Conditions for Setting the DTC

WARNING: This page is about a different car, the 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.

The control module detects weak vacuum during a purge condition.
The fuel tank vacuum is less than -1 inches H2O for 4 seconds continuously or 50 seconds cumulative, within 10 minutes of cold start.
The 11 second test can run up to 10 times within 10 minutes of cold start and must be completed before this DTC will set.