EVAP Control System Diagnosis
WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
For EVAP control system diagnosis, see INSPECTION/MAINTENANCE EVAPORATIVE EMISSION SET PROCEDURE under DRIVE CYCLES in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article.