Enhanced Evaporative Emission (EVAP) Control System

PURPOSE
The Enhanced Evaporative Emission (EVAP) system is required to detect evaporative fuel system leaks as small as 0.040 in. between the fuel filler cap and the purge valve. The system can test the evaporative emission system integrity by applying a vacuum signal (ported or manifold) to the fuel tank. This will create a small vacuum that can be monitored for leaks.


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

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

The Tank Pressure Control valve operates as follows:
- When the EVAP Tank Pressure Control Solenoid vacuum valve closes under the following conditions, the vapor passage of the Tank Pressure Control valve also closes.
- The engine is OFF.
- The engine is running, the vehicle is stopped and the fuel level is higher than the specified value.

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


However, under the condition 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 PCM and the 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.
The EVAP Canister Vent solenoid and the Fuel Tank Pressure sensor are provided so that the PCM can diagnose fuel vapor leakage from the EVAP Control System. The EVAP Canister Vent solenoid is usually open but is closed by the PCM when checking for any leakage.


RESULTS OF INCORRECT OPERATION
Poor idle, stalling and poor driveability can be caused by:
^ A damaged Evaporative Emission (EVAP) canister.
^ Hoses that are split, cracked and/or incorrectly connected to the proper tubes.
^ A malfunctioning purge solenoid. Evidence of fuel loss or fuel vapor odor can be caused by:
^ Liquid fuel leaking from fuel pipes.
^ A cracked or damaged EVAP canister.
^ Disconnected, misrouted, kinked, deteriorated or damaged vapor hoses.
^ Broken or leaking solenoids and components.