DTC B1781: Rear Left Occupant Detection Sensor

Diagnosis start condition: 

When the ignition voltage is 10 - 16 V.

DTC detecting condition: 

Occupant detection sensor malfunction

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 B1788, B178A or B1795 displayed? (Current malfunction)

   Yes  : Perform the diagnosis for the displayed DTC B1788, B178A or B1795. Ref. to OCCUPANT DETECTION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)>LIST .

   No  : Go to  2.

2. 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 (AB69) from occupant detection control module.
   3. Disconnect connector (AB71) from the load sensor RL.
   4. Using a tester, measure the resistance between occupant detection control module connector and load sensor RL connector.
      CAUTION: Connect the terminal in test harness BC to connector (AB69) and connector (AB71) terminals, and apply the tester to test harness BC. Two sets of test harness BC are required.

      Connector & terminal 

      (AB69) No. 3 - (AB71) No. 3:

      (AB69) No. 9 - (AB71) No. 2:

      (AB69) No. 5 - (AB71) No. 1:

   Is the resistance less than 10 Ω?

   Yes  : Go to  3.

   No  : Replace the seat harness.

3. 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 (AB69) terminal, and apply the tester to test harness BC. Two sets of test harness BC are required.

   Connector & terminal 

   (AB69) No. 3 - All terminals other than (AB69) No. 3:

   (AB69) No. 9 - All terminals other than (AB69) No. 9:

   (AB69) No. 5 - All terminals other than (AB69) No. 5:

   (AB69) No. 3 - Chassis ground:

   (AB69) No. 9 - Chassis ground:

   (AB69) No. 5 - Chassis ground:

   Is the resistance 1 MΩ or more?

   Yes  : Go to  4.

   No  : Replace the seat harness.

4. 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 (AB69) terminal, and apply the tester to test harness BC. Two sets of test harness BC are required.

      Connector & terminal 

      (AB69) No. 3 (+) - Chassis ground (-):

      (AB69) No. 9 (+) - Chassis ground (-):

      (AB69) No. 5 (+) - Chassis ground (-):

   Is the voltage less than 1 V?

   Yes  : Go to  5.

   No  : Replace the seat harness.

5. 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 load sensor connector.
   3. Disconnect the test harness BC, and connect all the connectors.
   4. Read the DTC of [Occupant Detection] using the Subaru Select Monitor. Ref. to OCCUPANT DETECTION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

   Is DTC B1781 displayed? (Current malfunction)

   Yes  : Replace the cushion frame assembly. Ref. to SEATS>FRONT SEAT>DISASSEMBLY>PASSENGER'S SEAT .

   No  : Finish the diagnosis.