The oxygen sensor in your vehicle plays a vital role in the engine's efficiency. The O2 sensor works to measure the amount of oxygen entering the engine. This information is then used to regulate and maintain the proper air to fuel ratio. The sensor has a voltage resistance that can be tested to ensure it works properly. You can test the sensor while installed in the vehicle. If you have already taken the sensor out to replace or clean it, you can test it with a few tools before putting it back into the vehicle.
Turn the engine off and allow the engine and sensors to cool down for a half hour. Open the bonnet of the vehicle.
Locate the oxygen sensor. The oxygen sensor will be mounted on the catalytic converter or intake manifold. The location will vary based on manufacturer; refer to your repair manual for exact location and a detailed diagram.
Unclip the wire harness on the side of the sensor. Pull on the base of the wire harness to remove. Depending on the manufacturer, there may be two tabs on the side of the harness; if so, depress the tabs and pull the harness out of the sensor.
Remove the screws that secure the sensor in place with the appropriate screwdriver. Lift the sensor off the mount and place it on the workbench face up. This will ensure the sensor does not get damaged.
Clip the ohmmeter's positive lead to the sensor signal lead. The signal lead is the middle of the three wire terminals. Clip the negative lead to a grounded point. Turn the ohmmeter on and read the measurement. When the oxygen sensor is not heated, you should see an infinite reading.
Turn the blowtorch on and point it at the sensor from about 6 inches away. This will allow the torch to change the oxygen in the environment without harming the sensor. The ohmmeter should jump to a reading of about 1 volt for a good sensor. If the ohmmeter does not register, then the sensor is faulty.