DTC B1409: SCU Communication

DTC detecting condition: 

Communication failure between body integrated unit and security control module

Wiring diagram: 

Immobilizer system Refer to WIRING SYSTEM>IMMOBILIZER SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK BODY INTEGRATED UNIT POWER SUPPLY CIRCUIT. 
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from body integrated unit.
   3. Measure the voltage between the body integrated unit connector terminal and chassis ground.

      Connector & terminal 

      (i84) No. 6 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes:  Go to  2.

   No:  Check the harness for open or short circuit between body integrated unit and fuse.

2. CHECK BODY INTEGRATED UNIT POWER SUPPLY CIRCUIT. 
   1. Turn the ignition switch to ON.
   2. Measure the voltage between the body integrated unit connector terminal and chassis ground.

      Connector & terminal 

      (B281) No. 3 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes:  Go to  3.

   No:  Check the harness for open or short circuit between the body integrated unit and ignition switch.

3. CHECK BODY INTEGRATED UNIT GROUND CIRCUIT (OPEN CIRCUIT). 
   1. Turn the ignition switch to OFF.
   2. Measure the resistance between the body integrated unit connector terminal and chassis ground.

      Connector & terminal 

      (B280) No. 1 - Chassis ground:

      (i84) No. 1 - Chassis ground:

   Is the resistance less than 10 Ω?

   Yes:  Go to  4.

   No:  Repair the open circuit of the body integrated unit ground circuit.

4. CHECK SECURITY CONTROL MODULE POWER SUPPLY CIRCUIT. 
   1. Disconnect the connector from the security control module.
   2. Measure the power supply between security control module connector terminal and chassis ground.

      Connector & terminal 

      (B559) No. 1 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes:  Go to  5.

   No:  Check for an open or short circuit in the harness between security control module and fuse.

5. CHECK SECURITY CONTROL MODULE GROUND CIRCUIT (OPEN). 

   Measure the resistance between security control module connector terminal and chassis ground.

   Connector & terminal 

   (B559) No. 5 - Chassis ground:

   Is the resistance less than 10 Ω?

   Yes:  Go to  6.

   No:  Repair the open circuit of the security control module ground circuit.

6. CHECK HARNESS (OPEN CIRCUIT) BETWEEN BODY INTEGRATED UNIT AND SECURITY CONTROL MODULE. 

   Measure the resistance between the body integrated unit connector terminal and security control module connector terminal.

   Connector & terminal 

   (B280) No. 21 - (B559) No. 3:

   Is the resistance less than 10 Ω?

   Yes:  Go to  7.

   No:  Repair the harness between body integrated unit and security control module.

7. CHECK COMMUNICATION LINE HARNESS (SHORT CIRCUIT TO POWER SUPPLY). 
   1. Turn the ignition switch to ON.
   2. Measure the voltage between security control module connector terminal and chassis ground.

      Connector & terminal 

      (B559) No. 3 (+) - Chassis ground (-):

   Is the voltage 6 V or more?

   Yes:  Repair the harness between body integrated unit and security control module.

   No:  Go to  8.

8. CHECK COMMUNICATION CIRCUIT HARNESS (SHORT CIRCUIT TO GROUND). 
   1. Turn the ignition switch to OFF.
   2. Measure the resistance between security control module connector terminal and chassis ground.

      Connector & terminal 

      (B559) No. 3 - Chassis ground:

   Is the resistance less than 10 Ω?

   Yes:  Repair the harness between body integrated unit and ECM.

   No:  Go to  9.

9. CHECK SECURITY CONTROL MODULE. 
   1. Replace the security control module. (Do not perform security control module registration.)
   2. Turn the ignition switch to ON.
   3. Perform the Clear Memory Mode. Refer to IMMOBILIZER (DIAGNOSTICS)>CLEAR MEMORY MODE .
   4. Read the DTC of the body integrated unit. Refer to IMMOBILIZER (DIAGNOSTICS)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

   Is DTC B1409 displayed?

   Yes:  Replace the body integrated unit. Refer to SECURITY AND LOCKS>BODY INTEGRATED UNIT .

   No:  Security control module was defective. Perform security control module registration. Refer to the "REGISTRATION MANUAL FOR IMMOBILIZER" provided as a separate volume.