Note. For circuit reference, see WIRING DIAGRAMS article.
Circuit Description
PCM supplies a bias voltage of about 450 mV between the HO2S signal and low circuits. When measured with a 10 megohm DVOM, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. If HO2S 1 voltage remains at or about the 450 mV bias for an extended period of time, DTC will be set, indicating an open sensor signal or sensor low circuit.
For duplication of DTC, ensure no active misfire, fuel injector circuit, EVAP, TP, IAT, MAP, ECT, MAF, or AIR DTCs are set, engine running longer than 200 seconds, system voltage at 9-18 volts and ECT at greater than 122°F (50°C).