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COMMUNICATION WITH [Occupant Detection] IS IMPOSSIBLE

WARNING: This page is about a different car, the 2021 Subaru Ascent. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: The occupant detection system communicates with the Subaru Select Monitor via the airbag control module. Detecting condition:

Defective harness connector between airbag control module and occupant detection control module

Trouble symptom: 

Communication is impossible between the airbag control module and the occupant detection control module.

CAUTION: Before performing diagnosis, refer to "CAUTION" in "General Description". Ref. to AIRBAG (DIAGNOSTICS)>General Description>CAUTION .
NOTE: Before starting work, prepare two sets of TEST HARNESS BC (98299FL030).

Wiring diagram: 

Occupant detection system Ref. to WIRING SYSTEM>Occupant Detection System>WIRING DIAGRAM .

G13872849Courtesy of SUBARU OF AMERICA, INC.
  1. CHECK SUBARU SELECT MONITOR COMMUNICATION  .
    1. Turn the ignition switch to ON.
    2. Using the Subaru Select Monitor, check whether the communication with [Airbag] can be executed normally.

    Is communication with [Airbag] possible?

    Yes  : Go to  5.

    No  : Go to  2.

  2. CHECK SUBARU SELECT MONITOR COMMUNICATION  .

    Using the Subaru Select Monitor, check whether the communication with [Body Control] can be executed normally.

    Is communication with [Body Control] possible?

    Yes  : Refer to AIRBAG (DIAGNOSTICS). Ref. to AIRBAG (DIAGNOSTICS)>DIAGNOSTIC PROCEDURE FOR SUBARU SELECT MONITOR COMMUNICATION .

    No  : Go to  3.

  3. CHECK SUBARU SELECT MONITOR  .

    Connect the Subaru Select Monitor to another vehicle to check whether the communication can be executed normally.

    Does the Subaru Select Monitor communicate?

    Yes  : Go to  4.

    No  : Repair or replace the Subaru Select Monitor.

  4. CHECK HARNESS BETWEEN DATA LINK CONNECTOR AND BODY INTEGRATED UNIT  .

    Check for malfunction in harness between data link connector and body integrated unit on vehicle to be diagnosed.

    Is the check result OK?

    Yes  : Replace the body integrated unit. Ref. to SECURITY AND LOCKS>BODY INTEGRATED UNIT .

    No  : Repair or replace the faulty harness.

  5. CHECK HARNESS IN OCCUPANT DETECTION CONTROL MODULE (OPEN CIRCUIT IN IGNITION POWER SUPPLY)  .
    1. Turn the ignition switch to OFF, and wait for 60 seconds or more after disconnecting the ground terminal from the battery sensor. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
    2. Disconnect the connector (AB61) of occupant detection control module.
    3. Install the ground terminal to the battery sensor and turn the ignition switch to ON. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
    4. Using a tester, measure the voltage between occupant detection control module connector and chassis ground.
    CAUTION: Connect the terminal in test harness BC to connector (AB61) terminal, and apply the tester to test harness BC.

    Connector & terminal 

    (AB61) No. 7 (+) - Chassis ground (-):

    Is the voltage 11 V or more?

    Yes  : Go to  7.

    No  : Go to  6.

  6. CHECK HARNESS IN OCCUPANT DETECTION CONTROL MODULE (OPEN CIRCUIT IN IGNITION POWER SUPPLY)  .
    1. Turn the ignition switch to OFF, and wait for 60 seconds or more after disconnecting the ground terminal from the battery sensor. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
    2. Disconnect the connector (AB59) of seat harness.
    3. Connect the connector (1AB) in the test harness AB to the connector (AB53).
    4. Install the ground terminal to the battery sensor and turn the ignition switch to ON. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
    5. Using a tester, measure the voltage between connector (2AB) in test harness AB and chassis ground.

      Connector & terminal 

      (2AB) No. 3 (+) - Chassis ground (-):

    Is the voltage 11 V or more?

    Yes  : Replace the seat harness.

    No  : Check rear harness, bulkhead wiring harness, instrument panel wiring harness in this order, and replace the faulty harness.

  7. CHECK HARNESS IN OCCUPANT DETECTION CONTROL MODULE (SHORT CIRCUIT IN IGNITION POWER SUPPLY)  .
    1. Turn the ignition switch to OFF, and wait for 60 seconds or more after disconnecting the ground terminal from the battery sensor. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
    2. Using a tester, measure the resistance between occupant detection control module connectors.
      CAUTION: Connect the terminal in test harness BC to connector (AB61) terminal, and apply the tester to test harness BC. Two sets of test harness BC are required.

      Connector & terminal 

      (AB61) No. 7 - (AB61) No. 1 - 12 (except for No. 7):

    Is the resistance 1 MΩ or more?

    Yes  : Go to  9.

    No  : Go to  8.

  8. CHECK HARNESS IN OCCUPANT DETECTION CONTROL MODULE (SHORT CIRCUIT IN IGNITION POWER SUPPLY)  .
    1. Disconnect the connector (AB59) of seat harness.
    2. Connect the connector (1AB) in the test harness AB to the connector (AB53).
    3. Using a tester, measure the resistance between terminals in test harness AB connector (2AB).

      Connector & terminal 

      (2AB) No. 3 - (2AB) No. 1 - 6 (except for No. 3):

    Is the resistance 1 MΩ or more?

    Yes  : Replace the seat harness.

    No  : Check rear harness, bulkhead wiring harness, instrument panel wiring harness in this order, and replace the faulty harness.

  9. CHECK HARNESS IN OCCUPANT DETECTION CONTROL MODULE (OPEN CIRCUIT IN GROUND)  .
    1. Turn the ignition switch to OFF, and wait for 60 seconds or more after disconnecting the ground terminal from the battery sensor. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
    2. Disconnect the connectors (AB6, AB17, AB18) from airbag control module.
    3. Connect the connector (1BD) in the test harness BD to the connectors (AB6, AB17, AB18).
    4. Using a tester, measure the resistance in harness between occupant detection control module connector and connector (4BD) in test harness BD.
      CAUTION: Connect the terminal in test harness BC to connector (AB61) terminal, and apply the tester to test harness BC.

      Connector & terminal 

    (AB61) No. 2 - (4BD) No. 2:

    (AB61) No. 3 - (4BD) No. 7:

    Is the resistance less than 10 Ω?

    Yes  : Go to  11.

    No  : Go to  10.

  10. CHECK HARNESS IN OCCUPANT DETECTION CONTROL MODULE (OPEN CIRCUIT IN GROUND)  .
    1. Disconnect the connector (AB59) of seat harness.
    2. Connect the connector (1AB) in the test harness AB to the connector (AB53).
    3. Using a tester, measure the resistance in harness between connector (2AB) in the test harness AB and connector (4BD) in the test harness BD.

      Connector & terminal 

      (2AB) No. 1 - (4BD) No. 2:

      (2AB) No. 2 - (4BD) No. 7:

    Is the resistance less than 10 Ω?

    Yes  : Replace the seat harness.

    No  : Check rear harness, bulkhead wiring harness, instrument panel wiring harness in this order, and replace the faulty harness.

  11. CHECK HARNESS IN OCCUPANT DETECTION CONTROL MODULE (SHORT CIRCUIT IN GROUND)  .

    Using a tester, measure the resistance between connectors in test harness BD.

    Connector & terminal 

    (4BD) No. 2 - All terminals in test harness BD (except for (4BD) No. 2):

    (4BD) No. 7 - All terminals in test harness BD (except for (4BD) No. 7):

    Is the resistance 1 MΩ or more?

    Yes  : Go to  13.

    No  : Go to  12.

  12. CHECK HARNESS IN OCCUPANT DETECTION CONTROL MODULE (SHORT CIRCUIT IN GROUND)  .
    1. Disconnect the connector (AB59) of seat harness.
    2. Using a tester, measure the resistance between connectors in test harness BD.

      Connector & terminal 

      (4BD) No. 2 - All terminals in test harness BD (except for (4BD) No. 2):

      (4BD) No. 7 - All terminals in test harness BD (except for (4BD) No. 7):

    Is the resistance 1 MΩ or more?

    Yes  : Replace the seat harness.

    No  : Check rear harness, bulkhead wiring harness, instrument panel wiring harness in this order, and replace the faulty harness.

  13. CHECK FOR POOR CONTACT  .

    Check for poor contact of connector of occupant detection system.

    Is the check result OK?

    Yes  : Replace the occupant detection control module. Ref. to SEATS>Front Seat>DISASSEMBLY>POWER SEATS (TYPE WITH VENTILATION) .

    No  : Repair or replace the connector. (Replace the harness without repairing the airbag system connector.)

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