DTC U0420: Invalid Data Received From Power Steering Control Module

DTC detecting condition: 

Defective data was transmitted from EPS control module.

Trouble symptom: 

Cooperation control with EPS control module does not operate properly.

1. CHECK CAN COMMUNICATION HARNESS. 

   Perform the basic diagnostic procedure to check for fault in CAN communication harness. Refer to LAN SYSTEM (DIAGNOSTICS) (EXCEPT FOR HEV)>BASIC DIAGNOSTIC PROCEDURE .

   Was the basic diagnostic procedure performed up to step 7?

   Yes:  Go to  2.

   No:  Perform the basic diagnostic procedure. Refer to LAN SYSTEM (DIAGNOSTICS) (EXCEPT FOR HEV)>BASIC DIAGNOSTIC PROCEDURE .

2. 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.

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.

4. CHECK DTC. 

   Check the displayed DTC.

   Is DTC U0420 displayed? (Current malfunction)

   Yes:  Go to  5.

   No:  Go to  7.

5. CHECK DTC. 
   1. Turn the ignition switch to OFF.
   2. Disconnect the power steering control module connector.
   3. Connect the disconnected connectors.
   4. Using the Subaru Select Monitor, read all DTCs. Refer to LAN SYSTEM (DIAGNOSTICS) (EXCEPT FOR HEV)>DIAGNOSTIC TROUBLE CODE (DTC)>OPERATION .

      Is DTC U0420 displayed? (Current malfunction)

   Yes:  Go to  6.

   No:  Go to  7.

6. CHECK DTC. 

   Using the Subaru Select Monitor, read all DTCs. Refer to LAN SYSTEM (DIAGNOSTICS) (EXCEPT FOR HEV)>DIAGNOSTIC TROUBLE CODE (DTC)>OPERATION .

   Is DTC U0420 detected in several modules? (Current malfunction)

   Yes:  Replace the power steering control module. Refer to POWER ASSISTED SYSTEM (POWER STEERING)>POWER STEERING CONTROL MODULE .

   No:  Replace the module that the DTC has been detected.

7. CHECK HARNESS. 
   1. Shake the harness and check for poor contact.
   2. Using the Subaru Select Monitor, read all DTCs. Refer to LAN SYSTEM (DIAGNOSTICS) (EXCEPT FOR HEV)>DIAGNOSTIC TROUBLE CODE (DTC)>OPERATION .

      Is DTC U0420 displayed? (Current malfunction)

   Yes:  Repair the poor contact of harness or replace the harness.

   No:  Go to  8.

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.