Oxygen Sensor: Testing and Inspection
SENSOR FUNCTIONAL TEST
NOTE: This test should be performed only after basic inspection, and ignition and fuel systems inspections are passed.
NOTE: Only use a high input impedance Digital Volt Ohm Meter (DVOM) when testing components on computerized vehicles.
CAUTION: verify voltmeter is set to read VOLTS only (not ohms). Verify external voltage is not applied to the sensor lead, as damage to the sensor may occur.
1. Make sure the vehicle is at normal operating temperature. Run the engine at 2500 rpm for 3 minutes with the transmission in PARK (A/T) or NEUTRAL (M/T).
2. With engine OFF, connect the negative lead of the DVOM to engine ground. Set the DVOM to read DC VOLTS. Disconnect the oxygen sensor connector. Connect the positive lead of the DVOM to the oxygen sensor.
3. Create a full lean condition, by removing a large vacuum hose, for 10 seconds. Voltage should decrease to 0.2 volt or less and remain there.
4. Create a full rich condition, by introducing propane into intake manifold, for 10 seconds. Voltage should increase to 0.8 volt or less and remain there.
5. Verify that engine is at operating temperature and O2 sensor heating element (if equipped) is functioning. See, sensor heating element test.
6. If engine is at operating temperature and heating element passes, but the sensor fails to vary according to the test steps above, the sensor is defective.
7. Connect the oxygen sensor and clear codes.
SENSOR HEATING ELEMENT TEST
NOTE: This test should be performed only after basic inspection, and ignition and fuel systems inspections are passed.
NOTE: Only use a high input impedance Digital Volt Ohm Meter (DVOM) when testing components on computerized vehicles.
1. Disconnect the oxygen sensor(s) electrical connector from the wiring harness
2. Connect DVOM across terminals 3 and 4 of the sensors electrical connector. Set to read OHMS.
3. Resistance value should be between 5 and 7 ohms.
4. Replace the sensor if the resistance reading is not within the previous specifications or if the ohmmeter indicates infinite resistance.
ENGINE CONTROLLER RESPONSE TEST
NOTE: A four gas analyzer will be needed to perform this test.
NOTE: This test should be performed only after sensor functional test, and sensor heating element tests are passed.
NOTE: When performing this test it is important that no part of your body contact the vehicle body, as inaccurate test results may result.
CAUTION: NEVER apply voltage directly to any computer sensor wire.
1. Make sure the vehicle is at normal operating temperature. Run the engine at 2500 rpm for 3 minutes with the transmission in PARK (A/T) or NEUTRAL (M/T).
2. With engine OFF, disconnect oxygen sensor connector and connect a jumper lead to the computers oxygen sensor return wire, terminal 2 of the electrical connector.
3. Start engine and run at 2500 rpm for 1 minute with the transmission in PARK (A/T) or NEUTRAL (M/T).
4. Let engine idle.
5. Simulate a lean command (rich condition), by touching one hand to jumper wire and other hand to battery negative, for 10 to 20 seconds. HC and O2 readings should begin to increase.
6. Simulate a rich command (lean condition), by touching one hand to jumper wire and other hand to battery positive, for 10 to 20 seconds. HC and O2 readings should begin to decrease, and CO should begin to increase.
7. If computer system fails to respond to these artificial commands, further testing of the oxygen sensor circuit and/or computerized engine control system will be necessary.