Purge Flow Sensor: Description and Operation

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 Canister Purge PWM). With EVAP Canister Purge PWM at 25% or greater, the EVAP Vacuum Switch should open.

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.