How to Tell Which O2 Sensor is Bad? 2 Easy DIY Steps

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Oxygen sensor replacement costs only around $20 to $100, which is reasonably cheap. Routine replacements can help avoid more expensive problems. The O2 sensors, one of the most important car sensors, analyze the mixture of fuel and air in your car’s engine and make any necessary adjustments to the electronic control unit (ECU). 

For anyone who wants to avoid costly, labor-intensive, and time-consuming troubles, identifying if your O2 sensor is bad is essential. But it can get complicated, and if you don’t do it right, you could spend more money repairing your engine’s timing and combustion intervals and causing stalling or slow acceleration.

Here are a few of the most frequent warnings that your oxygen sensor needs to be replaced. We’re going to show you how to identify if your O2 sensor is bad in 5 steps so you can: 

  • Prevent more costly, complicated, and frustrating problems.
  • Avoid stalling or slow acceleration.
  • Maintaining optimum engine performance and combustion intervals.
  • Steer clear off from releasing harmful environmental pollutants.

If you want to save your money, engine performance, and the environment, continue reading this article! 

Importance of O2 Sensor

The amount of unburned oxygen in the exhaust is determined by the O2 sensor. It interacts with your car’s electronic control unit (ECU) to determine the ideal air-to-fuel ratio for optimum engine performance.

It also has the crucial duty of measuring this combination by keeping an eye on these oxygen levels so that the fuel injection system can make the necessary adjustments. 

How to tell which O2 sensor is bad?

Using an OBD-2 scan tool is the simplest approach to determine if your O2 sensors have gone bad. Simply connect the device to it, enter your VIN and other necessary information, check the menu for codes, understand the meaning of the codes, and start the diagnostic.

As an alternative, you may also use a multimeter or a voltmeter, but you will first need to identify the heater’s power and ground connectors, locate the O2 sensor, and cut the cables connecting them.

Step #1: Test the O2 sensor using OBD 2 scan tool

An OBD-2 scan tool is required to examine a car’s O2 sensors. We strongly advise INNOVA 5210. The newest OBD2 Diagnostic Code Scanner for the Innova features a Battery/Charging System Test, can read and erase ABS codes, reset oil light indicators, and provides live data for more precise information.

Additionally, this device includes an easy self-diagnosis of emission status and other important information and a premium OBD2 Code Reader with enhanced coverage and functionality.

Steps in testing O2 sensor using OBD 2 scan tool.

1. Locate your car’s diagnostic link connector (DLC).

Typically, you may locate this triangular-shaped connector under the steering column. If you cannot locate it, read your owner’s handbook or conduct a fast web search to determine what you are searching for.

2. Connect the OBD-II tool to the DLC.

Turn the ignition key once it is completely in but hold off on starting the car. You’ll notice some notifications on the screen when the scan tool begins to communicate with your car’s internal systems. If, for some reason, nothing appears on the screen, check to see if it is fully plugged in.

3. As instructed on the scanning screen, enter the information.

The Vehicle Identification Number (VIN) and other fundamental details about your car may be included in this. There are differences between each OBD-II scan tool in terms of how much data you must input.

4. When the scanner shuts off, check the menu for codes.

The way various scanner types handle this phase differs. While others let you select which codes you wish to view, some just show the problematic codes.

5. Determine the meaning of the codes.

The codes should essentially be the same, even if the displays can be different. Typically, they will begin with the letters P, B, C, or U. (Powertrain, Body, Chassis, and Undefined). The vehicle’s make is indicated by the first number that comes after the letter.

The second number designates the particular component of the car, such as the gearbox. The final two figures represent the precise issue at hand. To obtain the information, you must consult a code chart online.

6. Conduct the diagnosis.

To identify a problem with a car, you need to be somewhat knowledgeable about them. The code will explain what’s wrong, but it won’t always explain how to resolve it. At this point, you have two options: either take your car to a shop with a license to remedy the issue or conduct some independent study to see if you can do it yourself.

Sometimes all it takes to fix the problem is replacing a fuse. Sometimes it could be a little more serious, requiring the skills of someone who is aware of the proper course of action.

7. Check engine light reset.

After your car is serviced, you should be able to drive it for a short period without the check engine light appearing. However, you may use your OBD-II scan equipment to take care of it if you want to get rid of it immediately. Just choose the option to reset the check engine light from the main menu and click it. The light should turn off in a little while, and then you may continue.

Step #2: Test the O2 sensor using a multimeter

Steps in testing O2 sensor using a multimeter. 

  1. Turn on the automobile and let it warm up for as long as it takes to achieve the ideal operating temperature, which might take up to 20 minutes. Once the engine has reached the proper temperature, turn it off.
  1. Connect the black cable to a suitable ground and the red cable to the signal wire of the oxygen sensor.

3. By turning on your automobile and checking the multimeter readings, you may carry out the real test and determine whether the lambda sensor is functioning normally. At this point, the test can be stopped. But if the measurements fall outside of this range, there is unquestionably an issue with the lambda sensor. See how the oxygen sensor reacts to fuel usage by testing it.

4. When the hose is disconnected from the PVS (positive crankcase ventilation) valve at the valve cover, a large amount of air will be allowed to enter the engine, causing the Multimeter to register roughly 200mV. If the oxygen sensor is unable to detect this change, the sensor is malfunctioning. 

5. Reattach the PVC hose.

6. Test the oxygen sensor’s behavior in a situation with excessive fuel usage. Due to the decreased oxygen supply to the engine, the multimeter measurement should be around 700mV or 800mV. If the readings differ, the O2 sensor is defective and must be replaced.

7. Reattach the hose to the air purifier.

Wrapping up

Using an OBD II scan tool simplifies identifying which O2 sensor has failed. The simplest method is to use a multimeter if you don’t have access to any diagnostic tools. This guide has outlined the procedures for determining which O2 sensor is malfunctioning.

Invest in an OBD 2 scan tool (INNOVA 5210) or a multimeter and learn how to use it to avoid paying for expensive diagnostics from repair businesses. In addition to O2, you can use them to diagnose other auto issues, and they offer real-time data for more accurate information.

Now that you know how to identify if your O2 sensors have gone bad, it’s time to know if you can drive your car with a bad O2 sensor. We hope this article helps you, and always remember that prevention is much better than cure, so do your routine O2 sensor checking and replacements to prevent other costly, labor-intensive, and time-consuming engine problems.

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