K 3500 Truck 4WD V8-454 7.4L VIN J SFI (1996)
Thermal Vacuum Valve - EVAP: Description and Operation
EVAP Vacuum Switch
The EVAP Purge Vacuum Switch is used by the VCM to monitor EVAP canister purge solenoid operation and purge system integrity. The EVAP Purge
Vacuum Switch should be closed to ground with no vacuum present (0% EVAP Purge Pulse Width Modulation (PWM). With EVAP Purge PWM at
25% or greater, the EVAP Purge Vacuum Switch should open.
