DTC B1789: +B Power Supply

Diagnosis start condition: 

When the ignition voltage is 10 - 16 V.

DTC detecting condition: 

• Poor contact in harness between occupant detection control module and battery
• Battery malfunction
• Occupant detection control module malfunction

Trouble symptom: 

Occupant judgment of occupant detection control module stops.

Wiring diagram: 

Occupant detection system Ref. to WIRING SYSTEM (IMPREZA MODEL)>OCCUPANT DETECTION SYSTEM>WIRING DIAGRAM . Ref. to WIRING SYSTEM (CROSSTREK MODEL (EXCEPT FOR HEV))>OCCUPANT DETECTION SYSTEM>WIRING DIAGRAM . Ref. to WIRING SYSTEM (CROSSTREK MODEL (HEV))>OCCUPANT DETECTION SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK BATTERY  .

   Check the battery. Ref. to STARTING/CHARGING SYSTEMS (H4DO (EXCEPT FOR HEV))>BATTERY>INSPECTION . Ref. to STARTING/CHARGING SYSTEMS (H4DO(HEV))>BATTERY>INSPECTION .

   Is the check result OK?

   Yes:  Go to  2.

   No:  Charge or replace the battery.

2. CHECK FUSE  .

   Check the fuse of occupant detection control module.

   Is the fuse OK?

   Yes:  Go to  3.

   No:  Replace the fuse. If the replaced fuse blows out easily, repair or replace the short circuit in the harness between battery and occupant detection control module.

3. CHECK OCCUPANT DETECTION CONTROL MODULE CONNECTOR  .
   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>REPAIR CONTENTS>NOTE>BATTERY .
      NOTE: For the hybrid model, turn the ignition switch to OFF, and wait for 60 seconds or more after disconnecting the ground terminal from the battery.
   2. Confirm that the connector of the occupant detection control module (AB61) is securely connected.

   Is the connector of the occupant detection control module securely connected?

   Yes:  Go to  4.

   No:  Reconnect the connector of the occupant detection control module.

4. CHECK HARNESS (OPEN CIRCUIT BETWEEN BATTERY AND OCCUPANT DETECTION CONTROL MODULE)  .
   1. Disconnect the connector (AB61) of occupant detection control module.
   2. Install the ground terminal to the battery sensor and turn the ignition switch to ON. Ref. to REPAIR CONTENTS>REPAIR CONTENTS>NOTE>BATTERY .
      NOTE: For the hybrid model, connect the battery ground terminal and turn the ignition switch to ON.
   3. 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 and terminal 

      (AB61) No. 1 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes:  Go to  8.

   No:  Go to  5.

5. CHECK HARNESS (OPEN CIRCUIT BETWEEN BATTERY AND REAR HARNESS)  .
   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>REPAIR CONTENTS>NOTE>BATTERY .
      NOTE: For the hybrid model, turn the ignition switch to OFF, and wait for 60 seconds or more after disconnecting the ground terminal from the 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>REPAIR CONTENTS>NOTE>BATTERY .
      NOTE: For the hybrid model, connect the battery ground terminal and turn the ignition switch to ON.
   5. Using a tester, measure the voltage between connector (2AB) in test harness AB and chassis ground.

      Connector and terminal 

      (2AB) No. 6 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes:  Go to  6.

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

6. CHECK SEAT HARNESS (OPEN CIRCUIT)  .
   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>REPAIR CONTENTS>NOTE>BATTERY .
      NOTE: For the hybrid model, turn the ignition switch to OFF, and wait for 60 seconds or more after disconnecting the ground terminal from the battery.
   2. Connect the connector (1BB) in the test harness BB to the connector (AB59).
   3. Using a tester, measure the resistance between occupant detection control module connector and connector (2BB) in test harness BB.
      CAUTION: Connect the terminal in test harness BC to connector (AB61) terminal, and apply the tester to test harness BC.

      Connector and terminal 

      (AB61) No. 1 - (2BB) No. 6:

   Is the resistance less than 10 Ω?

   Yes:  Go to  7.

   No:  Replace the seat harness.

7. CHECK SEAT HARNESS (SHORT)  .

   Using a tester, measure the resistance between occupant detection control module connector and chassis ground, and between occupant detection control module connector terminals.

   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 and terminal 

   (AB61) No. 1 - Chassis ground:

   (AB61) No. 1 - All terminals other than (AB61) No. 1:

   Is the resistance 1 MΩ or more?

   Yes:  Go to  8.

   No:  Replace the seat harness.

8. CHECK HARNESS (OPEN CIRCUIT BETWEEN OCCUPANT DETECTION CONTROL MODULE AND 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>REPAIR CONTENTS>NOTE>BATTERY .
      NOTE: For the hybrid model, turn the ignition switch to OFF, and wait for 60 seconds or more after disconnecting the ground terminal from the battery.
   2. Connect all the connectors other than (AB61) of occupant detection control module.
   3. Using a tester, measure the resistance between occupant detection control module connector (AB61) and chassis ground.
      CAUTION: Connect the terminal in test harness BC to connector (AB61) terminal, and apply the tester to test harness BC.

      Connector and terminal 

      (AB61) No. 3 - Chassis ground:

   Is the resistance less than 10 Ω?

   Yes:  Go to  11.

   No:  Go to  9.

9. CHECK HARNESS (OPEN CIRCUIT BETWEEN REAR HARNESS AND 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 between connector (2AB) in test harness AB and chassis ground.

      Connector and terminal 

      (2AB) No. 2 - Chassis ground:

   Is the resistance less than 10 Ω?

   Yes:  Replace the seat harness.

   No:  Go to  10.

10. CHECK HARNESS (OPEN CIRCUIT BETWEEN AIRBAG CONTROL MODULE AND GROUND)  .
    1. Disconnect the connectors (AB6, AB17, AB18) from airbag control module.
    2. Connect the connector (1AG) in the test harness AG to the connectors (AB6, AB17, AB18).
    3. Using a tester, measure the resistance between connector (2AG) in test harness AG and chassis ground.

       Connector and terminal 

       (2AG) No. 4 - Chassis ground:

       (2AG) No. 3 - Chassis ground:

    Is the resistance less than 10 Ω?

    Yes:  Go to  11.

    No:  Check for poor contact in grounding point. If faulty, repair it.

11. CHECK POOR CONTACT OF CONNECTORS  .

    Check for poor contact in the connector of the occupant detection control module.

    Is there poor contact?

    Yes:  Repair or replace the connector. (Replace the harness without repairing the airbag system connector.)

    No:  Replace the occupant detection control module. Ref. to SEATS>FRONT SEAT>DISASSEMBLY>PASSENGER'S SEAT .