Oxygen Sensor: Testing and Inspection

VISUAL INSPECTION:
^ Connectors and wires
^ Housing and insulator for cracks/damage
^ Sensor tip for silicone contamination (white powdery coating)

PERFORMANCE TEST: Checks working range and response (speed).
1. Warm engine
2. Install DVOM between sensor and ground (2 volt D.C. range)
3. "RUN" engine at steady cruise speed (about 2500 rpm)
Voltage should vary at least eight times in ten seconds between 0.2 and 0.8 volts (normal range).
4. Drive system rich: The use of a properly adjusted propane flow-meter (J-26911) is industry standard.
Voltage should increase to at least 0.8 volts within two to three seconds.
5. Drive system lean: Create a vacuum leak from a source that is not an PCM input or output.
Voltage should drop to at least 0.3 volts within two to three seconds.

NOTE: After each test the O2 sensor should return to normal operating range within two to three seconds.

6. O2 Sensor should be replaced for failure to pass any of the tests above.

NOTE: A CEC system that is operating excessively rich or lean will drive the 02 sensor to its maximum range and should be repaired first and not diagnosed as a 02 sensor failure.

7. Reconnect all hoses and electrical connectors. Clear all codes set and retrain idle.


Remember, the oxygen sensor senses the presence of oxygen in the exhaust. If air is entering the exhaust system from outside, the sensor signal will show a false lean condition (voltage below 0.3 volts and constant) and the engine may actually be running extremely rich. Also, if the sensor is contaminated, the signal may show a false rich condition (voltage greater than 0.8 volts and constant), forcing the engine to run lean.