Note. For circuit reference, see WIRING DIAGRAMS article.
Circuit Description
Evaporative (EVAP) emissions canister purge is controlled by a solenoid valve which allows ported vacuum to purge canister when energized (purge on) by PCM. A vacuum switch in purge line is used to detect when system is being purged. PCM supplies and reads EVAP purge vacuum switch signal. If switch is open (purge detected) when not commanded by PCM, DTC will set.
Conditions required to set DTC are, no IAT, MAP, PCM or TP sensor DTCs set, DTC P0442 diagnostic test has passed and a continuous open purge flow condition is detected during diagnostic test (fuel tank pressure decreases to less than -11 in. H2O).