Evaporative Emission Control System

Description and Operation

Description

The evaporative emission control system prevents fuel vapors stored in the fuel tank from being released into the atmosphere. When fuel evaporates in the fuel tank, the vapor passes through the vent hoses or tubes into the canister filled with activated charcoal, which temporarily holds the vapors. When the ECM determines that the conditions are right, it uses intake manifold vacuum to draw the collected vapors into the combustion chambers.

Circuit Diagrams

Schematic Diagram

1. Air cleaner 2. Delivery pipe and injector 3. Engine 4. Purge control solenoid valve (PCSV) 5. Low-pressure fuel pump

6. High-pressure fuel pump 7. Filler neck 8. Fuel filler cap 9. Fuel tank

Canister: The canister is filled with activated charcoal, which absorbs the fuel vapors evaporating in the fuel tank. The fuel vapors collected in the canister are drawn into the intake manifold by the ECM/PCM when the appropriate conditions are met. Purge Control Solenoid Valve (PCSV): The purge control solenoid valve (PCSV) is installed in the passage connecting the canister and the intake manifold. It is a normally closed solenoid valve, controlled by a signal from the ECM/PCM. To draw the absorbed vapors into the intake manifold, the ECM/PCM opens the PCSV; otherwise the passage remains closed. Fuel Filler Cap: A ratchet tightening mechanism on the threaded fuel filler cap reduces the likelihood of incorrect installation and ensures the filler neck is sealed. After the gaskets on the fuel filler cap and the filler neck flange contact each other, the ratchet produces a clicking sound, indicating the seal is installed.