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 open when VCM is not commanding purge.

DTC will set when the following conditions are present:

• EVAP vacuum switch state equals high vacuum for a period greater than 4 seconds.
• 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).
• Intake air temperature is less than 194°F (90°C).
• Difference between engine coolant temperature and intake air temperature is less than 194°F (90°C).
• Purge DC is less than or equal to 5 percent.
• Manifold absolute pressure is greater than 20 kPa but less than 80 kPa.
• Throttle positions is greater than 5 percent but less than 60 percent.
• Engine speed is greater than 800 RPM but less than 3000 RPM.