I have this problem also with my 2001 Sonata GLS V6. Last Friday I went for an inspection (I live in NY), and after the mechanic connected my OBDII connector to his computer it gave two messages:
[b]Catalyst - not ready
[b]O2 sensor - not ready.
I was asked if I disconnected battery or did something else. No, I didn't do anything, last time on June the dealer replaced a timing belt, and since than I made over 2000 miles.
Then, somebody gave me an advice to check battery voltage while cranking. Yes, it dropped to 2V! Since the battery was original, 6 years old, I went to autoparts and replaced battery with new one.
Now, it's 2 days already and over 80 miles since I drive with new battery. I checked the car with "Scangauge II" scanner and it still showed "no codes found, not ready". Does anybody knows how long/how many trips/how many miles I have to drive to get it "ready"? Or I have some problem with the ECM?