MIL On in 1997 Protege DX... No Code :(
 

Hey guys, I have a 1997 Protege that is failing SMOG in CA because of the MIL being lit.

I've been driving the car with the light on for the last two years, but now its time to retest. Two years ago had it checked out, the code looked to be P0420. Today I used a friends' Snapon OBD computer tool, and I tried to pull the DTCs/pending DTCs, and there were none. I had reset the computer (pulled battery lead) about 100mi ago, and the light did come back on about 10mi into driving.

Now P0420 says that that bank 1 cat converter is operating below efficiency. Is this likely just an O2 sensor? Has anyone had experience with not being able to pull a code from the computer?