Bad Oxygen Sensor Symptoms, Location & Replacement Costs

Bad Oxygen Sensor Symptoms

The oxygen/o2 sensor is an important part of any efficient vehicle. It helps keep the oxygen levels at the exhaust system checked and also contributes to a cleaner and more efficient engine. Because of the essential role of this component in emission control, you must learn all about bad oxygen sensor symptoms.

Getting your car’s emission tests done regularly is one way to determine if there are problems with your oxygen sensor as well as other components of your engine.


What is An Oxygen Sensor and Its Location?

Oxygen Sensor Location

Your vehicle’s oxygen sensor determines the oxygen levels of the exhaust gases that leave the engine. The information that the O2 sensor gathers is needed by the car’s Powertrain Control Module or PCM to find out the accurate air to fuel in your engine.

The oxygen sensor is situated in the exhaust system. This keeps the fuel injection and the engine timing to work seamlessly.

Bad or Failing Sensor Symptoms

If there is something wrong with the oxygen sensor, the internal combustion system will be affected, creating all kinds of engine problems. But luckily, these symptoms are very easy to recognize. Here are some of the most common bad o2 sensor symptoms.

1. Blinking Check Engine Light

One of the most common O2 sensor symptoms is a flashing check engine light. The o2 sensor can influence air and fuel combustion. And if the oxygen sensor finds there is less oxygen from the exhaust gases post-combustion, the engine control system will keep on correcting this.

If the oxygen sensor is broken, the engine control system will overlook this problem, and this can result in poor engine performance. The module will also know that there is a problem with the engine, and this can trigger the check engine light on your car's dashboard. In modern cars with built-in computers, you may find the error code P0172. This code means there is a problem with the oxygen sensor.

2. Rough Idling Engine

Rough idling is when the engine is not steady when the vehicle is parked or when it’s stopped. Normal RPM for an idle engine is 1,000, but if you get 2,000 or 3,000, then you have a rough idling engine. This is another common o2 sensor failure symptom.

Idling may also be a symptom of other car problems. And aside from idling, engine timing will be harder for the control module to fix. When this happens, you will eventually get combustion intervals with misfires.

Read Next: what are symptoms of failing idle air control (IAC) valve

3. Poor Fuel Economy

If there are air and fuel in the combustion cylinder, there is a higher fuel amount compared to air. This may not be detected by a broken O2 sensor. There will be more fuel burned in the engine than what you need leading to poor fuel economy. You'll be spending more on gas day after day with a bad O2 sensor.

4. Poor Engine Performance

Another oxygen sensor symptom of failure is poor engine performance. When there's a problem with the regular combustion process of your engine, you will eventually get a weaker engine. You will feel this when you're on the road. As you press on the gas, acceleration will become very limited.

5. Emission Test Failure

The o2 sensor is situated on the manifold of your car’s exhaust system, and thus, it also helps with emission control. If regular emission testing is required in your state or country, your car with a broken oxygen sensor may fail the test.

And you don’t need to wait too long for an emission test. If you suspect that there is something wrong with your car’s oxygen sensor function, take it to a certified car emission testing center in your city or state.  The results will determine if you need to have your vehicle checked or your oxygen sensor replaced.

6. That Rotten Egg Smell

If you have a bad o2 sensor, air and fuel ratio readings may not be accurate. There may be too much fuel in the engine, and your car's gas mileage may also be reduced. Excess fuel in your engine can have a sulfuric or rotten egg smell; sometimes, there is black smoke coming from the exhaust. So if you're filling the gas tank often, take note of how much and how often you fill-up.  If you're constantly out of gas, then have your car checked by a certified mechanic right away.

Another interested post: how do i fix white smoke from exhaust

When To Replace The Oxygen Sensor & Replacement Cost

Oxygen Sensor Replacement Cost

Like most car components, the oxygen sensor may also suffer from wear and tear. Replacing the sensor is necessary to ensure that your vehicle is safe, fuel-efficient, and will perform its best on the road.

If your car was manufactured in the past 15 years, then the sensor must be replaced for every 60,000 to 90,000 miles. As an oxygen sensor wears out, it will be less likely to provide accurate readings. Keeping with your oxygen sensor replacement schedule will help prevent failure and will lower the level of emissions that your car sends into the atmosphere.

The cost of oxygen sensor replacement is from $250 to $400, and this depends on the make and the model of your car. An oxygen sensor cost from $130 to $250. Labor costs may depend on the garage or mechanic, and it is from $120 to $150.

As soon as you see a check engine light and you notice poor gas mileage, we recommend booking a service with a professional car mechanic. You may also ask for a mechanic to come over and fix a broken oxygen sensor at your home or office, but this may cost extra.

Final Words

As soon as you notice any of these bad oxygen sensor symptoms, have your car checked right away. You may still be able to drive with a broken oxygen sensor, but eventually, your engine will be less efficient, and you’ll be spending more on fuel. It’s best to have your car checked yearly for all engine troubles. This is good for you and good for the environment too.


About the Author JamesL Davis

James is a certified auto technician specializing in commercial vehicles. With 30 years of experience under his belt, James has encountered almost every type of automotive issue there is! Besides his day job at the repair shop, he is also an amateur race car driver.

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