DTC B1771: Buckle Switch

Diagnosis start condition: 

When the ignition voltage is 10 - 16 V.

DTC detecting condition: 

• Open circuit, ground short circuit or short circuit to power supply in buckle switch harness
• Buckle switch malfunction (Communication circuit failure)
• Occupant detection control module buckle communication circuit malfunction

Trouble symptom: 

Communication fails between occupant detection control module and buckle switch.

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 DTC  .
   1. Turn the ignition switch to ON.
   2. Read the DTC of [Occupant Detection] using the Subaru Select Monitor. Ref. to OCCUPANT DETECTION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

   Is any of DTC B177F, B1780, B1781, B1782, B1788, B178A or B1795 displayed? (Current malfunction)

   Yes  : Perform the diagnosis for the displayed DTC B177F, B1780, B1781, B1782, B1788, B178A or B1795.

   No  : Go to  2.

2. CHECK DTC  .

   Read the DTC of [Occupant Detection] using the Subaru Select Monitor. Ref. to OCCUPANT DETECTION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

   Is DTC B1655 displayed? (Current malfunction)

   Yes  : Go to  3.

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

3. 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. Disconnect the connector (AB61) from occupant detection control module.
   3. Disconnect the connector (AB60) from the passenger's buckle switch.
   4. Connect the connector (2D) in the test harness D to the connector (AB60).
   5. Using a tester, measure the resistance between occupant detection control module connector and connector (3D) in test harness D.
      CAUTION: Connect the terminal in test harness BC to connector (AB61) terminal, and apply the tester to test harness BC.

      Connector & terminal 

      (AB61) No. 5 - (3D) No. 5:

      (AB61) No. 9 - (3D) No. 6:

   Is the resistance less than 10 Ω?

   Yes  : Go to  4.

   No  : Replace the seat harness.

4. CHECK SEAT HARNESS (SHORTED BETWEEN LINES AND SHORTED TO GROUND)  .

   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 & terminal 

   (AB61) No. 5 - All terminals other than (AB61) No. 5:

   (AB61) No. 9 - All terminals other than (AB61) No. 9:

   (AB61) No. 5 - Chassis ground:

   (AB61) No. 9 - Chassis ground:

   Is the resistance 1 MΩ or more?

   Yes  : Go to  5.

   No  : Replace the seat harness.

5. CHECK SEAT HARNESS (BATTERY SHORT)  .
   1. 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.
   2. 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. 5 (+) - Chassis ground (-):

      (AB61) No. 9 (+) - Chassis ground (-):

   Is the voltage less than 1 V?

   Yes  : Go to  6.

   No  : Replace the seat harness.

6. CHECK 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. Check for poor contact in occupant detection control module connector and passenger's buckle switch connector.

   Is the check result OK?

   Yes  : Go to  7.

   No  : Repair or replace the poor contact part.

7. CHECK PASSENGER'S SEAT BUCKLE SWITCH  .
   1. Disconnect the test harness D and test harness BC.
   2. Connect the occupant detection control module connector.
   3. Connect the test harness AE and test harness connector Y to buckle switch connector (AB60).
   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.

   Does the airbag warning light illuminate for 6 seconds and go off?

   Yes  : Replace the buckle switch. Ref. to SEAT BELT SYSTEM>FRONT SEAT BELT>REMOVAL>SEAT BELT OUTER - FRONT .

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