Skip to Content

What Are The Symptoms Of A Bad O2 Sensor? [ 2022 Updated ]

What Are The Symptoms Of A Bad O2 Sensor? [ 2022 Updated ]

The sole function of the oxygen sensor in your car is to gauge the remaining oxygen level in the exhaust fumes that leave your vehicle’s engine.

Sometimes, the oxygen sensor starts malfunctioning, and you need to get it replaced. Remember, this particular component of your car doesn’t cost much.

So, replacing it wouldn’t hurt your wallet. However, other car parts might sustain damage if you overlook this issue. If this happens, you would repent shelling out higher amounts to get them fixed.

In case you have a faulty oxygen sensor, the car would have a wrong ratio between the fuel and air during combustion. This would ultimately lead to inefficiency in combustion, and the engine output would be weak.

As a car owner, you should know the signs of a malfunctioning oxygen sensor. This article has extensively discussed the symptoms of a faulty oxygen sensor.

What are the symptoms of a bad o2 sensor?

1. Failed emission tests

The function of the oxygen sensor is to reduce the contaminants of the car’s air emits from the tailpipe. It monitors the air-fuel mixture in the car.

So, to pass the emission tests, your car needs to have a properly functional oxygen sensor. This is also necessary to complete the registration of your vehicle. So, if you find that your vehicle has repeatedly been failing the emission tests, you must inspect the oxygen sensors.

2. Rough idling, misfiring and stalling

The oxygen sensor ensures effective combustion in your car by controlling the combustion intervals and engine timing. This way, it wouldn’t allow the fuel-oxygen proportion to go out of balance.

In case you detect frequent rough idling, misfiring, or stalling of your car, there can be an issue with the oxygen sensor. Some other symptoms include the engine’s hesitation, power loss, and stalling of the car when you try to start it. Besides, your vehicle would be sluggish when you navigate it.

Rough idling is one of the foremost indicators of a malfunctioning oxygen sensor. Next, you would experience misfiring, and eventually your car would start stalling.

3. Error codes

With a defective oxygen sensor in your car, you will likely find a flashing check engine light. When you have a faulty O2 sensor, the CEL wouldn’t trigger on its own. However, this would cause some other system parts to fail, leading to the illuminated light.

You will find some error codes when you use an OBDII diagnostic scanner. Some of these codes include P0131, P0136, and P0172. So, you need to get to your car mechanic, who would diagnose the issue and trace the problem back.

4. Poor fuel economy

If the oxygen sensor in your car starts malfunctioning, you would notice a dip in the vehicle’s fuel efficiency. In these cases, you need to make necessary adjustments in the carburetor settings of the car or get a new vacuum hose to replace the loose one.

The poor fuel economy results from malfunctioning oxygen sensors for computer-controlled and fuel-injected cars. You need to replace the parts, which wouldn’t cost you too much.

5. Poor performance of the engine

You would get to know that the oxygen sensors are not functioning if the engine performance is weak. Prior to this, you would already experience stalling, misfiring of the engine, and rough idling.

When your car starts to move, sometimes these symptoms might disappear.

In case you overlook the issue, the situation might aggravate, leading to power surges, hesitation of the engine, speed stasis, sputtering, or loss of power. So, consulting a reputed mechanic would be the most viable move.

6. Noises in the engine

A bad oxygen sensor would not be working as a reliable emission device. The car’s combustion chamber would get more carbon deposits due to a poor mixture of air and fuel. This would also cause pinging or knocking noises in the engine.

However, this issue might stem due to other factors as well. However, if you have noises in the engine, make sure to inspect the oxygen sensors.

7. Black fumes

When you have malfunctioning oxygen sensors, there would be an imbalance in the volume of fuel and air. This would adversely affect combustion efficiency, causing backfiring, unburned fuel, or the emission of extremely dark smoke that resembles soot from the car’s exhaust. Moreover, you would experience hard-starting problems, poor idling, and high fuel consumption.

8. Failure of the catalytic converter

You must know that your car’s emission system includes catalytic converters. They alternate between the lean and rich mixtures to balance the amount of air in your car’s exhaust.

In the process, it reduces the harmful gasses the vehicle releases into the atmosphere. Even though it constitutes a key component of your car’s emission system, it significantly depends on the oxygen sensors for proper functioning.

As a result, the catalytic converter would sustain damage and completely fail in case the oxygen sensors start malfunctioning and the PCM gets wrong readings.

9. Odor from the exhaust

You would get the odor of rotten eggs or heavy gasoline from the tailpipe. Besides, there would be a residue of black smoke. Both these issues point to problems with faulty oxygen sensors. However, these issues can also stem from problems in your car’s injector or fuel system.

In any case, the symptom means that the engine has excess fuel, and you need to fix the air-fuel mixture in the car. So, you need to troubleshoot your vehicle, considering the problems in the oxygen sensor and the fuel system.

How can you tell if an oxygen sensor is bad?

If you have a bad oxygen sensor, you would get to know the issue by observing the symptoms we have discussed. These include the flashing of the engine light, poor fuel economy, rough idling, engine misfires, stalling of the car, and poor engine performance.

Moreover, your car would emit thick black smoke like soot and consistently fail emission tests. Also, you would experience an extremely foul smell like rotten eggs. The catalytic converter in your car would also fail under such circumstances.

Can you drive your car with a bad O2 sensor?

In most cases, a faulty oxygen sensor doesn’t pose any immediate threat to your car. So, this isn’t an emergency that you need to address instantly.

There have been rare instances where a malfunctioning oxygen sensor has caused the vehicle to shut down. Oxygen sensors are responsible for dispatching information to your car’s computer so that it can carry out necessary adjustments in the fuel-air ratio.

You would also find the check engine lights blinking when the oxygen sensors fail completely.

However, a driver can continue to drive until the faulty sensor causes graver issues. However, it would be wise not to let the condition of your car aggravate to this, as you won’t like shelling out expensive repair costs.

Can a bad O2 sensor cause hesitation?

Yes, a faulty oxygen sensor can cause stalling and hesitation in your car when you try to start the engine. You would also encounter misfires in the engine if you have a bad oxygen sensor.

How do you know if your oxygen sensor is working?

You need to observe possible symptoms of a faulty oxygen sensor and determine whether this component works perfectly in your car. In case the oxygen sensor is bad, you would experience rough idling.

Besides, a defective oxygen sensor would have an adverse impact on the combustion interval, the timing of the car’s engine, and other crucial functions.

Also, you would experience slow acceleration and stalling. In case you don’t experience any of these issues with your car, it indicates that your oxygen sensor is in proper operational conditions.

What are the reasons of Premature O2 Sensor Failure?

Premature failure of the oxygen sensor in your car takes place due to the following reasons.

  • The buildup of excessive carbon in the engine and debris like dirt and grime can lead to these issues. These elements enter the fuel systems and air intake, inflicting damage to the oxygen sensors.
  • The exhaust manifold, exhaust system, or catalytic converter might sustain physical damage.
  • Your oxygen sensor might prematurely fail if you use low-grade fuel, or when the fuel contains contaminants. Besides, it might happen in case the engine burns excess oil or the oxygen sensors get clogged.
  • In case you have skipped one of the periodic maintenance of your car, or haven’t changed the fuel or air filters and spark plugs, the oxygen sensor might fail prematurely.
  • If you continually use fuel additives, it would adversely impact the exhaust fumes or the car’s air-fuel mixture.
  • In case you fail to get your car inspected at least once annually, you can have issues with the oxygen sensor.
  • Failing to comply with the recommended schedule for replacing the oxygen sensor can also lead to the malfunctioning of this component.
  • Poor maintenance of your car might cause the oxygen sensors to get clogged.


Depending on different factors, your car’s oxygen sensors can last between 30K to 100K miles. So, you need to get these components inspected regularly and replace them.

These sensors are available at prices as low as $30. So, a simple replacement on time can save you other hassles when the malfunctioning component starts messing up other functions of your car.

Now that you know the signs of a bad oxygen sensor, you can be prompt with your action. It would be wise to replace the sensor as soon as you detect it delivering substandard performance.