Best O2 Sensors: Monitor Your Engine’s Performance
Monitor the air-fuel ratio and prevent a rich or lean mix in your exhaust with these O2 sensors
The Drive and its partners may earn a commission if you purchase a product through one of our links. Read more.
BY Norah Tarichia / LAST UPDATED ON September 17, 2019
An oxygen or O2 sensor measures the air-to-fuel ratio entering your vehicle’s engine and helps determine if it is starting and running smoothly. It also monitors the emissions from the car’s exhaust and measures the amount of unburnt oxygen. Oxygen sensors are built into vehicles produced after the 1980s, but they wear out just like other components in your car. Here’s a guide of some of the best oxygen sensors that you could use as aftermarket replacements for your vehicle.
Why Trust Us
All of our reviews are based on market research, expert input, or practical experience with most products we include. This way, we offer genuine, accurate guides to help you find the best picks.
Benefits of an O2 Sensor
- Improved engine performance. An oxygen sensor constantly monitors the engine to maximize performance and improve operating efficiency. It controls the fuel and ignition systems to optimize engine power when you want to accelerate and promotes fuel economy when driving at an average speed.
- Reduce emissions. It ensures complete combustion by maintaining the air-fuel ratio at 14.7:1 for a gas engine and 14.5:1 in a diesel engine. Complete combustion prevents harmful gases like carbon monoxide, excess hydrocarbons, and other greenhouse gases from forming in excess.
- Prevent rough idle and engine misfires. Without an oxygen sensor, you may notice that your car rides rough, and you may experience engine problems like a misfire, stalling, or loss of power. An engine sensor prevents these problems by controlling the air/fuel ratio and the engine combustion intervals.
- Prolong the life of your catalytic converter. The oxygen sensor and catalytic converter, which removes harmful emissions from the vehicle’s exhaust, go hand in hand. A defective or lack of an oxygen sensor can cause the premature failure of your catalytic converter, which costs thousands of dollars to replace.
Types of O2 Sensors
Any single or two-wire oxygen sensor without a heater circuit is an unheated thimble. It features a thimble-shaped design on the exhaust and reference side with a zirconia ceramic-coated wire. The lifespan of an unheated thimble is typically 30,000 to 50,000 miles. Unheated thimbles normally fail due to the buildup of soot on the ceramic components.
Any three and four-wire oxygen sensor with a heater circuit is a heated sensor. It carries almost the same design as the unheated sensor. However, the heater increases the operating temperature of the sensor, and it can produce and send voltage signals way faster than an unheated sensor. It also burns off soot deposits during operation, and that’s why heated thimbles last longer.
Bosch is a well-known auto equipment manufacturer that was started by Robert Bosch in 1886. It’s headquartered in Stuttgart, Germany. It produces some of the best automotive parts and power tools and was the first-ever brand to produce oxygen sensors back in 1976. One of its best-selling oxygen sensors is the Bosch Oxygen Sensor.
ACDelco is an old automotive accessory manufacturing company that was founded in 1916. The company is owned by General Motors, and that’s why ACDelco products come as original equipment products for most General Motors vehicles. ACDelco has a great record of manufacturing high-quality oxygen sensors, and one of its cheapest oxygen sensors is the ACDelco Oxygen Sensor.
Denso is an international automotive equipment manufacturer based in Aichi, Japan. The company was founded in 1949, and most of its auto and truck parts are manufactured to OE standards. The company produces products, including condensers, radiators, alternators, starters, spark plugs, and lambda sensors. One of its ultra-power O2 sensors is the Denso Oxygen Sensor.
NGK is a global manufacturer of automotive and technical ceramics products based in Japan. The company has operating centers in the United States, where it chiefly produces its spark plugs and oxygen sensors. It’s one of the pioneer brands in the production of oxygen sensors, and one of its top-quality front oxygen sensors is the NGK Oxygen Sensor.
O2 Sensor Pricing
- Under $50: Most oxygen sensors within this price range will work well with most cars but won’t offer the durability that comes with the high-end versions. They may offer a service life of only 20,000 to 40,000 miles. Also, the heated versions warm up slowly but will help you keep the lean or rich conditions in check.
- Over $50: Most of these high-end versions are built for durability and are guaranteed to offer a significant increase in your fuel savings. Most have steel houses and high-quality plastic, and there’s minimal risk of them melting over time. However, some sensors are highly-priced only for the brand name. You should look into the reliability of the sensor before you buy it.
Choose an oxygen sensor that's compatible with your vehicle’s year, make, and model. Using the wrong engine sensor could damage your catalytic converter. Ideally, you need one that fits at the front of the catalytic convertor and another at the exhaust manifold. Larger vehicles with more cylinders on the engine may need about four sensors.
Look for a sensor that can withstand the high levels of abuse in the exhaust manifold. Stainless steel is the best material since it's durable and rust-resistant. Also, choose a product that’s made of high-quality plastic that resists melting and freezing. You should get at least 60,000 miles from a high-quality oxygen sensor.
The sensor should be accurate at computing air-fuel ratios, detecting the oxygen levels in exhaust fumes, and maintaining communication with the Engine Control Units (ECUs) to optimize combustion. Choose a unit that offers a combination of all these functions.
- Ease of Use: Look for a sensor that's easy to install to avoid paying extra installation fees at a service shop. A single user should be able to click the sensor in place. Choose a sensor with a convenient screw-on design or plug-and-use adapter for a quick and tight fit in the exhaust manifold.
- Wire Length: A short wiring harness is convenient for installation and offers a shorter distance for transmission of signals. A longer wiring harness is more convenient for larger vehicles.
Best O2 Sensor Reviews & Recommendations 2021
- Every time you replace your catalytic converter, also consider replacing your oxygen sensor. This could be after every 60,000 to 90,000 miles. Waiting any longer will reduce your sensor’s ability to capture accurate voltage signals. Replace all the oxygen sensors in your car at the same time.
- You should calibrate a new sensor immediately after installing it in your car. Then recalibrate it at least every 10,000 miles. You can have a mechanic recalibrate the device for you according to the manufacturer’s instructions.
- If you notice an orange color on your sensor, then that’s an indication of lead poisoning. White color is an indication of antifreeze contamination or silicone poisoning. The sensor may also turn black, indicating excessive carbon build-up.
- Inspect your sensors for any signs of wear and tear. Physically inspect the wires after disconnecting them, and take them down to a mechanic to test the voltage.
- Position the sensors at least 24 inches from the exhaust ports. In case the engine runs hot, you want to keep the sensor far from the high exhaust gas temperature that may melt its plastic parts.
Q: What are the signs of a bad oxygen sensor?
A: The check engine light will constantly come on. Also, you will experience poor gas mileage since the fuel delivery and combustion system aren't working at the optimal level. In addition, excess fuel may be injected into your engine system, and it will produce a foul, rotten-egg smell.
Q: Can you clean an O2 sensor?
A: Yes, it’s possible to clean the sensor once you locate it and remove it from the sensor bank. You can put the sensor in a container filled with gasoline, and leave it there for about six hours. The gas will absorb most of the dirt. If you notice some stains on the sensor, you can use a soft-bristled brush to scrub away the dirt.
Q: What is a rich and lean mix?
A: The term is used to describe the imbalance of fuel and oxygen after combustion. The ideal ratio of oxygen to gasoline is 14.7:1. When there’s more gasoline than oxygen we refer to that as a rich mix. In contrast, when there’s more oxygen than the fuel, then it’s a lean mix. Both rich and lean mix is bad for your engine’s performance and the environment.
Q: What happens if I drive without an oxygen sensor?
A: You can drive without an oxygen sensor, but you may notice a significant difference in your fuel mileage. You may spend more on fuel even without changing your daily mileage. Your vehicle will ride rougher, and eventually, the engine may get damaged. In addition, you may get an occasional check engine light, which can be hard to get rid of if you don’t have an engine health monitor.
Our top pick is the Bosch Oxygen Sensor. This sensor will offer you a long service life that’s free of contamination. It has a well-engineered design and is fast and efficient. Moreover, it’s decently priced and works just as well if not better than higher-priced options.
If you don’t want to shell out a lot of money for an oxygen sensor but still want a quality product, then consider the ACDelco Oxygen Sensor. It’s a cheap oxygen sensor with a durable cable, plastic adapter, and a steel housing that will hold up to the harsh conditions of your exhaust.