Of all the sensors on your car, one of the most vital is the oxygen sensor, also known as the O2 sensor. The oxygen sensor tests your car’s exhaust as it leaves the engine and tells your vehicle’s computer how much oxygen is present in the exhaust.
Despite the crucial nature of this sensor, many people don’t know why they need it, or why it needs to be replaced when it fails, or even how to tell when it fails. Because this sensor plays such a crucial role in your engine’s performance, it is important to know when to replace your old oxygen sensor with a new one.
How does an oxygen sensor work?
As far as cars go, oxygen sensors are relatively new. They were first introduced in 1976, on a Volvo. By 1980, they became commonplace on vehicles in California, the first state to require lower emissions for environmental reasons. These emissions laws were spread nationwide by 1981, and all cars and trucks were required to have at least one O2 sensor.
The O2 sensor is located inside the exhaust manifold and produces its own voltage when it gets hot. The oxygen sensor needs to be about 600 degrees to work correctly. It contains a zirconium ceramic bulb coated in porous platinum. The outside of the bulb is exposed to gases in the exhaust, while the inside of the bulb is vented internally through the body of the sensor to the outside atmosphere. The sensor will test the gases in the exhaust against the outside atmosphere, and produce voltage based on the difference. The greater the difference, the more voltage the sensor will produce.
The sensor will usually produce a voltage of about 0.9 when there is a lot of oxygen in the exhaust, meaning that not enough oxygen is being burned. This is referred to as the fuel mixture burning “rich”. When the fuel mixture is burning “lean”, meaning it is burning too much oxygen, the voltage can drop to 0.1. The ideal voltage reading from the oxygen sensor is approximately 0.45, meaning the fuel mixture is at equilibrium.
When the vehicle’s computer receives a voltage reading from the O2 sensor, it will adjust the fuel mixture accordingly by adding or restricting oxygen or adjusting the fuel timing. This flip-flopping back and forth is happening semi-constantly within your engine at all times, depending on speed, engine load, and engine temperature.
Where is the oxygen sensor located?
Newer vehicles will actually have two oxygen sensors working in conjunction. One of these O2 sensors, called the “upstream” sensor, will be located on the exhaust pipe near the engine, while the other, the “downstream” sensor, will be nearer to the catalytic converter. These readings will be measured against each other for supreme accuracy.
If your vehicle has dual exhaust pipes and is newer, you will have two O2 sensors for each exhaust pipe, for a grand total of four O2 sensors.
When should I replace my oxygen sensor?
Oxygen sensors are not like air filters or oil filters; they do not need to be replaced regularly. They only need to be replaced when they stop working.
Unfortunately, there is no way to really pin down a time when an oxygen sensor should be replaced. There isn’t a warning light on your car that will tell you when your O2 sensor is beginning to fail. Your O2 sensor’s lifespan will vary depending on the age and wear the vehicle experiences. Older vehicles typically need new O2 sensors in as little as 60,000 miles, while vehicles manufactured after 1996 could easily go 100,000 or more before needing a new oxygen sensor.
No matter the model of your vehicle, however, there are telltale signs that your O2 sensor is going bad.
Signs you need a new oxygen sensor
Your check engine light could potentially alert you that your O2 sensor is bad. However, an illuminated check engine light could mean anything from an engine misfire to a loose gas cap, so it is always necessary to investigate further when your check engine light is on. Repair shops will be able to test what triggered your check engine light and alert you if it is your O2 sensor.
There are also several indications in the general performance of your vehicle that your O2 sensor is going bad. Your car could have a rough idle (meaning there is a vibrating or shaking feeling during idle), misfiring spark plugs, lack of power, increased stalling, or increased fuel usage (you will need to get gas much more often).
These are not surefire indications your oxygen sensor needs to be replaced, but a qualified repair shop will certainly be able to tell you for sure, and if you are experiencing any of these symptoms in your vehicle, you likely need to visit a repair shop anyway. The EPA says replacing an O2 sensor can increase fuel economy by up to 40%, however, so it can be an efficient solution if you experience suddenly increased fuel usage. A faulty O2 sensor can also cause your vehicle to fail an emissions test.
What causes an oxygen sensor to fail?
There are several things that might cause your O2 sensor to fail, including but not limited to:
- Contaminated fuel
- An engine that burns oil, which will leave carbon deposits on your O2 sensor
- External contamination like road salt, gasket material, and certain chemicals
- Your sensor could have simply reached the end of its life cycle
What will a new oxygen sensor cost?
Not counting labor (which can vary widely based on the model of your car, due to O2 sensors being located in different places), an O2 sensor can cost anywhere between $100 and $300.