Circuit Description
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 1997 GMC Yukon, 1997 GMC Suburban, 1997 GMC Pickup, 1997 GMC Cab & Chassis, and 1997 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
Canister purge is controlled by a solenoid valve that allows ported vacuum to purge canister when energized. VCM supplies ground to energize solenoid valve which is pulse width modulated. Duty cycle is determined by closed loop feedback from HO2S. Duty cycle is calculated by VCM and output is commanded when certain conditions have been met.
A vacuum switch in purge line is used to detect when system is being purged. Normally closed switch will open when less than one in. Hg is present in purge line. VCM supplies a 12-volt reference to switch to monitor if evaporative emission control system is operating properly. DTC will set if switch is closed when VCM is commanding purge.