DTC U0401 Invalid Data Received From ECM/Pcm "A": Wiring Diagram

CAN communication system. See appropriate SYSTEM WIRING DIAGRAM article.

Fig 1: CAN Communication System - Wiring Diagram

G08585509

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE

Step	Check	Yes	No
1 CHECK DTC. Check the displayed DTC.	Are DTCs other than U*** displayed?	Perform the diagnosis according to DTC.	Go to step 2 .
2 CHECK DTC. Check the displayed DTC.	Is DTC for the buss off or the data no-receive displayed?	Perform the diagnosis according to DTC.	Go to step 3 .
3 CHECK DTC. Check the displayed DTC.	Is U0401 a current malfunction?	Go to step 4 .	Go to step 8 .
4 CHECK DTC. Turn the ignition switch to OFF. Disconnect the ECM connector. Connect the disconnected connectors. Read the DTC using Subaru Select Monitor.	Is U0401 a current malfunction?	Go to step 5 .	Go to step 8 .
5 CHECK DTC. Using the Subaru Select Monitor, read DTC of all the systems.	Is the engine data abnormal detected in several modules?	Replace the ECM. Refer to ENGINE CONTROL MODULE (ECM) .	Go to step 6 .
6 REPLACE MODULE. Replace the ECM. Read the DTC using Subaru Select Monitor.	Is U0401 a current malfunction?	Go to step 7 .	System is normal.
7 CHECK MODULE. Reinstall the ECM. Replace the module that the DTC has been detected. Read the DTC using Subaru Select Monitor.	Is U0401 a current malfunction?	Replace the ECM. Refer to ENGINE CONTROL MODULE (ECM) .	System is normal.
8 CHECK HARNESS. Shake the harness, and check for poor contact. Using the Subaru Select Monitor, read DTC of CAN system.	Is U0401 a current malfunction?	Repair the poor contact of harness, or replace the harness.	Go to step 9 .
9 CHECK CONNECTOR. Check the connector used for high speed CAN for poor contact.	Is there poor contact of connector?	Repair the connector that has poor contact, or replace harness.	It is possible that temporary poor communication occurs. Delete the DTC.