Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:
- Poor Connection Or Damaged Harness:
Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. - Faulty HO2S Heater Or Heater Circuit:
With ignition on and engine off, HO2S voltage displayed on Tech 1 should gradually decrease to less than .25 volt, indicating heater is functioning properly. If display does not read as specified, disconnect HO2S and connect test light between terminals "C" and "D". If test light does not light, repair open in suspect wire. If test light lights, replace HO2S. - Intermittent Test:
Using Tech 1, monitor HO2S signal voltage while moving related connectors and wiring harness with engine running at part throttle in closed loop. If failure is induced, HO2S signal voltage reading will change from normal fluctuating voltage (greater than .6 volt and less than .30 volt) to a fixed value of approximately .45 volt. This may assist in isolating the location of the malfunction.