Wide-band oxygen--or O2--sensors are beginning to come into their own as a performance item, but have actually been around for some time. These sensors can accurately monitor air/fuel ratios well outside the range of narrow-band sensors, and are crucial to tuning.
The wide-band O2 sensor was first patented by Robert Bosch GmbH in 1994 for emissions testing, but was rapidly miniaturized for use in automobiles.
O2 Sensor Purpose
The purpose of any oxygen sensor is to record a vehicle's exhaust gas heat, and to send the data to a computer to extrapolate the engine's air/fuel ratio in real time. A hotter exhaust stream means too little fuel to the engine, and a colder one means it's getting too much.
While narrow-band O2 sensors can only give a signal indicating whether the vehicle is above or below the ideal 14.7:1 air/fuel ratio, wide-band sensors are designed to accurately detect readings from 7:1 to 22:1.
Wide-band sensors use an integrated gas pump to stabilize the signal, allowing the sensor to work in temperature ranges far above and below those in which narrow-bands can function.
Because the wide-band signal is stabilized, it can tell the tuner if the air/fuel ratio is 12.25:1 or 15.2:1. A narrow-band sensor can indicate if the mixture is above or below 14.7:1, but not how far off it is.