DTC B1409 SCU Communication

DTC detecting condition:

Communication failure between body integrated unit and security control module

CAUTION: When the body integrated unit is replaced, registration of the immobilizer system is required. For details, refer to the "REGISTRATION MANUAL FOR IMMOBILIZER" provided as a separate volume. Contact an Authorized Subaru Dealership.

Wiring diagram:

Immobilizer system Ref. to WIRING SYSTEM>Immobilizer System>WIRING DIAGRAM

Courtesy of SUBARU OF AMERICA, INC.

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.
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.
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.
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.
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.
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.
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
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
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. Ref. to IMMOBILIZER (DIAGNOSTICS)>Clear Memory Mode
4. Read the DTC of the body integrated unit. Ref. to IMMOBILIZER (DIAGNOSTICS)>Read Diagnostic Trouble Code (DTC)
Is DTC B1409 displayed?

Yes: Replace the body integrated unit. Ref. 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. Contact an Authorized Subaru Dealership.