DTC B177F: Front Left Occupant Detection Sensor

Diagnosis start condition: 

When ignition voltage is 10 - 16 V.

DTC detecting condition: 

Occupant detection sensor malfunction

Wiring diagram: 

Occupant detection system Ref. to WIRING SYSTEM>OCCUPANT DETECTION SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK DTC. 

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

   Is any of DTC B1771, B1788, B178A or B1795 displayed? (Current malfunction)

   Yes  : Perform the diagnosis for the displayed DTC B1771, 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, disconnect the battery ground terminal, and wait 60 seconds or more. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
   2. Disconnect the connector (AB69) from occupant detection control module.
   3. Disconnect connector (AB70) from the load sensor FL.
   4. Using a tester, measure the resistance between occupant detection control module connector and load sensor FL connector.
      CAUTION: Connect the terminal in test harness BC to connector (AB69) and connector (AB70) terminals, and apply the tester to test harness BC. Two sets of test harness BC are required.

      Connector and terminal 

      (AB69) No. 1 - (AB70) No. 3:

      (AB69) No. 7 - (AB70) No. 2:

      (AB69) No. 11 - (AB70) 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 and terminal 

   (AB69) No. 1 - All terminals other than (AB69) No. 1:

   (AB69) No. 7 - All terminals other than (AB69) No. 7:

   (AB69) No. 11 - All terminals other than (AB69) No. 11:

   (AB69) No. 1 - Chassis ground:

   (AB69) No. 7 - Chassis ground:

   (AB69) No. 11 - 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. Connect the battery ground terminal and turn the ignition switch to ON. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
   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.

      Connector and terminal 

      (AB69) No. 1 (+) - Chassis ground (-):

      (AB69) No. 7 (+) - Chassis ground (-):

      (AB69) No. 11 (+) - 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, disconnect the battery ground terminal, and wait 60 seconds or more. Ref. to REPAIR CONTENTS>NOTE>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 B177F displayed? (Current malfunction)

   Yes  : Replace the cushion frame assembly. Ref. to SEATS>Front Seat>DISASSEMBLY>POWER SEATS (TYPE WITH VENTILATION) .

   No  : Finish the diagnosis.