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The purge valve is the part of the vehicle Evaporative Emission Control (EVAP) system. The EVAP system prevents fuel vapors in the fuel tank from escaping into the atmosphere. The EVAP system traps fuel vapors from the fuel tank and temporarily stores them in the charcoal canister. When the engine is running under certain conditions, the fuel vapors are purged from the canister and burned inside the engine.

The most common problem with the purge valve is when it sticks or does not close fully. This may cause the "Check Engine" warning light to come on with the code P0441. In some cars, a stuck-open purge valve can cause difficulty starting right after refueling at a gas station: for the first few seconds the engine may run rough and stumble.

For your engine to run smoothly and efficiently. An air to fuel ratio of 14.7:1 is to be maintained. Modern cars use oxygen sensors in exhaust to make sure that this ratio is maintained. If there is too much oxygen in exhaust, the short term fuel trim goes negative, hence allowing more fuel into the engine. And vice versa.

A faulty oxygen sensor or a leaks in exhaust or problems with fuel or fuel injectors can cause fuel trim to go positive. Thus under powering the vehicle. Such problems don’t normally turn the check engine light on.