How to Test an O2 Sensor with a Multimeter (Step–by–Step Guide)

The O2 sensor aka the oxygen sensor is a small device with a sensor tip that is put into the exhaust pipe for the sole purpose of measuring the oxygen ratio in the exhaust emissions. Its main role is to bring down the number of harmful gases being released into the environment and that is done by measuring the number of unburned oxygen exiting the system. If it turns out the fuel mixture has little or excess oxygen, the engine burns lean and this data is important to the control unit system (ECU) in controlling the fuel-oxygen ratio.

In general, if you want to know how to test the O2 sensor with Multimeter then all you need to do is 1. Check the heating element which is done by turning on the Multimeter and setting it to resistance mode, 2. Connect the test leads to the heater power and ground connector pins or wires, and 3. read the Multimeter measurement of the oxygen sensor.

To Test Oxygen Sensor

When trying to test an oxygen sensor it is always a good idea to know the type of oxygen sensor in your car. The most common ones found have between one and five wires linking them to the rest of the vehicle and a good thing to do is to identify the type before you start testing it. 

Wideband Zirconia sensors which are mostly called wide-band sensors are among the most common sensors and they have four electronic connections among which one pair of the connections is their output signal.

  • The most common types of oxygen sensors are the zirconia sensors which are also known as narrowband oxygen sensors and have two electrodes that have an output of 200mV in a lean condition and an output of 800mv in a rich condition. In normally functioning engines their output is 450mv.

O2 sensor diagram circuit

The location of the oxygen sensor is also extremely important and it can be found in one of two spots along with the engine exhaust the first location is between the exhaust manifold and the catalytic converter and the second location is between the catalytic converter and the exhaust outlet (tailpipe).

Heater Wire vs Signal Wire Test

Heater Wire Test

  • Check the engine to make sure it is switched off.
  • Switch the digital Multimeter to the Ohmmeter setting.
  • The next step is for you to back probe the oxygen sensor heater’s hot and ground wire.
  • Perform Multimeter connections of the red lead of the digital Multimeter to the heater hot wire and the black lead of the digital Multimeter to the heater ground wire.
  • The final step is to check whether you have good sensors which will be known if the readings of the Multimeter are between 10 ohms to 20 ohms.

engine and multimeter

Signal Wire Test

If you want to know how to check O2 sensors with a Multimeter using a signal wires test then what you need to do is as follows:

  • Check the engine to make sure it has cooled down.
  • Switch the digital Multimeter to the voltmeter setting.
  • Then you need to back probe the oxygen sensor’s signal voltage and ground wire.
  • Perform Multimeter connection of the black lead of the digital Multimeter to the back probed ground signal wire and the red lead of the digital Multimeter to the sensor signal voltage wire.
  • Turn on the engine of the car.
  • The voltmeter should display a reading between 0.1 to 0.9 if the sensor wires of your car are working properly and are in good condition.

You should note that if any of your readings using heater wires or signal wires are not similar to the readings above then you have bad sensors and you should get the oxygen sensors diagnosed and repaired because bad sensors are not good for the fuel ratio of the combustion chamber of your car. (1)

Why a Multimeter is Best if the Scan Tool Fails

The scan tool is useful in showing you the performance of your O2 upstream sensor and it is done by running your engine at 2,000 RPM and observing the oxygen sensor voltage. If the O2 sensor is in good condition then the sensor will react to the oxygen content and change volts quickly. The steps for using a scan tool are as follows: –

  • You need to connect your scan tool and then start the engine.
  • Next, you open the engine at fast idle (2,500) for two minutes which will allow the oxygen sensor to adjust and warm up to its operating temperature.
  • The next thing is to make sure your car is in closed-loop operation by taking a look at the activity in the scan tool
  • Choose the “snapshot” mode in your scan tool
  • Hold the engine at a steady speed.
  • Start recording the sensor output
  • Check the snapshot and place a marker beside each oxygen sensor voltage range and the readings should be (0 to 300mV and 600 to 1000mV) for both ends. If the readings of the sensor output somehow appear in the middle, then the upstream O2 sensor is faulty.

After these various steps if the scan tool fails then the best option is a Multimeter which will be able to help you test both upstream and downstream oxygen sensors in an efficient and precise manner.

Testing the O2 Sensor

There are certain steps you need to be aware of if you want to know how to test oxygen sensor with Multimeter and these steps are as follows:

  • Locate the specific oxygen sensor that requires on the O2 test
  • You will also need to use a Multimeter to test the oxygen sensor
  • Turn on the car and allow it to warm up till it reaches a perfect operating temperature which could be around 20 minutes for you to obtain the optimal temperature.
  • Turn off the engine after getting the desired temperature.
  • Connect the red cable to the oxygen sensor’s signal wire and the black cable to a suitable ground.
  • Perform the actual test by switching on your car and observing the Multimeter readings these readings should range between 100mV to 900mV which will ascertain that the lambda sensor is operating normally and you can stop the test here. However, if the readings are not within this range, then the lambda sensor has a definite problem.
  • Test the oxygen sensor to see how it responds to the consumption of fuel. (2)
  • Disconnect the hose from the PVS (positive crankcase ventilation) valve at the valve cover which will permit entry of a significant amount of air into the engine so the Multimeter will read about 200mV and if the oxygen sensor fails to detect then it is faulty.
  • Connect the PVC hose back.
  • Test the oxygen sensor’s response against a scenario where fuel consumption is significantly high.
  • Read the Multimeter and the supposed reading should be around 700mV or 800mV because of the reduction of the supply of oxygen to the engine and if the readings appear differently, then the O2 sensor is faulty and needs replacement.
  • Connect the hose back to the air cleaner.

Wrapping Up

There are certain signs which will tell you if there is something wrong with your oxygen sensor wires and these could be a reduction in gas mileage, bad odor from the exhaust pipe, the starter getting hard, engine light turning on and the car engine can make a rough idling. That is why it is important to know how to test an oxygen sensor with a multimeter because after testing you will know whether you have a bad sensor or a good sensor that you can fix immediately.

Before you go, you may want to check the list below of other multimeter learning guides. Until our next article!






References
(1) combustion – https://www.britannica.com/science/combustion
(2) consumption of fuel – https://www.sciencedirect.com/topics/materials-science/fuel-consumption

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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gI realized early on carpentry was a huge passion for me and I’ve stayed in the industry for over 20 years now. This gives me a unique ability to really be able to tell you what the best tools and recommendations are. I’m not only a carpenter but I also like machinery and anything to do with electrics. One of my career paths starting off was as an apprentice electrician so I also have a lot of experience with electrical products and anything related.