Diagnostic Procedure for Subaru Select Monitor Communication: Inspection

Communication error with auto headlight beam leveler control module

Detecting condition: 

• Defective harness connector
• Power supply circuit malfunction
• Defective auto headlight beam leveler control module
• Defective CAN communication circuit
• Defective Subaru Select Monitor

Trouble symptom: 

Communication is impossible between auto headlight beam leveler control module and Subaru Select Monitor.

Wiring diagram: 

• Headlight beam leveler system Ref. to WIRING SYSTEM>HEADLIGHT BEAM LEVELER SYSTEM>WIRING DIAGRAM .
• CAN communication system Ref. to WIRING SYSTEM>CAN COMMUNICATION SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK FUSE  .

   Check the fuse. Ref. to WIRING SYSTEM>HEADLIGHT BEAM LEVELER SYSTEM>WIRING DIAGRAM .

   Is the check result OK?

   Yes  : GO TO  2.

   No  : Replace the fuse. If the replaced fuse has blown out immediately, repair the short circuit to ground in harness between battery and auto headlight beam leveler control module.

2. CHECK HARNESS (POWER SUPPLY CIRCUIT)  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from the auto headlight beam leveler control module.
   3. Turn the ignition switch to ON.
   4. Using a tester, measure the voltage between auto headlight beam leveler control module connector and chassis ground.

      Connector & terminal 

      (B78) No. 1 (+) - Chassis ground (-):

      (B78) No. 3 (+) - Chassis ground (-):

   Is the voltage 8 - 16 V?

   Yes  : GO TO  3.

   No  : Repair the open circuit in the harness between auto headlight beam leveler control module connector and fuse.

3. CHECK HARNESS (OPEN CIRCUIT)  .
   1. Turn the ignition switch to OFF.
   2. Using a tester, measure the resistance between the auto headlight beam leveler control module connector and chassis ground.

      Connector & terminal 

      (B78) No. 2 - Chassis ground:

   Is the resistance less than 1 Ω?

   Yes  : GO TO  4.

   No  : Repair the open circuit of harness between auto headlight beam leveler control module connector and chassis ground.

4. CHECK LAN SYSTEM  .

   Inspect LAN system. Ref. to LAN SYSTEM (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

   Is the check result OK?

   Yes  : GO TO  5.

   No  : Perform the inspection according to the diagnosis for LAN system. Ref. to LAN SYSTEM (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

5. CHECK SUBARU SELECT MONITOR  .
   1. Connect the Subaru Select Monitor to another vehicle.
   2. Check whether the communication for initializing can be executed normally.

   Is communication normal?

   Yes  : GO TO  6.

   No  : Repair or replace the Subaru Select Monitor.

6. CHECK AUTO HEADLIGHT BEAM LEVELER CONTROL MODULE  .
   1. Turn the ignition switch to OFF.
   2. Connect the auto headlight beam leveler control module connector.
   3. Turn the ignition switch to ON.
   4. Communicate with [Headlight/Foglight] using the Subaru Select Monitor.

   Is communication possible?

   Yes  : The circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again.

   NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.

   No  : Replace the auto headlight beam leveler control module. Ref. to LIGHTING SYSTEM>AUTO HEADLIGHT BEAM LEVELER CONTROL MODULE .