1995 Honda Del Sol not passing TN emissions testing - no check engine light on

He failed the hc and co. He failed the hc the first time before replacing the cat. Now he failed both. He is replacing the 02 sensor today. If that doesn't work, he doesn't know what to do next.

but,is he unhooking the battery each time he does work on the car?if so ,you have to dive the car thru a drive cycle,50-250 miles.highway,around town,stop and go driving, because the computer resets everything if the battery is unhooked.