DTC P0A12: Dc/Dc Converter Enable Circuit Low: Notes

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

Trouble symptom: 

• Auto Start Stop does not operate.
• When the Auto Start Stop restarts, the audio or navigation system is reset.

Wiring diagram: 

Auto Start Stop Ref. to WIRING SYSTEM>AUTO START STOP .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK SYSTEM OPERATION STATUS IN TCM  .
   1. Using the Subaru Select Monitor, perform the active test [Sub power supply control (ON/OFF Dr.)]. Ref. to AUTO START STOP (DIAGNOSTICS)>ACTIVE TEST .
   2. Read the data of [DC/DC Converter 1 Boost Signal Reception] using Subaru Select Monitor. Ref. to AUTO START STOP (DIAGNOSTICS)>DATA MONITOR .

   Does the display of [DC/DC Converter 1 Boost Signal Reception] change from [OFF] to [ON] according to the ON/OFF operation?

   Yes:  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  .

   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 in harness between ECM connector and DC/DC converter 1 connector.

      Connector & terminal 

      (B134) No. 7 - (B562) No. 11:

   Is the resistance less than 1 Ω?

   Yes:  Go to  3.

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

3. CHECK HARNESS BETWEEN ECM AND DC/DC CONVERTER 1  .

   Measure the resistance between ECM connector and chassis ground.

   Connector & terminal 

   (B134) No. 7 - Chassis ground:

   Is the resistance 1 MΩ or more?

   Yes:  Go to  4.

   No:  Repair the short circuit to ground in harness between ECM and DC/DC converter 1.

4. CHECK DC/DC BOOST OUTPUT SIGNAL  .
   1. Connect the ECM connector.
   2. Turn the ignition switch to ON.
   3. Using the Subaru Select Monitor, perform the active test [Sub power supply control (ON/OFF Dr.)]. Ref. to AUTO START STOP (DIAGNOSTICS)>ACTIVE TEST .
   4. Measure the voltage between ECM connector and chassis ground.

      Connector & terminal 

      (B134) No. 7 (+) - Chassis ground (-):

   Is the voltage still less than 5 V after ON/OFF operation?

   Yes:  Check for poor contact of ECM connector. Replace the ECM if no fault is found, Ref, to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Engine Control Module (ECM)  .

   No:  Check for the poor contact of DC/DC converter 1 connector. Replace the DC/DC converter 1 if no fault is found. Ref. to STARTING/CHARGING SYSTEMS (H4DO)>AUTO START STOP DC/DC CONVERTER .