Oxygen Sensors 101

So what exactly does an oxygen sensor do? The answer is in the name; An oxygen sensor measures the amount of unburned oxygen in the exhaust system left after combustion in the engine's cylinders. Based on the amount of Oxygen present, the sensor genrates a voltage which is read by the engine's fuel management system. Too much residual O2 in the exhaust, and the car's computer releases more fuel for the next combustion cycle; too little O2, and the opposite happens. This balancing act happens many times every second to maitain the optimal fuel to air ratio of 14.7 : 1. This ratio has been found to produce the most efficient combustion, and therefore, the most power.