DTC U171F: Lost Lin Communication With Generator: Notes

DTC detecting condition: 

Immediately at fault recognition

Wiring diagram: 

Charging System Ref. to WIRING SYSTEM>CHARGING SYSTEM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK DTC  .

   Read the engine DTC using the Subaru Select Monitor or general scan tool. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

   Is DTC U171F displayed? (Current malfunction)

   Yes: Go to  2 .

   No: The circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again.

2. CHECK ECM CONNECTOR  .

   Check the connecting condition of ECM connector.

   Is the ECM connector correctly connected?

   Yes: Go to  3 .

   No: Connect the ECM connector correctly.

3. CHECK VOLTAGE OF GENERATOR B TERMINAL  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the ground terminal from battery sensor. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
   3. Measure the voltage of the generator B terminal.

      Connector & terminal 

      Generator terminal B (+) - Engine ground (-):

   Is it battery voltage?

   Yes: Go to  4 .

   No: Check the generator B terminal harness and fuse.

4. CHECK HARNESS BETWEEN ECM AND GENERATOR CONNECTOR  .
   1. Disconnect the connector from ECM.
   2. Disconnect the LIN communication connector from the generator.
   3. Measure the resistance of harness between ECM and LIN communication connector.

      Connector & terminal 

      (B134) No. 55 - (B471) No. 1:

   Is the resistance less than 1 Ω?

   Yes: Check the connector for poor contact and check the harness again. If no fault is found, replace the generator. Ref. to STARTING/CHARGING SYSTEMS (H4DO)>GENERATOR .

   No: Repair the harness and connector.

   NOTE: In this case, repair the following item:

   • Open circuit of harness between ECM connector and generator connector
   • Poor contact of coupling connector