2002 MY OBD-II System Operation Summary - MotorCraftService.com

Rear HO2S SignalA 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. Most 2002 MY vehicle will monitor the rear HO2S signal for high voltage, in excess of 1.5volts and store a unique DTC. (P0138 P0158). An over voltage condition is caused by a HO2S heater or batterypower short to the HO2S signal line.Rear HO2S Check Operation:DTCs P0136 No activity, Bank 1P0138 Over voltage, Bank 1P0156 No activity, Bank 2P0158 Over voltage, Bank 2Monitor executiononce per driving cycle for activity test, continuous for over voltage testMonitor SequencenoneSensors OKMonitoring Durationcontinuous until monitor completedTypical Rear HO2S check entry conditions:Entry condition Minimum MaximumInferred exhaust temperature range 400 o F 1400 o FRear HO2S heater-on timeThrottle position120 secondspart throttleEngine RPM (forced excursion only) 1000 rpm 2000 rpmTypical Rear HO2S check malfunction thresholds:Does not exceed rich and lean threshold envelope:Rich < 0.25 to 0.50 voltsLean > 0.40 to 0.65 voltsJ1979 Mode $06 DataTest ID Comp ID Description Units$03 $02 Downstream O2 sensor switch-point voltage voltsConversion for Test ID $03: multiply by 0.00098 to get voltsFORD MOTOR COMPANY REVISION DATE: OCTOBER 02, 2001 PAGE 26 OF 66