DTC P0452: EVAP System (CPC) Pressure Sensor/Switch Circuit Low: Notes

DTC detecting condition: 

Immediately at fault recognition

• Use the check board when measuring the ECM terminal voltage and resistance.

Wiring diagram: 

Engine Electrical System Ref. to WIRING SYSTEM>Engine Electrical System>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK CURRENT DATA  .
   1. Turn the ignition switch to ON.
   2. Read the value of «Absolute Evap Sys. Pressure» using the Subaru Select Monitor or a general scan tool.
      NOTE:

      • Subaru Select Monitor

        For detailed operation procedures, refer to "Read Current Data For Engine". Ref. to ENGINE (DIAGNOSTICS) (EXCEPT FOR STI)>Subaru Select Monitor .

      • General scan tool

        For detailed operation procedures, refer to the general scan tool operation manual.

   Is the value in «Absolute Evap Sys. Pressure» 34 kPa (255 mmHg, 10 inHg) or less?

   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.

   NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.
2. CHECK POWER SUPPLY OF LEAK CHECK VALVE ASSEMBLY  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from the leak check valve assembly.
   3. Turn the ignition switch to ON.
   4. Measure the voltage between the leak check valve assembly connector and chassis ground.

      Connector & terminal 

      (R400) No. 6 (+) - Chassis ground (-):

   Is the voltage 4.5 V or more?

   Yes: Go to  3.

   No: Repair the harness and connector.

   NOTE: In this case, repair the following item:
   • Open circuit in harness between ECM connector and the leak check valve assembly connector
   • Poor contact of ECM connector
   • Poor contact of coupling connector
3. CHECK HARNESS BETWEEN ECM AND LEAK CHECK VALVE ASSEMBLY CONNECTOR  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from ECM.
   3. Measure the resistance between ECM connector and chassis ground.

      Connector & terminal 

      (B134) No. 15 - Chassis ground:

   Is the resistance 1 MΩ or more?

   Yes: Go to  4.

   No: Repair the short circuit to ground in harness between ECM connector and leak check valve assembly connector.

4. CHECK FOR POOR CONTACT  .

   Check for poor contact of leak check valve assembly connector.

   Is there poor contact in the leak check valve assembly connector?

   Yes: Repair the poor contact in the leak check valve assembly connector.

   No: Replace the leak check valve assembly. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (EXCEPT FOR STI)>Leak Check Valve Assembly .