2005 MY OBD System Operation Summary for Gasoline Engines

$-A functional test of the rear HO2S sensors is done during normal vehicle operation. The peak rich and leanvoltages are continuously monitored. Voltages that exceed the calibratable rich and lean thresholds indicate afunctional sensor. If the voltages have not exceeded the thresholds after a long period of vehicle operation, theair/fuel ratio may be forced rich or lean in an attempt to get the rear sensor to switch. This situation normally occursonly with a green catalyst (< 500 miles). If the sensor does not exceed the rich and lean peak thresholds, amalfunction is indicated.2005 MY vehicles will monitor the rear HO2S signal for high voltage, in excess of 1.1 volts and store a uniqueDTC. (P0138, P0158). An over voltage condition is caused by a HO2S heater or battery power short to the HO2Ssignal line.Some 2005 MY Partial Zero Emission Vehicles (PZEV Focus) will utilize three sets of HO2S sensors. The frontsensors (HO2S11/HO2S21) are the primary fuel control sensors. The next sensors downstream in the exhaust areutilized to monitor the light-off catalyst (HO2S12/HO2S22). The last sensors downstream in the exhaust(HO2S13/Ho2S23) are utilized for very long term fuel trim in order to optimize catalyst efficiency (Fore Aft OxygenSensor Control). Ford's first PZEV vehicle uses a 4-cylinder engine so only the Bank 1 DTCs are utilized.Rear HO2S Check Operation:DTCs Sensor 2P0136 HO2S12 No activity orP2270 HO2S12 Signal Stuck LeanP2271 HO2S12 Signal Stuck RichP0138 HO2S12 Over voltageP0156 HO2S22 No activity orP2272 HO2S22 Signal Stuck LeanP2273 HO2S22 Signal Stuck RichP0158 HO2S22 Over voltageDTCs Sensor 3Monitor executionMonitor SequenceSensors OKMonitoring DurationP2274 HO2S13 Signal Stuck LeanP2275 HO2S13 Signal Stuck RichP0144 HO2S13 Over voltageP2276 HO2S23 Signal Stuck LeanP2277 HO2S23 Signal Stuck RichP0164 HO2S23 Over voltageonce per driving cycle for activity test, continuous for over voltage testnonecontinuous until monitor completedFORD MOTOR COMPANY REVISION DATE: APRIL 28, 2004 PAGE 42 OF 131