DTC U115B: Lost Communication With Restraints Control Module Local Bus

Diagnosis start condition: 

When ignition switch is ON.

DTC detecting condition: 

• Malfunction of CAN communication harness between airbag control module and DCM.
• Defective airbag control module.
• Defective DCM.

Trouble symptom: 

• Impossible to send ACN data.
• RED LED illuminates.

Wiring diagram: 

• Telematics system Ref. to WIRING SYSTEM>TELEMATICS SYSTEM>WIRING DIAGRAM
• CAN communication system Ref. to WIRING SYSTEM>CAN COMMUNICATION SYSTEM>WIRING DIAGRAM

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK DTC  .
   1. Turn the ignition switch to ON.
   2. Read the DTC of [Telematics] using the Subaru Select Monitor. Ref. to TELEMATICS SYSTEM (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) 

   Is DTC U115B displayed? (Current code)

   Yes  : Go to  2.

   No  : Even if DTC is displayed, 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. 

2. CHECK HARNESS (OPEN CIRCUIT)  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the airbag control module connector.
   3. Disconnect the DCM connector.
   4. Using a tester, measure the resistance between the DCM connector and airbag control module connector.
      CAUTION:

      To measure the voltage and resistance of airbag system component, be sure to use the specified test harness. Ref. to  AIRBAG (DIAGNOSTICS)>GENERAL DESCRIPTION 

      Connector & terminal 

      (i105) No. 6 - (8BF) No. 1:

      (i105) No. 16 - (8BF) No. 2:

   Is the resistance 10 Ω or less?

   Yes  : Go to  3.

   No  : Repair or replace the open circuit of harness.

3. CHECK HARNESS (GROUND SHORT CIRCUIT)  .

   Using a tester, measure the resistance between DCM connector and chassis ground.

   Connector & terminal 

   (i105) No. 6 - Chassis ground:

   (i105) No. 16 - Chassis ground:

   Is the resistance 1 MΩ or more?

   Yes  : Go to  4.

   No  : Repair or replace the short circuit of the harness.

4. CHECK THE CONNECTOR (SHORT CIRCUIT TO POWER SUPPLY)  .
   1. Turn the ignition switch to ON.
   2. Using a tester, measure the voltage between DCM connector and chassis ground.

      Connector & terminal 

      (i105) No. 6 (+) - Chassis ground (-):

      (i105) No. 16 (+) - Chassis ground (-):

   Is the voltage less than 5 V?

   Yes  : Go to  5.

   No  : Repair or replace the short circuit of the harness.

5. CHECK DCM (INTERNAL RESISTANCE)  .
   1. Turn the ignition switch to OFF.
   2. Using a tester, measure the internal resistance of DCM.

      Terminals 

      (i105) No. 6 - (i105) No. 16: (internal resistance of DCM)

   Is the resistance 114 - 126 Ω?

   Yes  : Go to  6.

   No  : Replace the DCM. Ref. to ENTERTAINMENT & MONITORING>DATA COMMUNICATION MODULE

6. CHECK AIRBAG CONTROL MODULE (INTERNAL RESISTANCE)  .
   1. Connect the airbag control module connector.
   2. Using a tester, measure the resistance between DCM connectors. (Measure the internal resistance of airbag control module from DCM connectors)

      Terminals 

      (i105) No. 6 - (i105) No. 16: (internal resistance of airbag control module)

   Is the resistance 114 - 126 Ω?

   Yes  : Go to  7.

   No  : Replace the airbag control module. Ref. to AIRBAG SYSTEM>AIRBAG CONTROL MODULE

7. CHECK DCM  .
   1. Restore the vehicle to its original state.
   2. Turn the ignition switch to ON.
   3. Using the Subaru Select Monitor, perform the clear memory of [Telematics]. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY
   4. Turn the ignition switch to OFF.
   5. Turn the ignition switch to ON.
   6. Wait for 1 minute.
   7. Read the DTC of [Telematics] using the Subaru Select Monitor. Ref. to TELEMATICS SYSTEM (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) 

   Is DTC U115B displayed? (Current code)

   Yes  : Replace the DCM. Ref. to ENTERTAINMENT & MONITORING>DATA COMMUNICATION MODULE

   No  : Even if DTC is displayed, 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.