AFR sensor
The AFR sensor is an air-fuel ratio sensor that is slowly replacing (or supplementing) the zirconia oxygen sensor (O2 sensor) in modern motor vehicles.
Background
Zirconia oxygen sensor
The early introduction of the oxygen sensor came about in the late 1970s. Since then zirconia has been the material of choice for its construction. The zirconia O2 sensor produces its own voltage, which makes it a type of generator. The varying voltage will display on a scope as a waveform somewhat resembling a sine wave when in closed loop control. The actual voltage that is generated is a measure of the oxygen that is needed to complete the combustion of the CO and HC present at the sensor tip. The stoichiometric air-fuel ratio mixture ratio for gasoline engine is the theoretical air-fuel ratio at which all of the fuel will react with all of the available oxygen resulting in complete combustion. At or near this ratio, the combustion process produces the best balance between power and low emissions. At the stoichiometric air-fuel ratio, the generated O2 sensor voltage is about 450 mV. The Engine Control Module (ECM) recognizes a rich condition above the 450 mV level, and a lean condition below it, but does not detect the extent of the richness or leanness. It is for this reason that the zirconia O2 sensor is called a “narrow-band” O2 sensor.
