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Smart Vehicle Health Monitor Mini

Oxygen Sensor: All You Need To Know

A car requires gasoline to run, but it also needs oxygen. Your vehicle requires oxygen to create the spark to ignite the engine and burn the gasoline which will create the fuel needed. Most cars require a ratio of 14 grams of oxygen for every gram of gas. How do you know if you have the correct balance to keep your vehicle running efficiently?


How Does The Oxygen Sensor Work?

An Oxygen sensor is generally mounted in the exhaust stream of vehicles to measure the oxygen content of the exhaust gases. The sensor will compare the oxygen content to the oxygen proportion in the air and passes that information back to your vehicle’s engine computer (yes, your car has a computer), called Engine Control Module(ECU). A properly functioning Oxygen sensor will help your car to not only pass an emissions test but will also help your car’s fuel efficiency.

Newer vehicles will have multiple sensors to provide the engine computer with two readings and more data. Basically, there are upstream and downstream Oxygen Sensors before and after the catalytic converter in the exhaust pipe, also called Sensor 1 and Sensor 2.

  1. The upstream O2 sensor monitors the burning efficiency of the engine and sends back the data to ECU, which will calculate the optimum air-fuel ratio to keep the engine running at a good efficiency and power. 

  2. On the other hand, the downstream O2 sensor readings are compared with the upstream O2 sensor reading, and when the readings are getting close enough, the vehicle computer will trigger a Diagnostic Trouble Code on Catalytic Converter, as it’s not working well and preventing toxic particles from entering the air.

How many O2 sensors does my vehicle have?

The number of O2 sensors depends on the number of the exhaust pipe. As required, each exhaust pipe has to be equipped with one catalytic converter, and for each catalytic converter, there are two O2 sensors. So there might be two, four, or six O2 sensors in your vehicle.

Oxygen sensor


Can You Drive With A Bad Oxygen Sensor?

Yes, you can drive with a bad oxygen sensor if you can still start your engine and feel little difficulty driving. But don’t leave it alone for over a couple of days, as it might cause safety problems and lead to the malfunction of other parts of your vehicle.

A bad oxygen sensor could cause sluggish and rough driving with stalls, along with poor fuel efficiency and high pollution. And if you leave it there for several months, it may lead to serious problems in the engine and catalytic converter which cost thousands of dollars to fix or replace.

Thus, you need to get the oxygen sensor checked as soon as possible, like go to a mechanic during the weekend. If you have a car diagnostic tool yourself, you can read the OBD2 code and search for possible causes online and try several simple fixes. Sometimes a trouble code indicating that the O2 sensor is malfunctioning could be cleared by cleaning the O2 sensor or replacing a pipe connected.

Oxygen sensors


What Happens When An O2 Sensor Goes Bad?

Since O2 sensors are so critical to your car’s system, it’s recommended to replace your sensors every 60,000 to 90,000 miles. There are a few signs that will help you know when it’s time to take your vehicle in to have the sensor replaced.

Check Engine Light Is On

This is the simplest sign. Those warning indicators on your dash are not just pretty pictures, but they tell you when something is wrong with your vehicle. If you see a check engine light, you better conduct a car diagnostic test and find out what’s wrong with your vehicle.

Bad Gas Mileage

Are you filling up your gasoline tank more often than usual? This is a sign that something isn’t working right and your O2 sensor could potentially be one of the causes. Your gas mileage efficiency will decrease over time, so you’ll need to monitor this to recognize the pattern.

Emission Test Failure

Everyone hates failing, especially in a test, but your emissions test is one that could be costly to pay for (especially when you’d have to pay for a second one). Poor oxygen sensors are one of the most common reasons for failure during an emissions test. Make sure to have your sensors checked by a mechanic prior to your first test to save you time and money.

Rotten Egg Smell

You’ll know it as soon as you smell it. This smell is from burning sulfur and is a symptom of damage in the emission system or a problem with the catalytic converter. The oxygen sensor can fail and lead to a poor fuel/air mixture. If there is not the right balance, it can damage your catalytic converter in your exhaust system, leading to the rotten egg smell.

Rough Idling and Stalling

If you notice that your engine is a little jumpy, bumpy, or stalls and starts, you should definitely have your car checked out, and one of the important things to have your mechanic check while they’re looking at everything are your oxygen sensors.


How Much Does It Cost To Fix An O2 Sensor?

The cost of fixing/replacing an O2 sensor varies depending on the real problem. If you see a Diagnostic Trouble Code related to O2 sensors, such as P0135 or P0141, the problem may lie in the wires, hoses, meta tabs, engine ground corrosion, oxygen sensor, catalytic converter, or the Engine Control Module.

Generally, the cost of fixing an O2 sensor could be:

  • Repair a broken wire $100-$200

  • Repair a leak of exhaust $100-$200

  • Replace the oxygen sensor $200-$300

  • Replace the catalytic converter $400-$2400

repair an oxygen sensor


Repairing Methods for O2 Sensor Related DTC Codes

A faulty O2 sensor may cause a list of related Diagnostic Trouble Codes in your car and turn on the Check Engine Light. One of the most common DTC codes that is related would be P0420. It indicates that the Catalytic Converter is not functioning efficiently, so the vehicle is increasing the output of harmful pollutants. For an idea of how to troubleshoot P0420, check out the video below:

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)


More videos of O2-sensor related DTC codes:

P0171 - System Too Lean (Bank 1)

P0141 - Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)

P0136 - O2 Sensor Circuit Malfunction (Bank 1, Sensor 2)

P0138 - O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)

P0030 - HO2S Heater Control Circuit (Bank 1 Sensor 1)

All videos are produced by nonda Auto DIY Center. Check out their YouTube channel to learn more about DTC codes. 



It is a good idea to not only have the O2 sensors checked with the car isn’t performing well, but also when you do your regular maintenance like oil changes. You can find the problems before they have a chance to potentially damage more parts of your vehicle’s engine. Replacing the O2 sensor is not as complex as you think, but monitoring the vehicle and know when to do it is not as simple. 

That’s why we would love to recommend the ZUS Smart Vehicle Health Monitor Mini, which will:

  • Regularly check your vehicle for problems
  • Explain the Diagnostic Trouble Codes with scan results
  • With additional features such as car finder, mileage tracking, pro dashboard
  • Save the money and time of a trip to a mechanic
  • FREE!

vehicle health monitor

I hope the article above provides you with basic information about the O2 Sensors. Have you changed an O2 sensor? What did you do about it? What do you think is the most important part of the process? Please feel free to comment below and join the conversation!


Top Posts from nonda:

What is a Car Diagnostic Test & How to DIY?

What Does Check Engine Light Mean & How to Fix it?

Best OBD2 Scanner & Code Reader: Complete Buying Guide

OBD2 Codes: What You Need to Know 

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