DTC P0451: EVAP System (CPC) Pressure Sensor/Switch Circuit Range/Performance: Notes

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

1. CHECK DTC  .

   Read the engine DTC using the Subaru Select Monitor or general scan tool. Ref. to ENGINE (DIAGNOSTICS) (EXCEPT FOR STI)>Read Diagnostic Trouble Code (DTC) .

   Is DTC other than P0451 displayed? (Current malfunction)

   Yes: Check the appropriate DTC using the "List of Diagnostic Trouble Code (DTC)". Ref. to ENGINE (DIAGNOSTICS) (EXCEPT FOR STI)>List of Diagnostic Trouble Code (DTC) .

   No: Go to  2.

2. CHECK CURRENT DATA  .
   1. Turn the ignition switch to ON (engine OFF).
   2. Using the Subaru Select Monitor or general scan tool, read the value in «Absolute Evap Sys. Pressure» and «Mani. Absolute Pressure», and compare them with the actual atmospheric pressure.
      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.

      • To read the actual atmospheric pressure, connect the Subaru Select Monitor or general scan tool to the other known good vehicle.

   Is the difference with the actual atmospheric pressure 6.2 kPa (46.5 mmHg, 1.8 inHg) or more?

   Yes: Replace the part that showed larger deviation from the actual atmospheric pressure than the other.

   • If deviations in value for «Absolute Evap Sys. Pressure» is larger: Replace the leak check valve assembly. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (EXCEPT FOR STI)>Leak Check Valve Assembly .
   • If deviations in value for «Mani. Absolute Pressure» is larger: Replace the manifold absolute pressure and intake air temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (EXCEPT FOR STI)>Manifold Absolute Pressure and Intake Air Temperature Sensor .

   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.