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How to Test a Bad O2 Sensor with a Scanner?

OBD2 tests bad O2 Sensor
OBD2 tests bad O2 Sensor.
Credit: OBD Focus.

The bad O2 sensor is not good news for a vehicle owner. However, to know How to Test a Bad O2 Sensor with a Scanner, you first need to understand what O2 sensor it, and what does it do.

You will find the O2 sensor mounted in the manifold of the vehicle’s exhaust. They work by generating a voltage when heated. The bulb of the sensor has two surfaces that work as electrodes to create a voltage difference.

What Does an O2 Sensor Do?

Almost every car manufactured since 1980 contains a sensor that lets you check the air/oil ratio. It works to compare the amount of oxygen present in the exhaust and air as it leaves the engine. In case there is a malfunction, it indicates this by flashing a bright orange ‘check engine’ light.

By sensing the oxygen percentage leaving the exhaust, it can send signals to the engine control unit (ECU). Many people have the wrong concept of the measuring process. Thus, it should be noted that it is not the concentration of oxygen, but rather the difference between oxygen present in the air and oxygen from the exhaust gas that has to be taken into account.

Both, too little or too much oxygen, are signs of danger. It does not only pose a threat to your vehicle’s functioning and efficiency but also proves to be hazardous for the environment due to its pollution factor.

Types of O2 Sensor

O2 Sensor
Oxygen Sensor.
Credit: OBD Focus

Depending upon the models, O2 sensors are available in two types.

  • Heated
  • Unheated

Found mostly in old models, unheated sensors need frequent replacements. Whereas, heated oxygen sensors are commonly present in modern vehicles as they tend to be more durable.

Besides this, you can further categorize O2 sensors into several more types.

  • Titania oxygen sensors
  • Zirconia oxygen sensors
  • Wide-band oxygen sensors

Titania sensors are present in a small fraction of car models. However, they work differently because instead of producing voltage they lower the resistance.

The most common, Zirconia O2 sensors come in both, unheated and heated types. The latest cars make use of wide-band O2 sensors which tends to generate a higher level of voltage. Therfore, it is significant to know fully about the type of sensor installed in your car so you can have a close look at the functioning.

What Causes an Oxygen Sensor to Fail?

The failure rate of oxygen sensors is fairly high as they are the sensors that have to be replaced often. Sensors can fail due to a variety of contaminants that make their way through the exhaust. For example, this can include silicates from leaky coolants or phosphorus leading from excessive consumption of oil.

As you read ahead, we will discuss a couple of drawbacks that stem from a bad O2 sensor. Moreover, we will also offer you a step by step guide on how to test oxygen sensors with a scanner. As a driver, it is crucial to know about this topic to understand your vehicle’s working better.

Bad O2 Sensor Symptoms

You will be able to notice several signs and symptoms in case your O2 sensor is failing in giving optimal performance. Listed below are the signs you may come across.

Foul Odor

One of the first symptoms that indicates a bad oxygen sensor is a foul-smelling and strong order that will come from the exhaust. Many times the smell is similar to that of a rotten egg. If not taken care of immediately, this unpleasant odor can also spread to the interiors.

Check Engine Light

As described earlier, this orange flashing light might be the first symptom you notice. However, a bad O2 sensor is not always the issue when this light shows up.

Engine’s Efficiency

Your engine’s competency and efficiency are greatly compromised if there is a bad O2 sensor installed in your exhaust. You may encounter cases of weak acceleration. Furthermore, your engine might also make a rough sound as its performance is hampered.

Fuel Consumption

Do you have to get your tank filled more often than before? This is due to the bad oxygen sensor adversely affecting your vehicle’s fuel consumption. The composition of air and fuel will be rich in case your oxygen sensor doesn’t perform well.

More gas is burnt if the composition is rich during internal combustion. Thus, you will experience poor gas mileage.

Emission Test Failure

Bad oxygen sensors lead to failed emission tests in most cases. Exhaust emissions tend to reach adverse limits. Moreover, your catalytic converter might also fail which leads to pollution, ultimately causing environmental issues.

When to Replace O2 Sensors?

Every O2 sensor has a natural tendency to decrease in functioning as the mileage increases. Therefore, if you own a car of an older model, it is best to replace the oxygen sensor when you drive past the 60,000 to 90,000 miles mark.

As soon as you notice that your car’s engine is stalling or showing jerky movements even when idle, it is time to replace the sensors. Besides this, if your vehicle displays the orange Check Engine light or gives off a really unpleasant smell, then you might want to check your sensor again.

How to Test a Bad O2 Sensor with an OBD2 Scanner?

OBD2 Testing Oxygen Sensor
OBD2 Scanners.
Credit: OBD Focus.

The following steps will help to guide you on how to test the O2 sensor with scanners:

  • First, you have to enter the OBD2 scan tool connector on your car to the diagnostic link connector.
  • Next, you will turn your vehicle on, so that the OBD2 scanner can connect with the car’s onboard system.
  • As the scanner boots, you will select the menu and go to ‘Trouble Code’ or ‘Codes’. These codes are listed below in the table.
P0030Heated Oxygen Sensor (H02S) Heater Control Circuit Bank 1 Sensor 1
P0031Heated Oxygen Sensor (HO2S) Heater Circuit Low Voltage Bank 1 Sensor 1
P0037Heated Oxygen Sensor (HO2S) Heater Circuit Low Voltage Bank 1 Sensor 2
P0130O2 Sensor Circuit Malfunction (Bank 1 Sensor 1)
P0132O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)
P0133O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
P0134O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)
P0135O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

  • After this, you can pick the system you wish to troubleshoot. More than two codes will show up on your screen after this step.  The codes that you see might be active or pending codes.
  • Finally, you can interpret this code. The OBD2 scanning tool will direct you to the problem and display code for it. You can translate this code or just search it on the internet.


Here are some commonly asked questions about O2 sensors.

How Can I Test My Oxygen Sensor?

You can test it by using the OBD2 scanner mentioned above.

Check Engine Light on: What should I do?

This is a sign that you have a bad O2 sensor therefore, a replacement has to be done.

What Type of Sensor Will Suit the Model of My Car Best?

There are three to choose from. You can pick anyone depending on the model of your car.

When Do I Know That My Sensor Needs a Replacement?

There are certain symptoms that your vehicle will start showing in case you have a bad O2 sensor. These include a bad odor, check engine light, hampered vehicle movement, and increased fuel consumption.

What Do the Codes on the OBD2 Tool Mean?

The codes tell the mechanic about the problem with the OBD2 system. If there is a problem with the O2 sensor, the OBD2 tool has a specific code for it.

Final Words

Mentioned above is a guide on how you can use an OBD2 scanner to test for a bad O2 sensor. We have provided the necessary details you need to know for firstly, detecting the issue.

Secondly, the article also contains instructions that will take you step by step through the testing procedure. However, make sure to replace bad O2 sensors to do a favor to your vehicle as well as the environment.

How Oxygen Sensor Works.
Credit: youtube.com

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