Possible Causes & Corrections:

WARNING: This page does not describe the selected car, but rather 35 other vehicles, including the 1992 Pontiac Trans Sport, 1992 Oldsmobile Silhouette, 1992 Oldsmobile Bravada, 1992 GMC Yukon, and 1992 GMC Vandura Special. However, it is still accessible from the selected car via links, so may be relevant.

Check for lead contamination of catalytic converter. Check for removal/tampering at restrictor in fuel filler neck.
Ensure air is not being diverted to exhaust manifold and is being diverted to catalytic converter during normal engine operation.
If emission test shows excessive carbon monoxide (CO) and hydrocarbons (HC) emissions and vehicle emits odor, check all systems and components which could cause engine to run rich. See DIAGNOSTIC AIDS in CODE 45 chart in appropriate G - TESTS W/ CODES article.
If emission test shows excessive oxides of nitrogen (NOx) emissions, check all systems and components which could cause engine to run lean or too hot. See DIAGNOSTIC AIDS in CODE 44 chart in appropriate G - TESTS W/ CODES article.