The fuel vapor canister, also known as a charcoal canister because it is filled with charcoal, is part of a vehicle's pollution control system and is used to capture fuel vapors emanating from both the fuel tank and the carburetor. The vapors are pulled into the fuel vapor canister by a vacuum as the engine is started, and then fed back into the fuel system to be burned when the engine is running. The fuel vapor canister is a component of a vehicle's evaporative emission control (EVAP) system and prevents the evaporating fumes from reaching the atmosphere while also maintaining proper fuel tank pressures.

In the mid 1970s, automobile manufacturers began installing pollution control systems on engines to aid in reducing emissions put into the atmosphere from automobiles. Studies found that a great deal of the hydrocarbons or HCs that were emitted from automobiles were due to evaporative gasses. By placing the fuel vapor canister in the fuel system, the gasses are drawn into the canister and then burned instead of entering the atmosphere. This makes for a cleaner burning engine and a better environment for everyone. This system is also used on fuel-injected vehicles with the only difference being the gasses are sent into the intake rather than the carburetor.

There is no required service for the fuel vapor canister beyond keeping the hoses and canister clean and free of debris. A cracked hose will cause the "check engine" light to illuminate in a vehicle's dashboard display area, alerting the driver to a potential problem with the vehicle. Other areas that may cause the warning light to be seen are a faulty fuel tank cap or a loose or incorrectly-tightened cap. There is also a valve on the fuel vapor canister and the intake that are both vacuum-activated and could cause the warning light to come on should a malfunction occur.

The most common reason for a failure in the fuel vapor canister is a crack in the canister or a hose. In order to test the fuel vapor canister, nitrogen is applied to create pressure, and then it is tested periodically for a drop in pressure. Any pressure drop will indicate a fault in either the canister or a hose. Once the problem component is identified, repair or removal of the affected piece is recommended. Nitrogen is always used to test for leaks due to the danger aspect of using shop air. Introducing air into the fuel vapor canister could result in a dangerous fire, explosion or other incident stemming from adding oxygen to the fuel vapors.