Purge Flow Sensor: Description and Operation

EVAP System:

EVAP Vacuum Switch:

The EVAP vacuum switch is a normally closed switch positioned in the purge line between the canister and the EVAP purge solenoid. 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 solenoid operation and purge system integrity. The EVAP vacuum switch should be closed to ground with no vacuum present (0% EVAP Purge PWM). With EVAP Purge PWM at 25% or greater, the EVAP vacuum switch should open.

IMAGE LEGEND
(1) EVAP Canister Purge Valve
(2) EVAP Vacuum Switch