Operation A: Atmospheric Pressure Measurement
Purge VSV: OFF,
Operation B, E:
Reference Pressure Measurement
Vent Valve: OFF (vent) Canister Pump Module
Leak Detection Pump: OFF
Operation C: EVAP System Pressure Measurement
Reference Orifice (0.02 Inch)
Operation D: Purge VSV Monitor
(a)Purge VSV stuck open
In operation C, the leak detection pump creates negative pressure (vacuum) in the EVAP system. The EVAP system pressure is then measured by the ECM using the canister pressure sensor. If the stabilized system pressure is higher than [second reference pressure x 0.2], the ECM interprets this as the purge VSV (Vacuum Switching Valve) being stuck open. The ECM illuminates the MIL and sets the DTC (2 trip detection logic).
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