TESTING

Sensor Output Voltage

NOTE: If equipped with a heated element oxygen sensor (more than one wire connection), perform the Heater Element Resistance test first, as it requires a specific temperature. Performing the output voltage test first will require you to wait for the engine to almost completely cool down.

1. Start the engine and bring to normal operating temperature.
2. Detach the oxygen sensor connector.

   Fig. 1: Measure the single wire sensors by grounding one terminal of the voltmeter and reading the sensor terminal with the engine running

   Fig. 2: Oxygen sensor terminal identification for 3-wire sensors. If only one three wire sensor is used, the FRONT (LH) diagram should be used

   Fig. 3: Oxygen sensor connections for the 4-wire sensors

3. On single wire connectors, measure the voltage between the oxygen sensor wire and ground.
4. On three wire connectors, measure the voltage between the oxygen sensor wire terminal A and ground.
5. On four wire connectors, measure the voltage between the oxygen sensor wire terminal A and terminal B.
6. When the engine speed is increased, the voltage should be 0.5–1.0 volts. When decreasing engine speed, the voltage should drop to 0–0.4 volts.

   NOTE: Voltage that remains above 0.55 volts indicates a continuously rich condition while below 0.55 volts indicates a continuously lean condition. Rich or lean conditions could be an indication of another problem.

7. If the voltage readings are not as specified, replace the oxygen sensor.

Heater Element Resistance

NOTE: This procedure does not apply to single wire sensors.

1. Detach the oxygen sensor connector.
2. On three wire connectors, measure the resistance between terminals B and C.
3. On four wire connectors, measure the resistance between terminals C and D.
4. On all sensors except four wire front sensors, the resistance should read approximately 6 ohms at 68°F (20°C).
5. On four wire front sensors, the resistance should read approximately 13 ohms at 68°F (20°C).

   NOTE: If the sensor readings are out of range, double check the temperature of the sensor. If the temperature is too hot or cold, it may influence an inaccurate reading. If possible, adjust the temperature of the sensor to the proper specification and re-check it.

6. If the readings are not within range, replace the oxygen sensor.