My Vios cars catalytic converter is bugging me for several months now. Scanners says catalytic converter below efficiency. I talk with couple of mechanics and some say iI need to change the O2 sensor, and some says i need to replace the catalytic converter which happens to be the three quarter of the exhaust pipe. cost of the genuine part is nearly 1 Lahk. Does any one know what needs to be done, Can i clean it without replacing ? I can go for a second hand part which will cost me about 20K but no guarantee.