Circuit Description

Evaporative Emission (EVAP) canister purge valve allows manifold vacuum to purge canister. Powertrain Control Module (PCM) supplies a ground to energize the solenoid (purge on). EVAP canister purge valve is turned on and off several times a second. The duty cycle (pulse width) is determined by engine operating conditions including load, throttle position, coolant temperature and ambient temperature. Duty cycle is calculated by PCM and the output is commanded when appropriate conditions have been met.

EVAP purge vacuum switch is a normally closed switch. EVAP purge switch will open when vacuum increases to greater than 5 in. H2O in purge line. PCM monitors EVAP purge vacuum switch signal to determine if EVAP system is functioning properly.

Conditions for setting DTC are:

• No active IAT, MAF, MAP, TP sensor DTC(s) set.
• IAT 32-158°F (0-70°C).
• EVAP purge vacuum switch is open during key on (before engine is cranked.)