Blair Lampe View All

Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter.  In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.


How to check for bad O2 sensor?

If there is any fault in the oxygen sensor, it usually illuminates the engine check light in the instrument cluster. You can diagnose the problem by connecting an OBD2 scanner to your vehicle. If you see any error code from P0130 to P0135 or from P0150 to P0155, it indicates a problem with the upstream oxygen sensor. You can also perform a continuity test on the connector of the sensor with a multimeter to check if the heater circuit is broken.

3. Rough engine idle and misfires

As your oxygen sensor is going bad you may notice your vehicle is running rough, misfiring or running irregularly while idling. You may also observe other engine performance problems, such as loss of power, hesitation, or stalling. Since the oxygen sensor output helps control engine timing, combustion intervals, and the air to fuel ratio, a bad sensor can disrupt these engine functions, causing a rough or irregular engine idle and other engine-related issues.

What is an Oxygen Sensor?

The oxygen sensor is an electronic device installe

The oxygen sensor is an electronic device installed in your car and measures the amount and concentration of oxygen in the exhausts. It is also known as a lambda sensor.

Advanced automotive technology is capable of producing the most efficient oxygen sensors. The lambda sensor is an essential component of all vehicles manufactured after the 1980s. The main function of the lambda sensor is to collect data on how much oxygen is available for combustion and send it to the engine management system.

The system then uses the data for fuel injection and other purposes.

Oxygen sensors usually do not fail completely, but their efficiency decreases over time.

Next Step

Schedule Exhaust and Emission System Inspection

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2. Bad Gas Mileage

If you’re spending more money than usual on fuel, your vehicle could have a bad oxygen sensor. Engines are less efficient when the oxygen to fuel ratio is too rich or too lean. Oxygen sensors usually become less effective over time, so you’ll probably notice a gradual increase in costs instead of a sudden increase.

What causes O2 sensors to fail?

All O2 sensors fail over time since it is a wearing part. There is no fixed time limit for when they fail, but they typically last over 100,000 miles. However, they can fail much sooner due to contamination. For example, due to silicates entering the exhaust system after coolant burns in the engine due to a leaky head gasket, or phosphorus from excessive oil consumption due to worn piston rings or valve seals.

Common Signs and Symptoms of a a Bad Oxygen (O2) Sensor

Seeing as how the O2 sensor plays such a large role in ensuring that the engine runs properly, it is easy to understand how many of the signs and symptoms of O2 failure are related to the engine’s suboptimal performance. However, there are other signs and symptoms of sensor failure as well.

Emissions Test Failure

The O2 sensor serves as an emissions device first and foremost. If it does not function properly or is completely broken, your vehicle will not be able to pass an emissions test. Not all states require emissions testing and some states that do only require them for parts of the state. All this to say, an emissions test failure will not always detect O2 sensor malfunction since it is not universally required.

Poor Fuel Economy

A drastic drop in fuel economy is one of the telltale signs of oxygen sensor failure. The EPA estimates that fuel economy could drop by up to 40% when an O2 sensor fails. This is because the necessary communication of the proper air-fuel mixture within the engine is either hampered or incorrect. The result is the drastic loss of efficiency.

Engine Overheating

One of the less common issues associate with O2 sensor failure is engine overheating. This occurs when too much fuel is consistently used for combustion. Since the oxygen sensor is the primary regulator of the air-fuel mixture, overheating will continue occurring until the sensor is replaced.

Thankfully, there are many other systems at work in most vehicles. These systems can usually keep the overheating issues at bay for a while, but consistent overheating will eventually cause problems, and the other vehicle systems will not be able to keep up. 

Rough Idle

A rough idle is probably going to be one of the first signs of O2 sensor failure. It is the direct result of a failing or already failed sensor since the optimal combustion mixture can no longer be controlled. Two phrases used for this are “running rich”, and “running lean”. Running lean means an excess of air within the air-to-fuel ratio, and running rich means an excess of fuel used within the ratio. 

Both issues lead to improper combustion which can cause engine hesitation as it struggles to nail down the combustion “sweet spot.”

Poor Engine Performance

If your vehicle’s engine is suffering at idle, it logically follows that the issues will translate well when you start moving. Overall engine performance when you are driving, including acceleration, staying at a consistent speed, and hesitation at any time are all the result of the same issues that cause rough idling. 

Even though poor engine performance, rough idling, and engine overheating are all very similar and somewhat connected symptoms of a bad O2 sensor, each represents an escalation in severity and the greater potential for overall engine damage. Poor engine performance and overheating can be caused by other things, but experiencing any of these signs and symptoms should warrant a trip to the mechanic. 


An engine misfire – incomplete or total lack of combustion within one or more combustion chambers – is a two-headed monster. It can be the cause of poor overall engine performance and rough idling or it can be the culmination of prolonged engine performance issues. Either way, a misfire is a sure sign that your vehicle needs to be inspected. 

It can sometimes be difficult to diagnose an engine misfire since it usually feels like hesitation or an overall lack of power. This is why it is so important to have your vehicle inspected if it starts to feel abnormally sluggish.

Vehicle Stalling

Vehicle stalling is even one step higher than an engine misfire. With a misfire, an engine can still work and power a vehicle, albeit on a lower level than when it is running well. Vehicle stalling usually occurs when a misfire is so bad that the engine can no longer sustain itself with the remaining working pistons. Of course, a failed O2 sensor, both directly and indirectly, can cause engine stalling in worst-case scenarios.

Again, many of these issues, including stalling, can be signs of other issues. A good way to better pinpoint the O2 sensor as the cause of poor overall engine performance is to replace your vehicle’s spark plugs. They are a very common cause of these issues as well, and if a change does not fix the issue, it is a good sign that the oxygen sensor might be the culprit.

Check Engine Light

As with most vehicle system issues or failures, the check engine light can come on in the event of an O2 sensor failure. But, unlike many other systems, oxygen sensor failure does not always directly cause the check engine light to illuminate. More often, other systems fail as a result of the O2 sensor failure that causes the check engine light to illuminate. 

When this happens, it should not be ignored. Most automotive retail locations offer free diagnostic testing, a good option for anybody who does not have their own OBD scanner.

Why Do O2 Sensors Go Bad?

O2 sensors degrade for a variety of reasons from being contaminated over the years with harsh fuel additives to oil leaks. Generally O2 sensors have a maximum lifespan of about 100,000 miles at which point they need to be replaced. 

How Long Do O2 Sensors Last?

There are a ton of resources online with varying responses to this question. Summing up these references, O2 sensors can last between 30,000 and 100,000 miles. But again, the longevity of oxygen sensors depends on whether a vehicle is new or has seen better days. Vehicles manufactured in the last 15 years are observed to have O2 sensors lasting 30,000 to 50,000 miles or three to five years before necessitating replacement. Conversely, O2 sensors in modern cars have sensors built to last 60,000 to 100,000 miles or seven to ten years.

5. Rough Idling

As we mentioned above, your car, truck, or C/SUV might lose power if the oxygen sensor is acting up. It might also idle roughly, or give you a combination of signs such as idling roughly at a red light and then hesitating to go and speed up once the light turns green. This is also a sign of fuel problems.

How Long Does It Take To Have An O2 Sensor Replaced

The O2 sensor is fast and simple to replace. The entire replacement generally won’t take longer than 10 minutes to complete. When compiled with resetting the computer, the entire repair should take no longer than half an hour. This makes the labor costs on this repair very low. The part is also inexpensive making it one of the better repairs you will eventually need to make on a car. 

As O2 sensors age, they degrade thanks to outside contaminants. Typically a fuel sensor that was manufactured any time in the last 15 years will last from 60,000 to 100,000 miles before needing to be replaced. When you see the symptoms of an illuminated check engine light, sulfur smell, black smokey exhaust, poor gas mileage, rough idling or engine misfires, be sure to take your car to a trusted mechanic immediately! Luckily, this repair won’t run you more than $200 to fix. 

If you are concerned for the health of your vehicle in this area, call a mechanic and schedule an exhaust and emission system inspection. 

If you have an extended warranty through PMC check out your policy to see if you are covered for O2 sensor replacement. You could pay next to nothing for your repairs with your policy through Protect My Car. 

Protect My Car provides consumers with extended auto warranty plans that have real coverage for vehicles that are no longer covered by their manufacturer’s warranty. Whether your vehicle was purchased new or used, if your manufacturer’s warranty is about to expire, or has already expired, an extended auto warranty plan can save you thousands of dollars in repair bills. Since the majority of vehicle repairs happen 3-5 years after the original purchase date, which many times is outside of the manufacturer’s warranty coverage period, leaving you responsible for paying the full repair bill. However, when you purchase a policy from Protect My Car, you could pay as little as $100.00 for your major repairs. That’s a lot of savings!


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