EVAP Emission Control System Operation

The EVAP canister purge is controlled by a solenoid valve that allows the manifold vacuum to purge the canister. The engine control module (ECM) supplies a ground to energize the solenoid valve (purge on). The EVAP purge solenoid control is pulse-width modulated (PWM) (turned on and off several times a second). The duty cycle (pulse width) is determined by engine operating conditions including load, throttle position, coolant temperature and ambient temperature. The duty cycle is calculated by the ECM. The output is commanded when the appropriate conditions have been met. These conditions are:

• The engine is fully warmed up.
• The engine has been running for a specified time.
• The ECT reading is above 55°C (131 °F).

A continuous purge condition with no purge commanded by the ECM will set a DTC P1441.

Poor idle, stalling and poor driveability can be caused by:

• A malfunctioning purge solenoid.
• A damaged canister.
• Hoses that are split, cracked, or not connected properly.