Theory Of Operation

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The Powertrain Control Module (PCM) uses a Fuel Mass Observer (FMO) Monitor to check the injection correction quantity for exceeding permissible limits and the fuel mass over a period of time. The FMO activation time monitor checks time to enter closed loop air/fuel ratio control diagnosis.

This is a 5-wire Wideband O2 Sensor. This sensor operates differently from traditional O2 Sensors. The wide-band O2 Sensor tip consists of two cells that provide different functions, a measurement chamber and a detection chamber with pumping capabilities. The oxygen pumping function is the ability to pump oxygen into or out of the measurement chamber depending on the level of oxygen in the measurement chamber. This function provides the wide-band sensing capabilities and is critical for proper oxygen measurement. The controller keeps adjusting the O2 Sensor model until it follows the measured O2 signal (the difference converges to zero).

The described rationality check will detect fuel injection quantity that is too rich, and excessive time to enter closed loop air/fuel ratio control failure.