OBD Operation Summary for Fiesta - MotorCraftService.com

Catalyst Efficiency MonitorThe Catalyst Efficiency Monitor uses an oxygen sensor after the catalyst to infer the hydrocarbon efficiency based onoxygen storage capacity of the ceria and precious metals in the wash coat. Under normal, closed-loop fuel conditions,high efficiency catalysts have significant oxygen storage. This makes the switching frequency of the rear HO2S veryslow and reduces the amplitude of those. As catalyst efficiency deteriorates due to thermal and/or chemical deterioration,its ability to store oxygen declines and the post-catalyst HO2S signal begins to switch more rapidly with increasingamplitude. The predominant failure mode for high mileage catalysts is chemical deterioration (phosphorus deposition onthe front brick of the catalyst), not thermal deterioration.Integrated Air/Fuel MethodThe Integrated Air/Fuel Catalyst Monitor assesses the oxygen storage capacity of a catalyst after a fuel cut event. Themonitor integrates how much excess fuel is needed to drive the monitored catalyst to a rich condition starting from anoxygen-saturated, lean condition. Therefore, the monitor is a measure of how much fuel is required to force catalystbreakthrough from lean to rich. To accomplish this, the monitor runs during fuel reactivation following a Decel Fuel ShutOff (DFSO) event. The monitor completes after a calibrated number of DFSO monitoring events have occurred. The IAFcatalyst monitor can be used with either a wide range O2 sensor (UEGO) or a conventional switching sensor (HEGO).Functionally, the equation is:⎛ Fuel _ needed _ for _ stoich⎞IAF = ∫⎜− Fuel _ needed _ for _ stoich ⎟⎝ Fuel _ Measured⎠where the units are in pounds mass of fuel.The monitor runs during reactivation fueling following an injector cut. The diagram below shows examples of one DFSOevent with a threshold catalyst and with a Full Useful Life catalyst where:ooooVoltage / INJONINJON = # of injectors on.CMS is the catalyst monitor sensor voltage. When the rear O2 sensor crosses 0.45 volts (i.e. rich) the monitorwill complete for the given DFSO event.2.51.50.5LAM (LAMBDA) is the front O2 sensor (UEGO) signal.CATMN_IAF_SUM is the integral from the equations above (Y axis on the right).321Threshold Catalyst - IAF Catalyst Monitor Integration CATMN_IAF_SUMINJONCMSLAMCATMN_IAF_SUM000 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Time (sec)0.020.0180.0160.0140.0120.010.0080.0060.0040.002Fuel (lbm)CONTINENTAL REVISED: SEPTEMBER 17, 2010 PAGE 4 OF 111