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 FOR ANY OTHER DTC ON DISPLAY. 

   Is any other DTC displayed?

   • Yes: Check the appropriate DTC using the "List of Diagnostic Trouble Code (DTC)". Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>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 a general scan tool, read the values of [EVAP System Vapor Pressure] and [Mani. Absolute Pressure] to compare with actual atmospheric pressure.
   NOTE:

   • Subaru Select Monitor

     For detailed procedures, refer to "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>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 [EVAP System Vapor Pressure] is larger: Replace the leak check valve assembly. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>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) (H4DOTC)>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.
  NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.