Whether your vehicle is running or not, its tank should always contain some fuel. When it’s getting hotter this liquid fuel changes its state to gas, causing fuel vapors, which may destroy the tank if they are neglected. To keep this from happening, automakers equip their vehicles with an evaporative emission control system, which prevents vapors from escaping the tank, while protecting it from getting damage. The key role in this system is performed by a charcoal canister, which is filled with activated charcoal that absorbs fuel vapors.
In a vehicle, the charcoal canister is connected to the fuel tank through a hose or a linkage. It also features a purge valve and a vent valve. The first one serves to deliver fuel vapors to the combustion chamber when the engine is running, while the second one is used for testing the evaporative emission control system for leaks. It also lets fresh air in during purge. Both valves are operated by the engine control unit, which opens or closes the valves depending on the data received from different sensors throughout the vehicle.
Being a key component of the evaporative emission control system, a faulty charcoal canister or a clogged vent or purge valve will cause an array of engine-related problems. Here is the list of the most common failures:
Illuminated check engine light
If your charcoal canister gets clogged or cracked, your engine control unit will detect a lack of airflow or a system leak and turn on the check engine light.
Fuel vapors are very harmful to the environment. If the charcoal canister fails due to a crack or a clogged valve, the vapor will escape from the canister into the atmosphere.
Raw fuel smell
A leaking charcoal canister can allow raw fuel to escape into the outside air. As a result, you may notice a smell of fuel.
Problems at the pump
A clogged charcoal canister may prevent airflow, resulting in inability to refuel the vehicle.
Failed emissions test
A faulty or malfunctioning charcoal canister can lead to increased emissions, which is why you may not pass a regular emissions test.
Charcoal canister troubleshooting
A faulty charcoal canister is not repairable. It must be replaced with a brand-new unit as soon as possible to prevent damage to the tank and to keep the emissions below a certain level. Before replacing the canister, a proper diagnosis of the entire evaporative emission control system is recommended to avoid unnecessary repairs. This job should be left to a professional mechanic who will use a special scan tool or smoke machine to detect the problem and to test the system once the replacement is done.