Danger of a Faulty Purge Valve

by Edmund Gary

The purge valve is part of the EVAP (evaporative emission control) system of the automotive gasoline engine. The EVAP system prevents gases from entering the atmosphere while the engine is off. A faulty purge valve can compromise the EVAP system.

Extra Pollution

One danger of a faulty purge valve is the fuel vapors will escape from the fuel system and create a source of pollution. A properly working EVAP system traps the fuel vapors in the charcoal canister whenever the engine is off. When the car is started the trapped vapors are introduced into the combustion chamber (through the open purge valve) for burning.


A faulty purge valve can be caused by a leak in one of the hoses. A hole that is as small as a pin prick can be the source of the leak. Discovery of the leak can be made when technicians use special equipment called a smoke machine.

Faulty Canister

The charcoal canister can be affected by a bad purge valve. Faulty purge valves can cause the charcoal canister to become defective, providing that the valve is incorporated into the canister. Replacement of the canister may be the only option.

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