Fuel Mass Observer
WARNING: This page is about a different car, the 2013 Ford F-550 Super Duty, 2013 Ford F-450 Super Duty, 2013 Ford F-350 Super Duty, and 2013 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
The fuel mass observer is an algorithm used to detect deviations in performance of all fuel injectors from nominal. The oxygen percentage as measured by the nitrogen oxides bank 1, sensor 2 (NOx12) sensor is compared to a modeled oxygen percentage based upon the current fuel, boost, and EGR settings. The deviation between the observed and modeled oxygen percentage is expressed in terms of the error in fueling required to explain the deviation. This calculated error in fueling is then divided by the current requested fueling level to generate a ratio of percentage error in fueling. This fueling ratio is then filtered over time. If the filtered error in fueling ratio exceeds minimum or maximum limits, then a DTC is set.