Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside 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 Sensor Heater Or Heater Circuit

With ignition on and engine off, sensor 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 sensor 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 sensor.

• Intermittent Test

Using scan tester, monitor sensor signal voltage while moving related connectors and wiring harness with engine running at part throttle in closed loop. If failure is induced, sensor signal voltage reading will change from normal fluctuating voltage (greater than .6 volt and less than .30 volt) to a fixed value of about .45 volt. This may assist in isolating location of malfunction.