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Oxygen Sensors

Q: When I was inspecting the exhaust system I noticed a small component with a wire going to it. What is this part?

A: What you are referring to is an oxygen (O2) sensor. In many vehicles there is an O2 sensor before and after the catalytic converter. Cars with two catalytic converters can have four O2 sensors. The O2 sensor monitors the exhaust gases and measures the oxygen content in the gases. It continuously reports the results to the car’s electronic control unit to maintain the most efficient air-fuel ratio. A faulty O2 sensor can cause the car to receive poor fuel economy, increased emissions, poor acceleration, rough idle, premature failure of the catalytic converter, and more.