The Powertrain Control Module (PCM) sets the P0446 code if the vacuum decay rate is greater than a predetermined value.
Engine Light ON (or Service Engine Soon Warning Light)
Possible a noticeable fuel odor caused by the release of fuel vapors
P0446 Chevrolet Description
The Powertrain Control Module (PCM) monitors the performance of the Evaporative Emission (EVAP) system by applying a predetermined level of vacuum to the EVAP system then monitors the vacuum decay rate.