8 Symptoms Of A Bad Oxygen Sensor (& Replacement Cost)

If you’re like most car owners, you probably don’t think much about your car’s oxygen sensors until it’s causing a problem. But did you know that a bad oxygen sensor can impact your car’s performance and even lead to decreased fuel efficiency?

In this guide, we cover the symptoms of a bad oxygen sensor, so you know what’s going on. The oxygen sensor's function is also discussed. We will show you how to locate it. It is also discussed how to repair it, what the cost might be and why this should not happen.

Índice de Contenido
  1. 8 Bad Oxygen Sensor Symptoms
    1. Check Engine Light Illuminates
    2. Reduced fuel economy
    3. Rough Idle
    4. Stalling Engine
    5. Poor Motor Performance
    6. Failure to pass the emissions test
    7. Strange Sounds
    8. Failure of the catalytic converter
  2. Oxygen Sensor Location
  3. Oxygen Sensor Function
  4. Oxygen Sensor Replacement Cost
  5. Commonly Asked Questions
    1. What happens if you don’t replace the oxygen sensor?
    2. Do I have to drive with an oxygen sensor that is defective?
    3. Do I have to buy a new oxygen sensor?
    4. Is the engine light going to reset when you replace the O2 sensor

8 Bad Oxygen Sensor Symptoms

A bad oxygen sensor can lead to engine problems, as well as a check engine lamp on the dashboard.

A bad oxygen sensor can lead to the following symptoms:

Below is a list of all eight possible signs of an oxygen sensor failure.

Check Engine Light Illuminates

The Check Engine Light is the first indication that there's something wrong. In many cases, there can be a trouble code related to the oxygen sensor, and you don’t notice any other symptoms at all. 

The oxygen sensor is responsible for all trouble codes, including P0030 and P0131. Your code scanner might show P0137 and P0140 as well as P0141, p0161, p0172, and a few other codes. You can also see trouble codes related to air-fuel mixture issues that may ultimately be caused or triggered by your oxygen sensor.

Reduced fuel economy

In order to ensure proper combustion chambers, the mixture of fuel and air must be equal. If there’s more fuel than air, your defective oxygen sensor might not be able to detect it. 

Your gas mileage will decrease as you burn more fuel in your engine. You will end up with more gas mileage and less money at the pump. 

Rough Idle

If you’ve noticed that the car runs roughly when it’s stopped or parked, the idle is off. Normal idle speed for a car is around 1000 RPMs. The oxygen sensor could have a problem if the car starts to rev up.

However, a rough idle isn’t always indicative of a bad oxygen sensor. It could mean any component that’s responsible for the air-fuel ratio is defective. That’s why you need to compare this symptom with the others. 

READ MORE: What Causes Car Engine Rough Idle? How To Fix It

Stalling Engine

If the motor idles too much, it can stall. This problem normally starts out as a misfire and doesn’t normally occur until the problem has been left unresolved. 

The engine will eventually shut down if it can't sustain enough power to continue to work. It should be possible to start it again but you cannot guarantee that.

Poor Motor Performance

The engine's performance can be affected if it is not able to continue the combustion process. It’s going to be weaker than normal, especially when you try to push on the gas pedal. At first, this problem can be so subtle that you don’t notice it’s occurring. 

These problems can get worse, making driving more difficult. That’s why it’s important to have the fault looked at as soon as you notice it, especially before the lack of acceleration leads to an accident on the road. 

Related: Why is my car losing its power while accelerating? (Here’re the Causes)

Failure to pass the emissions test

These oxygen sensors form part of your vehicle's emission control system. If they aren’t working, there could be an imbalance in the exhaust, which would be read through an emissions test. 

Although there may be many reasons for failing these compulsory tests, oxygen sensors are the main culprit. Check the computer for codes once the test fails. 

Strange Sounds

If the oxygen sensor does not monitor the fuel mixture properly, there could be an excess carbon buildup inside the combustion chamber. The motor could experience a poor running mixture.

Pre-ignition can be caused by a lean mixture. This causes pinging and knocking sounds. These noises may also be caused by a blocked fuel injector or bad fuel. These sounds are most commonly heard when the engine is under load. 

RELATED: 7 Engine Noises You Should Not Ignore (& What They Mean)

Failure of the catalytic converter

How will the system react if it has a poor oxygen sensor? Because of an imbalance in fuel and air, eventually the catalytic conversion will fail. For the catalytic converter to be protected from harm, it is essential that oxygen sensors are in optimum working order. 

It’s never cheap to replace a catalytic converter. You should replace the catalytic converter because of its potential for causing bigger problems. 

Oxygen Sensor Location

It is located in the exhaust system. You can find it near the engine, or in the exhaust manifold. There are many oxygen sensors in cars, and they all monitor the amount of exhaust gas.

If there is more than one oxygen sensor in the vehicle, it will place the other behind the catalytic convert. This sensor compares previous and subsequent readings to monitor the performance of your converter. 

RELATED: How to Bypass Oxygen Sensors – Can & Should You Do it?

Oxygen Sensor Function

After the air and fuel have ignited, the car's engine produces exhaust gas. There are many components in these exhaust gases, such as carbon and oxygen. The oxygen sensors monitor the level of these gases in the exhaust as it’s leaving the motor. The sensor can measure the amount of oxygen that is being emitted from the combustion process.

The engine control module (ECM) receives the information from the oxygen sensor. This computer processes all information to adjust the fuel/air ratio. If the ECM reads that there’s too much oxygen, it will adjust other sensors to add more fuel and vice versa. You will be left with either an engine problem or a rich running condition. 

The bad oxygen sensor can cause problems in your engine and other parts. The catalytic converter's expensive component will be further worn if the exhaust is not properly balanced. That’s why repair should be performed as soon as possible. 

Oxygen Sensor Replacement Cost

A bad oxygen sensor can cost you anywhere from $50-5050. This price depends on many factors. Cost depends on the type and make of your car.

The cost of a smaller, more economical car is likely to be lower than that of a bigger SUV or truck. The overall cost of luxury cars can be higher due to the more costly parts. A specialist mechanic might be needed to repair your luxury car, as opposed to a small Chevy.

Other important factors include the labor rates. If you can replace the oxygen sensor yourself, there’s no reason to pay a professional mechanic. You can save lots of money by replacing the oxygen sensor yourself. It might cost $20 to $175. These fixes can be done with the help of a service manual, or repair manual.

You can end up with serious problems if you delay in changing the oxygen sensors. Procrastinating on this repair can lead to other damages. What could have been an easy repair may quickly escalate into something much more complicated. That’s why we always recommend changing the defective oxygen sensor at the first sign of trouble. 

Comparing the cost of changing out your catalytic converter with replacing the oxygen sensor will show you how much it costs. A typical replacement catalytic converter will cost you between $1,000 and $2,500. This is if it's being done by professionals. However, most of this cost isn’t related to the labor costs but how expensive the part is. That’s why it’s best to spend the money upfront and get the oxygen sensors working right than deal with what’s coming down the road as a result of neglect. 

Commonly Asked Questions

What happens if you don’t replace the oxygen sensor?

If the oxygen sensor isn’t replaced, the car’s computer won’t be able to monitor the air/fuel mixture accurately. As a result, the car’s engine will run either too rich (with too much fuel) or too lean (with not enough fuel). These can lead to poor fuel economy and excessive emissions. It can cause engine wear, leading to expensive damage such as the internal engine parts or the catalytic converter.

Do I have to drive with an oxygen sensor that is defective?

Although you may be able to drive your car without a bad oxygen sensor, this isn't recommended. It can make the engine run more lean and richer than normal. You can drive your car if the oxygen sensor is bad, but only if you're aware of all the possible risks.

Do I have to buy a new oxygen sensor?

In most cases, it is quite easy to replace the oxygen sensor. This will depend on what make and year your car is. If the car has rust or is very old, it may become stuck to the oxygen sensor. It can sometimes be impossible to get it out without special tools.

Is the engine light going to reset when you replace the O2 sensor

This depends on your vehicle's make and model. For most cars, the answer is yes – the check engine light will reset after replacing the O2 sensor, but it can take a while. The car monitors the emission levels every time it starts the engine. The engine control module may need to run the check several times before it detects that oxygen sensors are working properly and turns off the light. So it’s definitely easier to clear the error code with a scanner.

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