An Oxygen Sensor is a little device that fits on the exhaust system of your car and monitors how much free oxygen is there. Pretty straight forward, but why would you need it? I’ll tell you why.
Way back in the day, all gasoline engines were carbureted. That means that they had a mechanical carburetor that used the physics of air moving through a restriction to suck fuel in to the air stream and then in to the engine. Worked great for a hundred years and still works perfectly in some applications but it’s not super precise. If you want performance, fuel economy and low emissions then electronic fuel injection is the way to go. But if you’re gonna have electronic fuel injection you also need a computer to run it, and that computer is gonna need a couple sensors so it can accurately meter fuel to the engine. The primary sensors are a Mass Air Flow sensor and, our buddy, the Oxygen sensor.
The oxygen sensor tells the computer how much oxygen there is in the exhaust (duh). If there’s too little oxygen in the exhaust then there must be too much unburned fuel (hydrocarbons) and the engine is running rich, if there’s too much oxygen then there must be too little fuel (running lean) and your engine is producing nitrogen oxide. Both these conditions are bad for your engine, bad for fuel economy/performance and bad for the environment. By monitoring how much oxygen is in the exhaust the computer can adjust how much fuel is being injected in to the engine and keep it running most efficiently.
OK so far? Now your car probably has at least two oxygen sensors. The “upstream” sensor is the one that does what I just described. There is also a “downstream” sensor and its’ primary job is to monitor the catalytic converter. The catalytic converters’ job is to burn off any remaining hydrocarbons from the exhaust and the downstream oxygen sensor checks to make sure that job is getting done.
Both these sensors will wear out and fail. They have myriad ways of failing and can throw an amazing number of Check Engine Light codes when they do. I’ll get in to that stuff in other posts.
I hope you’ve found this useful! Your Local Mechanic, All Tune and Lube Total Car Care Tempe Arizona