Canister Vent Restriction Test

After the small leak test has passed, a vacuum is retained in the EVAP system. The control module tests for a restricted vent path by commanding the purge valve OFF (closed) and the vent valve OFF (open). The FTP sensor is monitored for a decrease in EVAP system vacuum. If the vacuum does not decrease to near 0 inch H2O in a calibrated time, DTC P0446 will set.