What are the Symptoms of a Bad (O2) Oxygen Sensors?

The oxygen sensor is responsible for measuring the remaining oxygen levels from the residual exhaust gases that exit your vehicle’s engine. The sensor then transmits the measurements it gets to the Powertrain Control Module of the car that triggers accurate fuel injection levels to ensure efficient fuel combustion in the engine.

Therefore, having a bad oxygen sensor means that your vehicle will experience air-to-fuel ratio problems that can manifest in several ways, including fuel combustion inefficiencies and weak engine performance troubles.

Also, since oxygen, the messages oxygen sensors send to the car’s PCM, help it regulate the fuel mixture and the exhaust gas released to the environment, a car with a failing oxygen sensor releases worse carbon-based compounds that increase global warming in the environment.

how to test a bad o2 sensor

What are the Symptoms of a Bad Oxygen Sensor

Oxygen sensors are necessary car parts because they check the ratio of air to fuel in your car’s engine and relay messages to the computer so it can adjust it accordingly.

The oxygen content in the engine depends on the environmental conditions. Elements like temperature, altitude, air pressure, engine temperature, and engine load are the factors that affect the ratio of gasoline and oxygen during combustion. When your engine burns with a lean mixture with a high oxygen-to-fuel ratio, the exhaust generates and releases more pollutants into the environment.

Apart from the fault code of O2 sensors (P0131) sent to signal malfunctioning sensors, here is how you can tell if an oxygen sensor is bad.

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Check Engine Light Comes On

The first symptom of a bad o2 sensor is an illuminating Check Engine Light. The Check Engine Light illuminates whenever any engine part malfunctions. You should always contact an auto mechanic whenever you have an illuminating Check Engine Light for inspection because the light turns on for many different reasons. The only way to correctly diagnose the cause is if a professional inspects your car.

Bad Fuel Economy

When you have an abnormal fuel consumption increase, the chances are that your vehicle has a bad oxygen sensor. Whenever the fuel is either too rich or too lean, the engine fuel combustion loses efficiency. Because oxygen sensors deteriorate gradually, you will also notice the consumption increasing slowly.

You can also note a foul egg-like smell as the fuel burns because of Sulphur and Nitrogen residue production. Another symptom of failing oxygen sensors is black smoke production at the exhaust because of the low fuel economy. Always keep tabs on the amount of fuel you fill at the station and its consumption rate to notice whenever your oxygen sensor has problems.

Misfires and a rough engine idle

When your oxygen sensor starts failing, you will notice your vehicle frequently misfiring, running roughly and irregularly when idling. Failing sensors come with other engine performance problems like power loss, engine hesitation, and stalling when you start the car.

As mentioned before, the oxygen sensor messages help to control the engine timing and combustion intervals. These affect the air to fuel ratio, which is essential for effective combustion.

Therefore, a faulty sensor disrupts these engine functions and causes rough and irregular engine running when idle or other engine-related problems.

Weak Engine Performance

Whenever there are combustion difficulties in the engine processes, the vehicle will experience a weakened engine performance. When you have a bad oxygen sensor, the air-to-fuel ratio will balance inaccurately, causing insufficient combustion.

“Can a bad O2 sensor cause poor acceleration?” Yes, a lousy sensor sends wrong messages to the car’s Powertrain Control Module that controls the fuel ratio your vehicle uses. Improper balance causes incomplete combustion, which interferes with power transmission to the mechanical parts that drive the car. Therefore, you can step on the pedals and get nonexistent or limited acceleration.

Failing Emission Tests

Another sign that you may be dealing with a bad oxygen sensor is continually failing emission tests. Some counties and states require vehicles to go through regular emission tests to control environmental pollution. The oxygen sensor is in the exhaust manifold and assists with emission control.

Therefore, failing the emission tests may indicate your oxygen sensor and control system has a problem.
Since it is not only the oxygen sensor and fuel ratio regulation system that causes faulty emissions, you should consult a professional to diagnose your car’s problem accurately.

Rough Engine Sound

When you drive your car for a while, you get used to it and can easily detect worrying engine noises. A well-functioning engine is relatively silent. Therefore, when your car makes loud noises, mostly when idle, the chances are that you have a bad oxygen sensor problem.

A faulty oxygen sensor affects fuel injection timing and combustion levels, thus producing unpleasant noises. Poor fuel combustion makes your car hard to accelerate and can cause it to shut off suddenly when you are on the road.

Black Smoke Emission

Black smoke emission at the exhaust signalizes inefficient combustion within the engine. The oxygen sensor’s primary role is to send information to the engine control unit and tell it how to balance the air and fuel quantities for your car efficiently and, thus, prevent any emissions.

Bad oxygen sensors cannot accurately control the air-to-fuel ratio, which means that your combustion process will occur poorly, leading to performance problems and black smoke residue. Your car will also have high fuel consumption with poor idle and hard starting problems.

Smoke Emission and Global Warming

Car smoke emissions account for a fifth of all smoke emissions that deplete the ozone layer and cause a global warming effect on the environment. Vehicles with incomplete combustion of carbon produce heavy smoke that accentuates this negative environmental effect. Therefore, having functional oxygen sensors not only makes your car drive efficiently but reduces the environmental impact of global warming.

bad oxygen sensor symptoms

What happens to a car when the oxygen sensor is bad?

When you have a bad oxygen sensor, either it will send incorrect feedback to the car’s PCM or it will not send any messages at all. That makes it difficult for the vehicle to maintain accurate oxygen-to-fuel ratios that make your car run efficiently. Therefore, as explained earlier, when you have a failing oxygen sensor, you will have inefficient fuel consumption, you may experience misfiring, and you will produce sooty exhaust fumes.

Can a bad O2 sensor cause a loss of power?

A faulty O2 sensor relays false readings to the computer causing inaccurate adjustments to your combustion engine’s intake and fuel system. These conditions cause inaccurate shifting points directed by your car’s transmission control module. Incorrect timing and fuel injection affect the fuel combustion responsible for efficiently running your vehicle. Inadequate combustion eventually translates to a lack of sufficient power for acceleration and other engine functions.

Will a bad O2 sensor cause sputtering?

Oxygen sensors’ primary function is to measure how rich or lean the exhaust gases are at the car’s combustion chamber. The vehicle then adjusts the amount of fuel entering the engine depending on the oxygen sensors’ readings. A malfunctioning sensor either puts more or less fuel into the engine than the car requires, causing it to sputter.
That is why you should replace oxygen sensors regularly to ensure the correct air-to-fuel ratio balance.

Can an O2 sensor cause a car to cut off?

It is highly unlikely that a faulty oxygen sensor will cause your car to shut off. The O2 Sensors only relay information to the PCM to adequately control the fuel and air mixture. When an oxygen sensor completely fails, the car will illuminate the check engine light but continue with ordinary function until worse problems cause the car to stop.

Can you drive your car with a bad oxygen sensor?

Oxygen sensors are located either before or after the catalytic converter. Therefore, when your oxygen sensors malfunction and the check engine light comes on, you will get a P0136 generic code that indicates trouble with oxygen sensors on the exhaust system’s first bank. The code typically means that your oxygen sensors are dirty or going bad.

Although your vehicle will continue to run with faulty oxygen sensors and an illuminating check engine light, you should not drive it more than required. You will notice that the car will run sluggishly and have occasional misfires. The poor fuel-to-oxygen ratios because of the bad sensor can cause further mechanical problems if you don’t fix your car as soon as possible.

How much does it cost to replace an oxygen sensor?

The cost of replacing your vehicle’s oxygen sensor depends on your car model and your mechanic’s labor cost. A new oxygen sensor can cost you about $50 to $100. The mechanic’s labor cost can be as high as $200.

Most mechanics’ labor rates range from $50-$150 per hour. Therefore, you should be prepared to pay around $100 as labor costs because oxygen sensor replacement is a simple process that takes approximately 30 minutes for professionals with the right toolbox for mechanics.

You can attempt to replace the oxygen sensor yourself if you have the required equipment, but beware that some vehicles may need you to remove several other parts for you to access the O2 sensors.

Bad Oxygen Sensor Symptoms YouTube

Final Words

When the oxygen sensor of your vehicle measures the oxygen levels of your exhaust gases, it sends this information to the Powertrain Control Module (PCM), which determines the correct air-to-fuel ratio for your engine in real-time. The sensor is located in the exhaust system and allows the fuel injection and engine timing to work efficiently, assisting with emissions control. The oxygen sensors transmit data to the vehicle’s PCM to maintain the optimal air-to-fuel ratio for your engine.

A bad or failing oxygen sensor will affect exhaust emissions and engine performance, so there are things to watch for before your oxygen sensor completely fails. When you experience misfires, have bad engine mileage, or have black emissions from your exhaust, you should check and replace your oxygen sensor before your car experiences more damage.


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

2 thoughts on “What are the Symptoms of a Bad (O2) Oxygen Sensors?

  1. Hi, kindly accept regards to the good information about cars. I look forward to more updates.


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