Canister Purge Solenoid: Description and Operation

EVAP Vacuum Switch:

Canister purge is controlled by an EVAP purge solenoid valve that allows manifold vacuum to purge the canister The Powertrain Control Module (PCM) supplies a ground to energize the EVAP purge solenoid valve (purge ON ). The EVAP purge solenoid control is Pulse Width Modulated (PWM) or turned ON and OFF several times a second. The PCM controlled PWM output is commanded when the following conditions have been met:
^ Engine coolant temperature above 25°C (77°F).
^ After the engine has been running about 2 1/2 minutes on a cold start or 30 seconds on a warm start.
^ The vehicle is operating in closed loop fuel control.

Canister purge PWM duty cycle varys according to operating conditions determined by mass air flow, fuel trim, and. intake air temperature. Canister purge will be disabled if Throttle Position (TP) angle increases to above 70%. Canister purge will be re-enabled when TP angle decreases below 66%. The EVAP vacuum switch is a normally closed switch positioned in the purge line between the canister and the EVAP purge valve. The EVAP vacuum switch will open when vacuum increases to greater than 5 inches of water in the purge line. The EVAP vacuum switch is used by the PCM to monitor EVAP purge valve operation and purge system integrity. The EVAP vacuum switch should be closed with no vacuum present (0% EVAP Purge PWM). With EVAP Purge PWM at 25% or greater, the EVAP vacuum switch should open.

Poor idle, stalling and poor driveability can be caused by the following conditions:
^ Malfunctioning EVAP purge valve.
^ Damaged canister.
^ Hoses split, cracked and/or not connected properly.

An incorrect EVAP purge system flow should set a DTC P0441. A continuous purge condition with no purge commanded by the PCM should set a DTC P1441.