Q:

How does a purge valve work in an EVAP system?

A:

Quick Answer

In an evaporative emission control system, the purge valve works by controlling the amount of vapor from the charcoal canister. In modern cars, the engine computer controls the purge valve.

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Full Answer

Since the engine computer controls the purge valve, when the engine is not running, the valve closes. When the engine runs, the purge valve slowly opens as the engine warms. This allows some of the vapor from the fuel to move from the charcoal canister to the engine. There are a number of sensors that monitor this exchange, and if the flow is abnormal, the vehicle's check engine light illuminates.

If the check engine light illuminates due to the purge valve, the car may not start immediately after refueling. If it does, it may stumble or run roughly. This is a common issue in vehicles, and the vehicle owner knows this is the case if seeing the code P0441. Some car brands that often have this issue include Hyundai, Volkswagen and Audi. Mazda vehicles also may have issues with the purge valve, but in this case, the code is P0446.

If the vehicle develops an issue with the purge valve, repairs range from $125 to $190, as of 2015. It is important to check the codes before making the repair, as these symptoms may also indicate other issues.

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