When the engine runs, the Evaporative Emissions Control (EVAP) system collects fuel vapors, holds them in a canister filled with activated charcoal, and sends them through vacuum to the engine's intake system. When the engine is idle, the canister holds the vapors. The PCM makes the electronic purge control valve switch vapors into the engine while running. Diagnostics added to more recent models starting in 1997 help check the EVAP system's performance and find any leaks. The EVAP system may act up when the purge valve breaks down, the canister becomes damaged, or any of the connecting hoses wear out. Fuel smells and loss from leaks or worn hoses happen often. You need to check all parts carefully and fix anything that's broken. The canister must be replaced whenever it starts to crack or leak, but we can test the purge and vent valves using the same methods as we do for other solenoids. The EVAP system pressure sensor works like a
MAP Sensor, but it offers better accuracy as specific voltage levels tell us if all parts are working properly. Keep the system under 6.0 in-Hg pressure to maintain good health. To replace the canister on these vehicles, made after 1997, take out the canister from the left frame rail behind the fuel tank. On Frontier and Xterra models, find and remove the canister from behind the rear axle, on a crossmember. We must lift the vehicle, disconnect the vacuum wires, unscrew the holding screws, then do the opposite steps when putting the part back together.