EVAP Canister Purge Valve
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
The EVAP canister purge valve controls the flow of fuel vapors from the EVAP system, to the intake manifold. The PCM will change the duty ratio cycle of the purge valve, controlling the purge flow volume. Purge flow volume is determined by manifold pressure, and the purge valves duty ratio cycle. Atmospheric pressure is allowed into the canister to ensure that purge flow is consistently maintained when ever purge vacuum is applied to the canister. The purge valve will also be opened during some portions of the EVAP system testing, allowing engine vacuum to enter the EVAP system.