Oxygen Sensor: Testing and Inspection

A fault code is stored if the oxygen sensor signal (or associated wiring), is out of range rich or lean.

CHECK OXYGEN SENSOR SIGNAL
1. Start engine and warm to operating temperature.
2. Fold back sensor lead boot at oxygen sensor.
3. Connect voltmeter between sensor lead and ground. Voltmeter should oscillate between 0.1 and 0.9 VDC.
4. If reading is fixed at 0.4 - 0.6 VDC, check for open circuit between sensor and engine control module.
5. If reading is too low, check for grounded signal wire, intake leak, or heater element operation.
6. If reading is too high, check for signal lead short to other wiring.
7. If wiring is OK, replace sensor and recheck.

CHECK HEATER ELEMENT VOLTAGE SUPPLY
1. With engine running, check voltage between oxygen sensor (+) terminal U/R (blue / red) and ground.
2. Voltmeter should indicate battery voltage.
3. If no voltage is present, check U/R lead between fuel pump relay terminal 87 and sensor connector terminal.

CHECK SENSOR HEATER RESISTANCE
1. With ignition "OFF", check resistance between oxygen sensor wires U/R and B (black).
2. Ohmmeter should indicate approximately 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.