My car just failed the e-test and the first major problem was the catalytic converter but after that it improved greatly but still failed. I toke my car to school to check it out and get error codes 15,23, and 24. The error codes 15 and 23 are the l/h and r/h o2 sensors and error 24 is the closed loop circuit they are in but the scanner I used wouldn't actually give me a reading of what was going on. Does anyone know a good way to try and test the o2 sensors or would you say it is safe to spend my money and replace them? and I also did an exhaust test and found out my car is running rich. If anyone knows what's going on with my car feel free to help cause I want my car to pass that e-test and stop running so rich. Thanks a lot!