Gasoline-engined vehicles are fitted with an EVAP control system.
The EVAP control system prevents gasoline vapors from escaping into the atmosphere. When fuel evaporates from the fuel tank, the vapors pass through vent hoses or tubes to the carbon-filled EVAP canister. They are temporarily held in the canister until they can be drawn into the intake manifold when the engine is running.
Location and configuration of EVAP canister varies with model, year and engine. Most are mounted on a frame rail (left or right) forward of the fuel tank. The Ram 1500-3500 trucks utilize two EVAP canisters, located side-by-side on the outside of the left frame rail, in front of the fuel tank.
The canister is purged by the EVAP canister purge solenoid at predetermined times and certain engine operating conditions.
The EVAP canister purge solenoid controls the vacuum that draws the vapors from the canister. The Powertrain Control Module (PCM) controls the solenoid. The PCM operates the solenoid by either switching the ground circuit on or off. When energized the solenoid prevents vacuum from reaching the EVAP canister. When not energized, the solenoid allows vacuum to flow to the EVAP canister. The purge solenoid is mounted to a bracket located near the left-rear side of the intake manifold.
The solenoid opens when the engine reaches normal operating temperature and the vehicle is moving.
The EVAP canister is sealed and maintenance-free. However, a periodic inspection of the unit and vent hoses is advisable. Although the factory does not give recommendations here, you should inspect the unit at least every six months or 6000 miles (9600 km). During your inspection, make sure the unit is mounted firmly in its bracket, that it is not cracked and that the vent hoses are connected and not cracked. Correct any problems you may discover, or refer to the removal and installation procedure under "DRIVEABILITY AND EMISSION CONTROLS" if you suspect the unit itself is malfunctioning.