Conditions for Running the DTC

WARNING: This page is about a different car, the 2006 GMC Yukon XL, 2006 Chevrolet Suburban, and 2006 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0451 runs only when the engine-off natural vacuum small leak test, DTC P0442, executes.
The number of times this test runs can range from 0-2 per engine-off period. The length of the test can be up to 40 minutes.