Circuit Description

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.

DTC will set when the following conditions are present:

• Purge solenoid diagnostic vacuum switch DTC is not set.
• No IAC DTCs are set.
• No MAP sensor DTCs are set.
• No TP sensor DTCs are set.
• No EGR DTCs are set.
• BARO is greater than 75 kPa.
• Engine coolant temperature is less than 230°F (110°C).
• Power-up intake air temperature is greater than -.4°F (-18°C).
• Intake air temperature is less than or equal to 194°F (90°C).
• Change in engine coolant temperature/intake air temperature is less than or equal to 194°F (90°C).
• Purge DC is greater than or equal to 90 percent.
• MAP is greater than or equal to 20 kPa, but less than or equal to 80 kPa.
• Throttle position is greater than or equal to 5 percent, but less than or equal to 60 percent.
• Engine speed is greater than or equal to 800 RPM, but less than or equal to 3000 RPM.