The 1998-2000 GMC Suburban 2500 has a known issue with the air pump check valve which causes illumination of the check engine light. There are no notable symptoms, but the vehicle will not pass state inspection or smog testing.

When the valve fails, it sticks closed, and the computer sets the code P1416. Replacement of the check valve is the only fix, as the valve is not serviceable.

This page can provide more information about the air pump check valve.