OCCUPANT CLASSIFICATION SYSTEM, Diagnostic DTC:B1790

DTC Code DTC Name
B1790 Center Airbag Sensor Assembly Communication Circuit Malfunction

DESCRIPTION

The airbag sensor assembly communication circuit consists of the occupant detection ECU and airbag sensor assembly.

DTC B1790 is stored when a malfunction is detected in the airbag sensor assembly communication circuit.

DTC No. DTC Detection Condition Trouble Area
B1790

  • The occupant detection ECU receives a line short circuit signal, an open circuit signal, a short circuit to ground signal or a short circuit to B+ signal in the airbag sensor assembly communication circuit.

  • Occupant detection ECU malfunction

  • Airbag sensor assembly malfunction

  • No. 2 floor wire

  • Front seat wire RH

  • Occupant detection ECU

  • Airbag sensor assembly

Tech Tips

When DTC B1650/32 is detected as a result of troubleshooting for the airbag system, check the DTCs stored in the occupant detection ECU. When DTC B1790 is output, perform troubleshooting for the DTC.

WIRING DIAGRAM

A01HV07E05

INSPECTION PROCEDURE

Note

After turning the power switch off, waiting time may be required before disconnecting the cable from the negative (-) auxiliary battery terminal. Therefore, make sure to read the disconnecting the cable from the negative (-) auxiliary battery terminal notices before proceeding with work Click here.

Tech Tips


  • If troubleshooting (wire harness inspection) is difficult to perform, remove the front passenger seat installation bolts to see under the seat cushion.

  • In the above case, lift and hold the seat so that it does not fall down. Hold the seat only as necessary because holding the seat for a long period of time may cause seat rail deformation.

PROCEDURE


  1. CHECK CONNECTORS


    1. Turn the power switch off.

    2. Disconnect the cable from the negative (-) auxiliary battery terminal.

      CAUTION:

      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 sensor 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.

      Tech Tips

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

    4. Disconnect the connectors from the airbag sensor 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

  2. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT TO B+)


    1. A01HW21E03
      Text in Illustration
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *a

      Front view of wire harness connector

      (to Occupant Detection ECU)

      Connect the connectors that link the No. 2 floor wire and front seat wire RH.

    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
      d11-7 (FSR+) - Body ground Power switch on (IG) Below 1 V
      d11-4 (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.

      CAUTION:

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


    NG

    CHECK NO. 2 FLOOR WIRE (SHORT TO B+) Click here

    OK

  3. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (OPEN)


    1. A01HU2EE02
      Text in Illustration
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Service Wire
      *a

      Front view of wire harness connector

      (to Airbag Sensor Assembly)
      *b

      Front view of wire harness connector

      (to Occupant Detection ECU)

      Using a service wire, connect terminals 16 (FSR+) and 24 (FSR-) of connector B.

      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
      d11-7 (FSR+) - d11-4 (FSR-) Always Below 1 Ω

    NG

    CHECK NO. 2 FLOOR WIRE (OPEN) Click here

    OK

  4. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT)


    1. A01HW21E03
      Text in Illustration
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *a

      Front view of wire harness connector

      (to Occupant Detection ECU)

      Disconnect the service wire from connector B.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      d11-7 (FSR+) - d11-4 (FSR-) Always 1 MΩ or higher

    NG

    CHECK NO. 2 FLOOR WIRE (SHORT) Click here

    OK

  5. CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT (SHORT TO GROUND)


    1. A01HW21E03
      Text in Illustration
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *a

      Front view of wire harness connector

      (to Occupant Detection ECU)

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      d11-7 (FSR+) - Body ground Always 1 MΩ or higher
      d11-4 (FSR-) - Body ground Always 1 MΩ or higher

    NG

    CHECK NO. 2 FLOOR WIRE (SHORT TO GROUND) Click here

    OK

  6. CHECK DTC


    1. Connect the connectors to the occupant detection ECU and airbag sensor assembly.

    2. Connect the cable to the negative (-) auxiliary battery terminal.

    3. Clear the DTCs stored in the occupant detection ECU Click here.

    4. Clear the DTCs stored in the airbag sensor assembly Click here.

    5. Turn the power switch off.

    6. Turn the power switch on (IG).

    7. Check for DTCs Click here.

      OK
      DTC B1790 is not output.

      Tech Tips

      Codes other than DTC B1790 may be output at this time, but they are not related to this check.

    8. Turn the power switch off.


    NG

    CHECK OCCUPANT DETECTION ECU Click here

    OK

    USE SIMULATION METHOD TO CHECK Click here

  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 Click here.

      Tech Tips

      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 Click here.

    5. Clear the DTCs stored in the airbag sensor assembly Click here.

    6. Turn the power switch off.

    7. Turn the power switch on (IG).

    8. Check for DTCs Click here.

      OK
      DTC B1790 is not output.

      Tech Tips

      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. Restore the occupant detection ECU that was installed for testing to its original location Click here.


    NG

    REPLACE AIRBAG SENSOR ASSEMBLY Click here

    OK

  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 Click here.

    3. Connect the cable to the negative (-) auxiliary battery terminal.


    NEXT

  9. PERFORM ZERO POINT CALIBRATION AND SENSITIVITY CHECK


    1. Using the Techstream, perform Zero Point Calibration and Sensitivity Check Click here.


    NEXT

    END

  10. CHECK NO. 2 FLOOR WIRE (SHORT TO B+)


    1. A01HT98E02
      Text in Illustration
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Front Seat Wire RH
      *4 No. 2 Floor Wire
      *a

      Front view of wire harness connector

      (to Front Seat Wire RH)

      Disconnect the front seat wire RH connector from the No. 2 floor wire.

    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
      Od2-1 (FSR+) - Body ground Power switch on (IG) Below 1 V
      Od2-5 (FSR-) - Body ground Power switch on (IG) Below 1 V

    NG

    REPLACE NO. 2 FLOOR WIRE

    OK

    REPLACE FRONT SEAT WIRE RH

  11. CHECK NO. 2 FLOOR WIRE (OPEN)


    1. A01HVLXE02
      Text in Illustration
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Front Seat Wire RH
      *4 No. 2 Floor Wire
      *5 Service Wire
      *a

      Front view of wire harness connector

      (to Airbag Sensor Assembly)
      *b

      Front view of wire harness connector

      (to Front Seat Wire RH)

      Disconnect the front seat wire RH connector from the No. 2 floor wire.

      Tech Tips

      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
      Od2-1 (FSR+) - Od2-5 (FSR-) Always Below 1 Ω

    3. Disconnect the service wire from connector B.


    NG

    REPLACE NO. 2 FLOOR WIRE

    OK

    REPLACE FRONT SEAT WIRE RH

  12. CHECK NO. 2 FLOOR WIRE (SHORT)


    1. A01HT98E02
      Text in Illustration
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Front Seat Wire RH
      *4 No. 2 Floor Wire
      *a

      Front view of wire harness connector

      (to Front Seat Wire RH)

      Disconnect the front seat wire RH connector from the No. 2 floor wire.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      Od2-1 (FSR+) - Od2-5 (FSR-) Always 1 MΩ or higher

    NG

    REPLACE NO. 2 FLOOR WIRE

    OK

    REPLACE FRONT SEAT WIRE RH

  13. CHECK NO. 2 FLOOR WIRE (SHORT TO GROUND)


    1. A01HT98E02
      Text in Illustration
      *1 Occupant Detection ECU
      *2 Airbag Sensor Assembly
      *3 Front Seat Wire RH
      *4 No. 2 Floor Wire
      *a

      Front view of wire harness connector

      (to Front Seat Wire RH)

      Disconnect the front seat wire RH connector from the No. 2 floor wire.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      Od2-1 (FSR+) - Body ground Always 1 MΩ or higher
      Od2-5 (FSR-) - Body ground Always 1 MΩ or higher

    NG

    REPLACE NO. 2 FLOOR WIRE

    OK

    REPLACE FRONT SEAT WIRE RH