Oxygen Sensor: Testing and Inspection

Oxygen sensor function test
- Connect exhaust analyzer to the CO test pipe, at the right rear of the engine compartment, to measure the CO % ahead of the catalytic converter.
- Run engine to operating temperature. Engine idle speed must be adjusted correctly.
- Disconnect oxygen sensor at connector.
- Observe and record the CO %.
- Disconnect the vacuum line to the fuel pressure regulator, CO% must change.
- Reconnect vacuum line and CO % must return to previous level.
If CO % changes:
Oxygen sensor is functional.
If CO % does not change:
Bring engine RPM up to 2500 for 1-2 minutes to insure the sensor is at full temperature and retest.
If CO % still does not change:

Fig. 49 Oxygen Sensor Connector Plug:

- Connect a voltmeter between ground and pin connector # 1 of oxygen sensor plug (on sensor side). Voltmeter should reed 0.1 - 1.0 Volts.
If reading is out of the range:
Bring engine RPM up to 2500 for 1-2 minutes to insure the sensor is at full temperature and retest.
If voltage is still not in range:
Replace oxygen sensor and retest.
If voltage is in range:
- Disconnect the vacuum line to the fuel pressure regulator, voltage reading must change.
- Reconnect vacuum line and voltage reading must return to previous level.
If voltage reading does not change:
Replace oxygen sensor and retest.
If voltage reading changes but CO % does not change:

Fig. 49 Oxygen Sensor Connector Plug:

- Connect a jumper wire between ground and pin connector # 1 of oxygen sensor plug (on control unit side), CO % must rise.
If CO % does not change:
- Check wiring to the control unit from the oxygen sensor and check power and grounds for the control unit.

Oxygen Sensor Heater Test
- Connect an ohm meter between pin connector # 2 and # 3. Ohm meter should display some resistance.
If ohm meter measures 0 or infinite resistance:
Heating element is faulty. Replace oxygen sensor and retest.