DTC U1604: Lost Communication With Dc/Dc Converter Module 1: Notes

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

Wiring diagram: 

Auto Start Stop Ref. to WIRING SYSTEM (CROSSTREK MODEL (EXCEPT FOR HEV))>AUTO START STOP .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK DTC  .

   Read the DTC of [Engine] using the Subaru Select Monitor. Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.5)>DATA MONITOR . Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.0 (EXCEPT FOR HEV))>DIAGNOSTIC TROUBLE CODE (DTC) .

   Is DTC U0077 displayed?

   Yes:  Perform the diagnosis according to the DTC. Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.5)>DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)>DTC U0077 LIN COMMUNICATION BUS "ECM/PCM" OFF . Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.0 (EXCEPT FOR HEV))>DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)>DTC U0077 LIN COMMUNICATION BUS "ECM/PCM" OFF .

   No:  Go to  2.

2. CHECK HARNESS BETWEEN ECM AND DC/DC CONVERTER 1  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the ECM connector.
   3. Disconnect the DC/DC converter 1 connector.
   4. Measure the resistance between ECM connector and DC/DC converter 1 connector.

      Connector & terminal 

      (B134) No. 17 - (B562) No. 9:

   Is the resistance less than 1 Ω?

   Yes:  Go to  3.

   No:  Repair the open circuit in harness between ECM connector and DC/DC converter 1 connector.

3. CHECK INPUT VOLTAGE OF DC/DC CONVERTER 1  .
   1. Turn the ignition switch to ON. (With the connector disconnected)
   2. Measure the voltage between DC/DC converter 1 connector and chassis ground.

      Connector & terminal 

      (B562) No. 12 (+) - Chassis ground (-):

   Is the voltage 12 V or more?

   Yes:  Go to  4.

   No:  Repair the open harness or broken fuse of power supply circuit.

4. CHECK HARNESS BETWEEN DC/DC CONVERTER 1 AND CHASSIS GROUND  .
   1. Turn the ignition switch to OFF.
   2. Measure the resistance between DC/DC converter 1 connector and chassis ground.

      Connector & terminal 

      (B563) No. 4 - Chassis ground:

   Is the resistance less than 5 Ω?

   Yes:  Go to  5.

   No:  Repair the open circuit of harness between DC/DC converter 1 connector and chassis ground.

5. CHECK REPEATABILITY  .
   1. Using the Subaru Select Monitor, perform the clear memory of [Auto Start Stop]. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY .
   2. Execute the inspection mode. Ref. to AUTO START STOP (DIAGNOSTICS)>INSPECTION MODE .

   Is DTC U1604 displayed?

   Yes:  Check for the poor contact in DC/DC converter 1 connector and ECM connector. Replace the DC/DC converter 1 if no fault is found. Ref. to STARTING/CHARGING SYSTEMS (H4DO (EXCEPT FOR HEV))>AUTO START STOP DC/DC CONVERTER .

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

   NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.