If it doesn’t, there’s likely something wrong with the O2 sensor. It should read close to 800 mV in response to the reduced oxygen entering the engine. Use a rag to close off the hose connection opening to inhibit airflow to the engine.Detach the plastic hose connection to the air cleaner assembly.Testing the O2 Sensor’s Response to Rich Fuel Consumption If it doesn’t, there’s something wrong with the O2 sensor. It should read around 200 mV to 300 mV in response to the increased air in the engine. Detach the hose from the positive crankcase ventilation (PCV) valve (or another large vacuum hose).Testing the O2 Sensor’s Response to Lean Fuel Consumption Follow these steps to rule out other issues, such as rich and lean condition: Most of the time, these symptoms could also be related to other malfunctions inside your engine. A defective spark plug or an exhaust leak, for example, may cause a consistently low reading.Īlthough a good voltmeter usually provides accurate results, this may require further analysis of other engine components. Just like a false high reading, some situations could also give out a false lean result. If your vehicle’s O2 sensor gives you a voltage reading that is consistently below 350 mV, it may also indicate that something is wrong with your sensors or that the fuel mixture in the system is too lean. A spark plug that is too close to the oxygen sensors.A break contamination of the wirings and its connection.Additives in the engine coolant caused by silicon poisoning.Take note that a high reading could also be a result of other factors, such as:
On the other hand, if the O2 sensor gives out a voltage that is constantly above 550 mV, that means that there is too much fuel mixture or your O2 sensor might be contaminated. If your upstream O2 sensor continuously gives out a voltage that is consistently about 450 mV, this may mean that your oxygen sensor is not responding to the fuel mixture. Here’s a video to give you an idea of how the test is done: On the other hand, the downstream (after the catalytic converter) sensor should produce a fairly steady voltage. Note: Ideally, the voltage readings from the upstream O2 sensors would be continually changing from below 300 mV to above 800 mV because of the effort to control the fuel mixture. This is the point where the air-fuel mixtures are adjusted based on real-time O2 sensor data.
After connecting the leads, start the engine until it’s warmed up and reaches close-loop operation.Take the black lead and connect it to a good ground.Connect the red lead of the voltmeter to the O2 sensor’s signal wire using a back probe test lead. Make sure your engine is switched off.Set your multimeter to the millivolt (mV) DC setting or 2 DC Volts setting.Note: This test is for traditional, zirconia O2 sensors (not wideband air/fuel ratio sensors). How do I test an oxygen sensor through digital voltmeter testing? To do this test, you’re going to need a digital multimeter (DMM). Digital Voltmeter Testing To test an oxygen sensor through digital voltmeter testing, you’ll need a digital multimeter (DMM). Take note that results may vary depending on your car’s year, make, and model. These tests below are only general guidelines.
If you get a code that points to the O2 sensor, such as a P0135 or a P0136, then there may be no need to perform an O2 sensor test. Next, do some research to find out what the code/s mean (take a look at our OBD-II code directory for in-depth guides on codes related to the O2 sensor). These will help you identify the issue that’s affecting your vehicle. But how would you know if it is really one of your O2 sensors that is causing problems? Testing Your Oxygen Sensor: How-To Guideīefore you start testing your O2 sensors, use a code reader or scan tool to get the diagnostic trouble code (or codes). Driving with a faulty O2 sensor may trigger the check engine light, cause performance problems, and eventually damage your catalytic converter.