Q: What is the role of the fuel evaporative emissions control (EVAP) system,Purge Valve,Fuel Pressure Sensor and Canister for Chevrolet Colorado and GMC Canyon?
A: Fuel evaporative emissions control (EVAP) system is the system responsible for managing the fuel vapors from the fuel tank, and releases them into engine intake during engine operation. Key elements of this system include a canister which has activated charcoal that absorbs fuel vapors, purge valve, vent valve, fuel tank pressure sensor, fuel tank, and various vapor lines and purge lines. After going through a check valve, the fuel tank vapor goes to a charcoal canister where it is absorbed and stored by the charcoal.There are certain conditions under which PCM (Powertrain Control Module) will open both the purge and vent valves resulting in drawing of fuel vapors from canister into manifold for combustion within the intake manifold.The PCM regulates vapor flow rate through EVAP purge valve control solenoid by cycling it on and off so as to optimize purge based on engine conditions. During cold start-up mode of operation, this system self-diagnoses by creating vacuum in EVAP system to detect leaks while PCM monitors the voltage of Fuel Tank Pressure Sensor.The Fuel Tank Pressure Sensor supplies MAP Sensor like signal voltage to PCM representing air pressure within the fuel tank. Replacement procedures usually entail disconnecting quick connect fittings then cleaning area before removing mounting bolts; hoses; electrical connectors etc. Specific removal and installation procedure for replacing EVAP canister, purge valve, vent valve and fuel tank pressure sensor.This is because there is an EPA-mandated warranty that covers this evaporative emission control system.