DTC U0431: Invalid Data Received From Body Control Module "A"

DTC detecting condition:

Defective data was transmitted from Front relay control module.

Trouble symptom:

Cooperation control with Front relay control module does not operate properly.

CAUTION: Before performing diagnosis, refer to "CAUTION" in "General Description". Ref. to LAN SYSTEM (DIAGNOSTICS)>GENERAL DESCRIPTION>CAUTION .

CHECK CAN COMMUNICATION HARNESS .
Perform the basic diagnostic procedure to check for fault in CAN communication harness. Ref. to LAN SYSTEM (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE .

Was the basic diagnostic procedure performed up to step 7?

Yes : Go to 2 .

No : Perform the basic diagnostic procedure. Ref. to LAN SYSTEM (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE .
CHECK DTC (OTHER THAN U-CODE) .
Check the displayed DTC.

Is DTC other than U*** displayed? (Current malfunction)

Yes : Perform the diagnosis for DTCs other than the displayed U-code.

No : Go to 3 .
CHECK DTC (U-CODE) .
Check the displayed DTC.

Is DTC for the bus off or the data no-receive displayed? (Current malfunction)

Yes : Perform the diagnosis for DTCs for the displayed bus off or the data no-receive.

No : Go to 4 .
CHECK DTC .
Check the displayed DTC.

Is DTC U0431 displayed? (Current malfunction)

Yes : Go to 5 .

No : Go to 7 .
CHECK DTC .
1. Turn the ignition switch to OFF.
2. Disconnect the Front relay control module connector.
3. Connect the disconnected connectors.
4. Using the Subaru Select Monitor, read all DTCs. Ref. to LAN System (Diagnostics)>Diagnostic Trouble Code (DTC) .
  Is DTC U0431 displayed? (Current malfunction)
  
  Yes : Go to 6 .
  
  No : Go to 7 .
CHECK DTC .
Using the Subaru Select Monitor, read all DTCs. Ref. to LAN System (Diagnostics)>Diagnostic Trouble Code (DTC) .

Is DTC U0431 detected in several modules? (Current malfunction)

Yes : Replace Front relay control module. Ref. to BODY CONTROL/COMMUNICATION SYSTEM>FRONT RELAY CONTROL MODULE .

No : Replace the module that the DTC has been detected.
CHECK HARNESS .
1. Shake the harness, and check for poor contact.
2. Using the Subaru Select Monitor, read all DTCs. Ref. to LAN System (Diagnostics)>Diagnostic Trouble Code (DTC) .
  Is DTC U0431 displayed? (Current malfunction)
  
  Yes : Repair the poor contact of harness, or replace the harness.
  
  No : Go to 8 .
CHECK CONNECTOR .
Check the connector used for high speed CAN for poor contact.

Is there poor contact of connector?

Yes : Repair the connector that has poor contact, or replace harness.

No : It is possible that temporary poor communication occurs. Delete the DTC.