Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

To diagnose a faulty HO2S heater or heater circuit. After a cool down period, turn ignition on, engine not running. Use scan tool to observe HO2S voltage. HO2S voltage should gradually drop to about 250 millivolts. If parameter does not display as specified, turn ignition off and disconnect suspect HO2S 4-pin harness connector. Connect test light between ignition feed (Red/White wire) and heater ground circuit (Black wire). See WIRING DIAGRAMS article. Turn ignition on. Test light should illuminate. If test light does not illuminate, repair open in ignition feed or ground. If test light illuminates, replace suspect HO2S.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage to a fixed voltage. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.