GM 12559015 Valve,Evap Emission Canister Control

To prevent fuel system vapours from escaping to the atmosphere, the Evaporative Emissions Control (EVAP) system is designed. On hot days, the fuel tank's trapped vapors expand and when pressure reaches a certain level, they flow through valves into EVAP canister for temporary storage. When conditions are right, the Powertrain Control Module (PCM) opens the canister purge solenoid, allowing vapors to be drawn into the intake manifold and consumed by the engine. The EVAP canister is usually located on top of gas tank between 1996 and 2002 or beneath car from 2003 onwards. A normally open EVAP canister vent valve closes off system during testing and pressure checks; it is placed close to canister. The vapor pressure in the fuel tank is monitored by a fuel tank pressure sensor which is located above it. Vapor flow into the intake manifold is regulated by PCM-controlled EVAP canister purge solenoid. Symptoms include odor of gas, rough idle, stalling and other drive ability problems. The presence of excessive fuel vapor pressure can be checked by removing the gas cap. To replace components: Disconnect battery remove and reinstall either purge solenoid or vent valve depending upon model years.

Fuel tank vapor is directed through a check valve into the charcoal canister, where activated charcoal absorbs the vapors. When specific conditions are met (e.g., engine running, preset temperature reached), the ECM/PCM opens both the purge valve and vent valve. This action allows fuel vapors from the canister to be drawn into the intake manifold and combustion chamber, where they are consumed during engine operation. The ECM/PCM controls the vapor flow rate by modulating the EVAP purge valve control solenoid's duty cycle.

Fuel tank vapor is directed through a check valve into the charcoal canister, where activated charcoal absorbs the vapors. When specific conditions are met (e.g., engine running, preset temperature reached), the ECM/PCM opens both the purge valve and vent valve. This action allows fuel vapors from the canister to be drawn into the intake manifold and combustion chamber, where they are consumed during engine operation. The ECM/PCM controls the vapor flow rate by modulating the EVAP purge valve control solenoid's duty cycle.