Circuit Description

PCM monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. PCM determines if HO2S is functioning properly by counting number of times signal voltage crosses the rich-to-lean and lean-to-rich thresholds. A lean-to-rich condition is when voltage changes from less than 300 mV to greater than 600 mV. A rich-to-lean condition is when voltage changes from greater than 600 mV to less than 300 mV.

DTC will run if no active fuel trim, injector, misfire, AIR, CKP, ECT, EGR, EVAP, IAT, MAF, MAP, or TP sensor DTCs are present, DTC P0131, P0132 or P0135 not set, system voltage is greater than 9 volts, system is in closed-loop, engine running for at least 3 minutes, ECT greater than 167°F (75°C), engine speed greater 1000-3000 RPM, MAF 15-40 gm/s and these conditions are stable for 3 seconds.

DTC will set when PCM monitors HO2S switches fewer than 5 rich-to-lean and lean-to-rich condition.