DTC U171F: Lost Lin Communication With Generator: Notes

1. - 

DTC detecting condition: 

Immediately at fault recognition

Wiring diagram: 

Engine Electrical System Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK DTC  .
   1. Turn the ignition switch to ON.
   2. Using the Subaru Select Monitor or a general scan tool, read the DTC of [Engine]. Ref. to COMMON (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)

   Is DTC U171F displayed? (Current code)

   Yes  : Go to  2.

   No  : Even if DTC is detected, 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 TERMINAL B  .
   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 terminal B.

      Connector & terminal 

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

   Is the voltage battery voltage?

   Yes  : Go to  4.

   No  : Check the generator terminal B harness and fuse.

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

      Connector & terminal 

      (B61) No. 20 - (Bt52) 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 (H4DOTC)>GENERATOR

   No  : Repair the following item.

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