Diagnostic Aids
WARNING: This page is about a different car, the 1997 GMC Savana, 1997 Chevrolet Chevy Van, and 1997 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
Difficulty running OBD-II status DTC P0420 test may be encountered in areas where test conditions cannot be easily maintained, especially in urban areas.