANT CLASSIFICATION SENSOR LH) 
    1. Turn the engine switch off.
    2. Disconnect the cable from the negative (-) battery terminal, and wait for at least 90 seconds.
    3. Replace the front seat adjuster assembly RH.

      Refer to DISASSEMBLY [10/2014 - ]

      HINT: 

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

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  11

  11. PERFORM ZERO POINT CALIBRATION 
    1. Connect the cable to the negative (-) battery terminal, and wait for at least 2 seconds.
    2. Turn the engine switch on (IG).
    3. Perform the zero point calibration.

      Refer to INITIALIZATION [10/2014 - ]

      Result

      Proceed to
      "Zero Point Calibration is complete." is displayed

    Result: 

    "Zero Point Calibration is complete." is displayed 

    See step  12

  12. PERFORM SENSITIVITY CHECK 
    1. Perform the sensitivity check.

      Refer to INITIALIZATION [10/2014 - ]

      Standard

      27 to 33 kg (59.5 to 72.8 lb)

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    END (FRONT SEAT ADJUSTER ASSEMBLY RH [FRONT OCCUPANT CLASSIFICATION SENSOR LH] WAS DEFECTIVE) 

scientia non olet · About LEMON Manuals