Code 64 - Right Oxygen (O2) Sensor Lean (3.4L "F" Body)
WARNING: This page is about a different car, the 1993 Pontiac Grand Prix, 1993 Pontiac Firebird, 1993 Oldsmobile Cutlass Supreme, 1993 Chevrolet Lumina, and 1993 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
See Code 44 chart and duplicate procedure for right O2 sensor as necessary.