Oxygen Sensor: Testing and Inspection

Oxygen Sensor Circuit:

FAULT INDICATIONS (CODE 2-1-2)
A fault code is stored if the oxygen sensor signal is:
^ Constantly below .09 VDC or above 1.1 VDC.
^ Varies from its mid-point value (.5 VDC) for 3 minutes after engine temperature exceeds 75° C and a programmed load threshold is maintained.

CHECK VOLTAGE TO OXYGEN SENSOR
1. With engine running, check voltage between oxygen sensor terminal 2 (+) and terminal 1 (-).
2. Voltmeter should indicate battery voltage.
3. If no voltage is present, check fuse #30.
4. If voltage is present, check sensor heater resistance.

CHECK SENSOR HEATER RESISTANCE
1. With ignition "OFF", check resistance between oxygen sensor terminals 1 and 2.
2. Ohmmeter should indicate 3 - 13 Ohms depending on resistor temperature.
3. If resistance is not as specified, replace the sensor.
4. If resistance is correct, remove oxygen sensor and inspect for physical damage.