Evaporative Emission Control System

Comp. Loc:

DESCRIPTION
An Evaporative Emission (EVAP) control system is used to prevent emission of fuel vapor.

OPERATION
The vapor generated in the fuel tank while driving, or with the engine at a stop, passes through a Tank Pressure Control valve and enters the EVAP canister where charcoal absorbs and stores the fuel vapor.

EVAP Canister
The Enhanced EVAP canister is purged (cleaned) in the same way as non-Enhanced EVAP Control Systems.

Tank Pressure Control Valve
The Tank Pressure Control valve operates as follows:

^ As the EVAP Tank Pressure Control Solenoid vacuum valve closes under the following conditions, the vapor passage of the Tank Pressure Control valve also closes.

- Engine "OFF".
- Engine is running, vehicle stopped and fuel level is higher than specified value.

Therefore, when the pressure of the vapor generated in the fuel tank increases higher than specified pressure, it pushes open the Tank Pressure Control valve and enters the EVAP canister.

However, under the conditions that the engine is running and the fuel level is lower than the specified value (or the vehicle is running and the fuel level is higher than the specified value), the EVAP Tank Pressure Control Solenoid vacuum valve is turned "ON" by the ECM and vacuum is applied to the diaphragm of the Tank Pressure Control valve. Thus, the vapor passage of the Tank Pressure Control valve opens to allow continuity between the fuel tank and the EVAP canister.

EVAP Canister Vent Solenoid
The EVAP Canister Vent solenoid and the Fuel Tank Pressure sensor are installed so that the ECM diagnosis leakage of fuel vapor from the EVAP Control System. The EVAP Canister Vent solenoid is usually open but it is closed by the ECM when checking for any leakage.

RESULTS OF INCORRECT OPERATION
Poor idle, stalling and poor driveability can be caused by:

^ Damaged Evaporative Emission (EVAP) canister.
^ Hoses split, cracked and/or not connected to the proper tubes.
^ Malfunctioning purge solenoid.