Q: How do you know if catalytic converter is bad

To begin with, 170 thousand miles is just about the right time for the catalyst on a civic to start acting up. Your car is equipped with two oxygen sensors to monitor the catalytic converter function. The reaction that takes place in the catalytic converter consumes oxygen, so if the converter is working, the exhaust oxygen content will be lower coming out of the converter than it was going in. When the engine controller senses that the difference in the oxygen levels is not great enough, it will present a fault and light the check engine light. The engine controller performs a catalyst test once per drive cycle. If the catalyst passes the test a certain number of times the Controller will turn the light off. When the catalyst is in early stages of failure, it may pass the test sometimes and fail it at others, so you may have the check engine light going out for a while then coming back on. But the code is stored, so whether the light is on or not, the scanner will pick up the catalyst efficiency code. A bad catalyst may not affect the way the car runs at all. But you won’t be able to pass inspection with a bad catalyst, so sooner or later it will have to be changed. If you contact Your Mechanic,they can send a technician to your home or office to take care of the catalyst replacement for you.