DTC B1921: Open In Rear P/T RH

Diagnosis start condition: 

When the ignition voltage is 10 - 16 V.

DTC detecting condition: 

• Rear pretensioner harness RH circuit is open.
• Rear seatbelt pretensioner RH is faulty.
• Airbag control module is faulty.

Wiring diagram: 

Airbag system Ref. to WIRING SYSTEM>AIRBAG SYSTEM>WIRING DIAGRAM

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK POOR CONTACT OF CONNECTORS  .

   Check for poor contact of the connectors between the airbag control module and Rear seatbelt pretensioner RH.

   Is there poor contact?

   Yes  : Replace the airbag rear harness along with body harness.

   No  : Go to  2.

2. CHECK AIRBAG REAR HARNESS (REAR PRETENSIONER HARNESS RH) (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>NOTE>BATTERY
   2. Disconnect the connector (AB93) from seat belt pretensioner RH.
   3. Disconnect the connector (AB95) from the lap seat belt pretensioner RH.
   4. Disconnect the connector (AB99) from Rear seatbelt pretensioner RH.
   5. Disconnect the connector (AB91) from curtain airbag module RH.
   6. Disconnect the connector (AB87) from side airbag module RH.
   7. Disconnect the connectors (AB41, AB42, AB43) from airbag control module.
   8. Using a probe, measure the resistance between the terminals of connector (AB99). Ref. to AIRBAG (DIAGNOSTICS)>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE PROBE 
      CAUTION:

      When measuring the resistance, make sure that the probe is inserted from the back side (harness side) of the connector. Also, do not insert the probe forcibly. 

      Connector & terminal 

      (AB99) No. 2 - (AB99) No. 3:

   Is the resistance less than 10 Ω?

   Yes  : Go to  3.

   No  : Replace the airbag rear harness along with body harness.

3. CHECK AIRBAG CONTROL MODULE  .
   1. Connect all the connectors other than (AB99) of Rear seatbelt pretensioner RH.
   2. Using a probe, short the terminals No. 2 and No. 3 of connector (AB99). Ref. to AIRBAG (DIAGNOSTICS)>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE PROBE 
      CAUTION:

      When shorting the terminals, make sure that the probe is inserted from the back side (harness side) of the connector. Also, do not insert the probe forcibly. 

      Connector & terminal 

      (AB99) No. 2 - (AB99) No. 3

   3. Install the ground terminal to the battery sensor and turn the ignition switch to ON. Ref. to REPAIR CONTENTS>NOTE>BATTERY
   4. Using the Subaru Select Monitor, perform the clear memory of [Airbag]. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY
   5. Execute the inspection mode. Ref. to AIRBAG (DIAGNOSTICS)>INSPECTION MODE 
   6. Read the DTC of [Airbag] using the Subaru Select Monitor. Ref. to AIRBAG (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) 

   Is DTC B1921 displayed? (Current code)

   Yes  : Replace the airbag control module. Ref. to AIRBAG SYSTEM>AIRBAG CONTROL MODULE>REMOVAL

   No  : Replace Rear seatbelt pretensioner RH. Ref. to SEAT BELT SYSTEM>REAR SEAT BELT