Basic operation of an Oxygen (O2) Sensor: The O2 Sensor is basically a device that measures the oxygen content in the combustion results (exhaust gases) of an engine. The more oxygen in the exhaust gases, the leaner the mixture and the less oxygen, the richer the mixture. The working voltage is from 0v (0mv) to 1v (1000mv); the leaner the exhaust gases (more oxygen) the lower the voltage and the richer the exhaust gases (less oxygen) the higher the voltage leaving 500mv as the perfect mixture. If a volt meter is connected at the signal wire, the changing in voltage can be seen. The Electronic Control Module (ECM) tries to keep the voltage around 400mv to 600mv (lean to rich, rich to lean) and this is going on all the time while the engine is running. If the voltage signal from the O2 sensor is below 500mv (lean, too much oxygen), the ECM compensates by sending more fuel (gasoline) to the mixture and if is above 500mv (rich, not enough oxygen), it compensates by sending less fuel to the mixture.
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