Federal Emissions

EVAPORATIVE EMISSION SYSTEM
The Evaporative Emission (EVAP) system is used to absorb fuel vapors from the fuel tank. In a hot soak condition, fuel vapor pressure increases in the fuel tank. In order to reduce hydrocarbon emission into the atmosphere, fuel vapors are passed through a rollover/vent valve and into an EVAP canister. These fuel vapors are stored in the EVAP canister until they can be consumed in the engine. Under average driving conditions, the Powertrain Control Module (PCM) will purge the EVAP canister. This purging is controlled by the Exhaust Gas Recirculation/Evaporative Emission (EGR/EVAP) control solenoid. The EGR/EVAP control solenoid normally allows vapors to flow into the engine intake manifold to be burned unless the EGR/EVAP control solenoid is ON (ground supplied by the PCM). The PCM allows purging of the EVAP system except under:
- Engine starting condition
- Low engine coolant temperature condition
- Excessively high engine coolant temperature condition
- Engine idling condition
- High engine speed condition
- Mass air flow sensor failure





EGR/EVAP CONTROL SOLENOID
The Exhaust Gas Recirculation/Evaporative Emission (EGR/EVAP) control solenoid is controlled by the Powertrain Control Module (PCM). The EGR/EVAP control solenoid controls vacuum to both the Exhaust Gas Recirculation (EGR) valve and to the Evaporative (EVAP) emission canister. When the EGR/EVAP control solenoid is OFF (open signal from the PCM), vacuum is supplied to the EVAP canister and purging of the vapors in the EVAP canister is allowed. When the EGR/EVAP control solenoid is ON (ground supplied by PCM), vacuum is vented to the atmosphere prohibiting purging of the EVAP system. The PCM will command the EGR/EVAP control solenoid on at:
- Engine starting condition
- Low engine coolant temperature condition
- Excessively high engine coolant temperature condition
- Engine idling condition
- High engine speed condition
- Mass air flow sensor failure





EVAPORATIVE EMISSION CANISTER
The Evaporative Emission (EVAP) canister is a storage device for fuel vapors that are emitted by the fuel tank in hot soak conditions. When the vehicle is at normal operating conditions, the vapors are purged from the EVAP canister. The EVAP canister is controlled by the Exhaust Gas Recirculation/Evaporative Emission (EGR/EVAP) control solenoid. This solenoid sends vacuum to the EVAP canister purge valve (part of the EVAP canister) which allows the passage of the fuel vapors into the intake manifold where they are mixed with air and burned in the engine. By storing the fuel vapors and purging them into the engine at a later time, hydrocarbon emissions are reduced, and fuel efficiency is increased.





ROLLOVER/VENT VALVE
The rollover/vent valve controls pressure between the fuel tank and the Evaporative Emission (EVAP) canister. The rollover/vent valve will allow pressure to go either way, depending on the pressure applied to the valve. When the fuel in the tank is hot, pressure increases. The rollover/vent valve releases the fuel vapors into the EVAP canister to reduce the pressure in the fuel tank. If a rollover situation occurs the rollover/vent valve closes and will not permit fuel to escape from the fuel tank.