Emmision test fails High CO out

More than likely it is a bad o2 sensor,but these can be ohmed to check continuty of it,your car is ob1 so it can not be hooked to a computer to tell you what is the actual problem,but if you know and old school mechanic he can run a test on it by counting the engine light flashes threw what is called a ob1 flash test.

Co, Carbon Monoxide, is removed by the catalytic convertor. click to size up

NOx is reduced by EGR and further eliminated by cat. But excessive CO is probably a cat problem