Also, #2 sensor (after cat) should be cycling slower than #1 sensor (in exhaust manifold).
Heres some info I posted yesterday from the FSM (it was for determining if a cat is bad, but the info on O2s is pertinent):
Check connections at the PCM and your wiring harness for backed out terminals, broken terminal locks, damaged terminals, and bad or worn wires. This especially includes the wiring on both 02 sensors.
If everything looks OK, then hook up your scan tool and watch the screen while moving connectors and wires that are related to the O2 sensors. A change in display will indicate a problem area.
Then monitor O2 sensor activity while in Park. If the activity level of both sensors is about equal, then there is a problem. Your 2nd O2 should show much less activity.
Then, if problem is still indicated, visually inspect the cat for dents, discoloration caused by severe temps, holes, or internal rattling. Also inspect exhaust downpipe and surrounding pieces for damage.
Mike: 1997 SE w/ 183K, aka White Horse
, Gutted Airbox w/K&N, drilled 180* t-stat, tint all around, clear corners w/SilverStars, "PONTIAC" light up tail, PEMs, NGK TR55s