Computers, software and fuel injectors can take most of the credit in lowering tailpipe emissions over the past three decades, but the oxygen sensor is the key that allows the other components to do their job properly.
The Robert Bosch Corp. pioneered the O2 sensor, starting with its first OEM installation on a 1976 Volvo 240/260 series. Also called the lambda sensor, an O2 sensor measures the oxygen content in the exhaust and signals the engine-management computer to adust the air-fuel ratio in the intake system for maximum efficiency. It can also monitor the catalytic converter function.
Many vehicles have multiple O2 sensors. The Ferrari Scaglietti 612 has 8: one for each of the four stainless-steel exhaust manifolds on the V12 engine and upper and lower sensors for the two catalytic converters.
Now's the time to offer a toast to the O2 sensor. Without it we'd still be running open-loop fuel-injection systems that couldn't be adjusted to real-time conditions and no one would pass their smog test.