Basics

In modern computer contolled engines, an oxgen sensor in the intake, and exhaust (post engine, and often post scrubbers/catalitic converters etc) to give feedback data on the fuel to air ratio
This is useful for efficiency, but is also critical for the operation of a tri-action catalytic converter, as the ratio must be switched between rich, and standard to cycle between chemical reaction "modes"
A narrowband sensor can measure only between approximately 14.0/15.0:1 air/fuel ratios
A Wideband sensor can measure between 12:1 to as lean as 22:1
Also the wideband may start up faster
Operating Temperature Difference:
- From the article "One of the main reasons manufacturers are going to wideband AFR sensors is because the heater channel comes up to operating temperature quicker — as fast as 10 seconds, in some cases. However, wideband sensors also need to be heated to higher operating temperatures to function effectively. While a narrowband sensor operates in the 600° F range, a wideband sensor needs to be heated to 1,200-1,400° F. The fast heating helps reduce emissions during cold starts and allows for improved fuel efficiency because the engine spends less time operating in open-loop mode. Some hybrids use the electrical circuit when the vehicle is in EV mode to heat the AFR sensors before the engine is called to duty, allowing 100 percent closed-loop operation"

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