The functionality of the oxygen (O2) sensor in your car is the same as the nose in your body. It detects, or rather should we say, “sniffs” the oxygen levels in the exhaust gases passing through the exhaust system. This helps the Powertrain Control Module (PCM) fine-tune the air-fuel mixture in the engine for its smooth functionality.
However, just like how a blocked nose can make your day go bad, a faulty O2 sensor can also make your car feel out of breath. While a bad oxygen sensor is not entirely fatal, its ignored and prolonged consequences can be deadly for your car’s life. Here, we will discuss how to detect a faulty O2 sensor in your vehicle, break down the symptoms of a bad oxygen (O2) sensor, explain what causes it to fail, and give you a clear idea of the steps, and costs involved in replacing one.
What is an Oxygen (O2 ) Sensor in a Car?
Fuel in an internal combustion engine needs oxygen to ignite and burn. And just like any good recipe, the proportion matters, therefore a precise amount of oxygen is key in getting the air-fuel mixture right for optimal performance
While more fuel and less oxygen can make the mixture rich, less fuel and more oxygen make the mixture lean. Both conditions can lead to engine damage over time due to inefficient combustion. To regulate this, an O2 sensor is required in the exhaust system.
How Does an Oxygen Sensor Work: Functionality of O2 sensor
- The oxygen sensor is mounted into the exhaust pipe, with the sensor tip inside the pipe, where it can measure the oxygen levels of the exhaust as it passes through. The outside portion of the sensor measures the oxygen of the surrounding air.
- This difference is what creates the voltage signal, a small electrical charge, usually between 0.1V and 0.9V.
- If this voltage level is below 0.45V, it indicates to the car’s computer that the air-fuel mixture has too much oxygen and is burning lean, and if it’s higher than 0.45V, the mixture doesn’t have enough oxygen and is burning rich.
- Based on these voltage outputs, the oxygen sensor triggers the Powertrain Control Module (PCM) to adjust the amount of fuel in the air-fuel mixture entering the engine.
How Many Oxygen Sensors Does a Car Have?
Modern vehicles usually have two O2 sensors. Each catalytic converter is monitored by two oxygen sensors.
The first sensor, known as the upstream sensor, measures the oxygen levels in the exhaust gases before they enter the catalytic converter. Meanwhile, the other sensor is known as the downstream sensor, which measures the same after the exhaust gases flow through the catalytic converter.
Vehicles with dual exhaust systems or multiple catalytic converters (like V6 or V8 engines) may have four or more oxygen sensors.
Common Symptoms Indicating a Bad O2 Sensor
For a vehicular component as tiny as an O2 sensor, detecting a fault in it can be as hard as finding a needle in a haystack. Thankfully, there are a few evident symptoms of a bad oxygen (O2) sensor which indicate that the oxygen sensor in your vehicle has gone bad, which are as follows:
Rough Idling of Engine
If the air-fuel ratio becomes irregular due to a faulty O2 sensor, the ignition timing and combustion intervals might also vary abruptly. As a result, the engine might feel gruff at idle RPM.
Sluggish Acceleration
The irregular ignition timing and combustion intervals due to a faulty O2 sensor can also make the engine struggle to pick up the throttle responses. In such conditions, the vehicle’s acceleration becomes sluggish and inconsistent in regular throttle inputs.
Drop in Fuel Efficiency
Another major impact of a bad oxygen sensor in a vehicle is a noteworthy reduction in fuel efficiency. If the oxygen sensor fails, the amount of fuel in the air-fuel mixture also varies significantly, resulting in the engine burning too lean or too rich fuel, as per the input. In either case, the fuel efficiency drops below the usual figures.
Check Engine Light Glows On
The O2 sensor is one of the various sensors linked to the Powertrain Control Module (PCM), which triggers the check engine warning light in case any of these sensors fail to perform. If the check engine light glows on along with or after a few seconds of sluggish acceleration or rough idling, it can be a clear indication of the failure of the oxygen sensor.
Unusual Sounds from the Engine
A faulty oxygen sensor can also lead to abrupt or inconsistent rattling and knocking noises from the engine. This happens due to carbon buildup in the combustion chamber because of an imbalanced air-fuel mixture. Although these noises might also point to other issues like internal engine damage or clogged injectors, the diagnosis can also detect a fault in the O2 sensor.
Engine Overheating
One of the after-effects of a faulty O2 sensor is the engine running too lean, which is possible if the sensor doesn’t measure the accurate amount of oxygen in the exhaust gases. It can lead to the oxygen sensor sending incorrect signals to the PCM, eventually leading to excessive air in the air-fuel mixture. If an engine continues to burn lean air-fuel mixture, the operating temperature of the engine also increases, which can result in overheating.
Poor Results in Emissions Test
If your vehicle struggles during a routine emissions test and shows higher-than-normal exhaust pollutants, a bad oxygen sensor could be the culprit. This is because, in case of a faulty oxygen (O2) sensor, the engine burns an incorrect proportion of the air-fuel mixture. This can increase the amount of pollutants in the exhaust gases, such as CO, NOx, and HCs. More pollutants in the exhaust gases increase the possibility of the vehicle failing the emissions test.
Why Does an O2 Sensor Fails?
Given that it is subjected to excessive work and exposure to harmful elements, the functionality and efficiency of an O2 sensor deteriorate due to various factors. Following are some of the usual culprits behind the failure of oxygen sensors:
Usual Wear-out due to Age
All mechanical and electrical components, including sensors, have a finite lifespan. People often question, how long do oxygen (O2) sensors in cars last? While in older vehicles, the oxygen sensors last 3-5 years or 30,000-50,000 miles, the newer vehicles have more efficient O2 sensors lasting even more than 100,000 miles or up to 10 years.
Carbon Build-up
As the oxygen sensors are present within the exhaust system, they can get covered up by carbon, a by-product of inconsistent burning of air-fuel mixture. The deposition of carbon over the oxygen sensor’s accuracy leads to its failure.
Contaminants
Apart from carbon deposition, a few other by-products of irregular combustion, including engine oil or coolant leaks, can also enter the exhaust system, act as contaminants, and damage the O2 sensors.
Faulty Wiring
A fault in the O2 sensor can also be due to the collective failure of the powertrain control module or wiring linked to it and the oxygen sensor.
Use of Excessive Fuel Additives
While fuel additives are usually helpful in cleaner and more effective combustion within the engine, their overuse can lead to the failure of the oxygen sensor or any other component.
Can I Continue to Drive with a Faulty Oxygen Sensor?
Technically, yes, you can keep driving if your oxygen sensor isn’t working right. But should you? Definitely not. When that sensor goes bad, your engine starts making poor decisions. You might burn more fuel than you need to, your emissions go up, and overall performance takes a hit. Keep ignoring it, and you risk doing real damage to your engine, which could cost you a lot more than just a sensor replacement. Therefore, the smart move is to get it checked and swapped out before a small issue turns into a major repair bill.
What’s the Cost of an Oxygen Sensor?
Like any other vehicular component, the prices of an O2 sensor also vary depending on the make and model of the vehicle. Other factors like the type of sensor and labor costs of its installation also affect the overall costs.
- The prices of an O2 sensor usually start at around $20-50 for a basic aftermarket unit, which can go up to $100-150 for genuine OEM parts or even to $300 for a high-end sensor.
- The installation cost for an oxygen sensor begins at around $100-150 for an economical, mass-oriented vehicle. However, it can go up to $200-300 for luxury vehicles and even up to $500-600 for high-performance sports cars.
Conclusion: Repair or Replace?
While automotive sensors are highly effective in their operation, their repairing procedures are so tricky that it is always advisable to replace them altogether. The same goes for an O2 sensor. If it malfunctions, it is better to replace it as the replacement process and repair costs are much easier, quicker, and more affordable. An unprofessional attempt to repair the oxygen sensor can result in more troubles in the bigger picture.
As we mentioned, a faulty oxygen sensor isn’t too catastrophic. However, ignoring its symptoms for a prolonged duration can lead to more serious concerns like significantly reduced fuel efficiency and performance, along with increased wear and tear of the engine and exhaust system. In case you experience any of the symptoms of a faulty O2 sensor, a thorough diagnosis and prompt replacement of the sensor would solve the purpose.
FAQs
Q1.What happens when the oxygen sensor is bad in a car?
If the oxygen sensor malfunctions, the vehicle faces issues like reduced fuel efficiency acceleration, rough engine idling, engine overheating, check engine light glowing on, poor emission test results, and unusual sounds from the engine.
Q2.Can you drive a car with a bad oxygen sensor?
Driving a car with a faulty O2 sensor for a prolonged time can lead to a significant drop in acceleration and fuel efficiency and even more significant mechanical or electrical losses in the future. So, to avoid running on an irregular air-fuel mixture, replace the faulty oxygen sensor as quickly as possible.
Q3. How much does an O2 sensor cost?
An oxygen sensor costs between $50-300, depending on the make and model of the vehicle. Also, the installation cost of an O2 sensor varies between $150-600, depending on the type of vehicle.
Q4.How long do car oxygen sensors last?
Oxygen sensors last 3-5 years or 30,000-50,000 miles in older vehicles, whereas they can last even more than 100,000 miles or up to 10 years in newer vehicles.
Q5.How many O2 sensors are in a car?
Modern cars usually have two O2 sensors within the catalytic converter – one for measuring the oxygen levels in the exhaust gases before they enter the catalytic converter and the other for measuring the same after the exhaust gases flow through the catalytic converter.