Oxygen Sensor: Testing and Inspection

Bank 1 (Left) Oxygen Sensor Circuit Diagram:

Bank 2 (Right) Front Oxygen Sensor Circuit Diagram:

Bank 2 (Right) Rear Oxygen Sensor Circuit Diagram:

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)

NOTE: Leave the electrical connection between the Engine Computer and the Oxygen sensor intact. Use of a test lead at the oxygen sensor connector is recommended.

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 Computerized Engine Control 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 electrical connectors. Clear all codes set and retrain idle.

8. When two oxygen sensors are utilized, test one and repeat procedure for the other oxygen sensor.

DIAGNOSTIC AID:
If voltage is fixed at greater than 0.6 volts, a rich condition or contaminated sensor is indicated. Make sure system is operating in "Closed Loop" and check for Diagnostic Trouble Codes. Codes 45 &/or 65 should be present. Check for excessive fuel system pressure and perform injector ballance test.

If voltage is fixed below 0.3 volts, a lean condition, grounded or open oxygen sensor circuit, exhaust manifold leak, or AIR system malfunction is indicated. Make sure system is operating in "Closed Loop" and check for Diagnostic Trouble Codes. Codes 44, 63, 64, &/or 13 should be present.

NOTE: Remember, the oxygen sensor only senses oxygen in the exhaust. If there is an exhaust leak at the manifold, or a cylinder misfiring, whether the misfire is due to lack of fuel, lack of spark, or excessive fuel, there will be additional oxygen in the exhaust. This may cause the O2 sensor signal voltage to be low, and all the cylinders except the one(s) misfiring may be operating excessively rich while the system tries to compensate for a "false" lean condition.