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.

Failure detection pattern :

Detection by a single system (Primary Failure)

Warning light/indicator light :

Both ON -
GREEN LED ON -
GREEN LED blinks -
RED LED ON O
RED LED blinks -
Both OFF -

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.

CAUTION:

After the DCM is replaced, registrations of CommCheck and immobilizer system are required. Ref. to ENTERTAINMENT & MONITORING>TELEMATICS SYSTEM>OPERATION>REGISTRATION (COMM CHECK) .
Before performing diagnosis, refer to "CAUTION" in "General Description". Ref. to TELEMATICS SYSTEM (DIAGNOSTICS)>GENERAL DESCRIPTION>CAUTION .

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.
CHECK HARNESS (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 airbag control module connector.
3. Disconnect the DCM connector.
4. Connect the connector (1BF) in the test harness BF to the airbag control module connector.
5. Using a tester, measure the resistance between the DCM connector and the connector (8BF) in test harness BF.
  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.
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.
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.
CHECK DCM (INTERNAL RESISTANCE) .
1. Turn the ignition switch to OFF.
2. Connect the DCM connector (i105).
3. Using a tester, measure the resistance between connectors in test harness BF. (Measure the internal resistance of DCM from the test harness 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
  
  (8BF) No. 1 - (8BF) No. 2: (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 .
CHECK AIRBAG CONTROL MODULE (INTERNAL RESISTANCE) .
1. Disconnect the DCM connector.
2. Connect the airbag control module connector.
3. Using a tester, measure the resistance between DCM connectors. (Measure the internal resistance of airbag control module from DCM connectors)
  Connector & terminal
  
  (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 .
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.