GM 12559015 Valve,Evap Emission Canister Control

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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.

The role of the evaporative emissions control (EVAP) system is to manage fuel vapors by absorbing them from the fuel tank and then releasing into the engine's intake system where they will mix with incoming air/fuel mixture. The canister filled with activated charcoal for vapor absorption, purge valve, vent valve, fuel tank pressure sensor, fuel tank itself, and vapor and purge lines are some of the key components that make up this system though there might be slight variations in their components through different years and applications. The charcoal canister is a sealed carrier entered via a check valve by fuel tank vapor on its way through a second hose comprised of capillary slits which have been called vapor hose in order to let out or activate coal store the vapors. When certain conditions are met for instance; engine running or reaching preset temperature, the ECM/PCM opens both the purge valve as well as vent valve. Consequently, intake manifold vacuum drawn through a purge hose causes fumes from canister while normal engine operation consumes this fumes inside intake manifolds including combustion chambers. The EVAP purge solenoid is modulated by ECM/PCM to control the rate at which vapors flow from the canister to intake manifold. In cold conditions and during a hot start time delay, this solenoid remains de-energized according to ECM/PCEM. After warming up to operating temperature range specified for it, engine control module/ power control module (ECM/PCM) regulates purging of vapors into intake manifold based on engine running conditions. By varying energization time of solenoid OBD II models cycle purge valve control solenoid from 5 to 10 times per second for adjusting a flow rate. In such case PCM opens EVAP canister purge valve and closes vent valve during cold engine startup thereby creating vacuum throughout EVAP system after 1996 -2000 OBD-II models. PCM closes purge valve after reaching vacuum level, sealing the system and monitoring fuel tank pressure sensor voltage to set diagnostic code in case of leak detection. In these models, there is also a fuel tank pressure sensor that sends back a signal voltage to the PCM reflecting air pressure inside the fuel tank for detecting leaks. Of note, this system is protected by a five-year/ 50,000-mile warranty as mandated by federal law. In troubleshooting the system, start by checking hoses for damage, disconnection or misrouting. Repair any faulty hoses or replace them as required. For pre-EVAP controls model years check charcoal canister, purge control valve and vacuum hoses for possible problems. Late models contain electronic purge control so it is important to verify related fuses and wiring integrity pertaining to the purge and vent valves. These valves are typically closed with vapor flow starting following activation of PCM's solenoid. Although some limited testing may be performed, a scan tool must be used for thorough examination. If these initial checks do not identify the problem, consult a dealer service department or qualified repair shop. When replacing components, late model EVAP system hoses are equipped with quick-connect fittings requiring a twisting motion to loosen the seal before disconnection is made. The EVAP canister's location varies with the year and application while its removal involve disconnecting these hoses and removing bracket mounting bolt. During removal of early model vehicles, on top of electrical connector detachment one has to remove connecting lock tab on hose then take away mounting nuts/bolt from its intake manifold place or charcoal canister (Allen 83). On 1996-2000 models vent valve is mounted on bracket close to fuel tank which means raising of vehicle will have to occur since you should disconnect electrical connector from it then remove hose next release retainer in order displace vent valve from bracket (Allen 83). In 1996 through 2000 only, fuel tank pressure sensor is located on the fuel pump module hence removal of fuel tank follows disconnection of electrical connector and then releasing retaining clip to get rid of sensor from the pump (Allen 84). Put all replaced components back in place as we have done in reverse order.

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.