Oxygen Sensor: Testing and Inspection

Dwell Terminal:

Dwell Method

1. Thoroughly warm up engine. Engine must be operating in closed loop. This test will not be valid if oxygen sensor is too cool.
2. Connect dwell or duty cycle meter to dwell terminal. Use 4 cylinder scale.
3. With engine idling, disconnect oxygen sensor and ground ECM end of terminal.
4. If the meter reading is under 10° after 30 seconds, the indication is bad oxygen sensor connections or a faulty oxygen sensor.
5. If the meter reading is over 10° after 30 seconds, refer to COMPUTERS AND CONTROL SYSTEMS.
6. Clear codes after completing work.

Voltage Measurement Method

Oxygen Sensor Testing:

The output voltage of the oxygen sensor can be checked with a voltmeter having a minimum input impedance of one megohm.

1. Disconnect oxygen sensor from vehicle harness.
2. Install a jumper with exposed wire between sensor and vehicle harness connectors.
3. Set voltmeter at approximately two volt range.
4. Connect positive lead of voltmeter to jumper and negative lead to ground.
5. Start engine and run at fast idle until system goes into closed loop. The meter reading should move between approximately 0.50V and 0.80V.
6. Replace the oxygen sensor if it fails this test.
7. Clear codes after completing work.