Having the check engine come on is not a pretty sight. That warning sign is there to tell you that your vehicle is due for service or repairs. In general, this warning light comes on when your vehicle’s emission is malfunctioning. One of the main reasons the check engine light comes on is because of a faulty O2 sensor. What is this oxygen sensor and what is its purpose? Read on to learn its importance and to know when it is time to get service or repairs.
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The oxygen sensor is one of the most important parts of your vehicle’s emissions system. It is usually placed on the passenger side of the vehicle. The sensor is mounted directly onto the exhaust pipe close to the catalytic converter. It measures the ratio of oxygen in the car’s engine. The internal combustion in the car happens when gasoline is burned. Most vehicles require a ratio of 14 grams of oxygen per gram of gas to properly burn gasoline. The oxygen sensor helps keep that balance under control. This is why when it malfunctions your car will use too much gas causing your vehicle to lose up to 40 percent of its fuel efficiency.
An engine is said to be running lean when the vehicle has more air than necessary. On the contrary, the engine is running rich when the engine doesn’t get sufficient air. When your car jerks or hesitates when accelerating, you're probably having a lean engine. A rich engine mixture is not also good since it makes the vehicle run hot and creates pollution. Engine damage and poor fuel economy can result in both conditions.
The sensor measures oxygen levels being emitted by the engine. The information obtained is utilized by the Powertrain Control Module (PCM) to determine the proper air to fuel ratio for the engine in real time. A car may have one, two, three or even four O2 sensors, depending on the make, model and engine type.The sensor also keeps the fuel injection and engine timing run efficiently which helps with emissions control. It sends the data to the car's PCM to keep the optimal air to fuel ratio for the engine. A faulty oxygen sensor will have negative effects on the engine’s performance and on environmental emissions.
Here are signs of a failing oxygen sensor:
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Check Engine Light Lits Up
The Check Engine list is the first line of defense. It will turn on when you have a faulty or failing oxygen sensor. Have your car inspected by a professional automotive technician as soon as this light illuminates. The Check Engine Light can turn on for more than one reason, so it is best to have a professional inspect it to identify the exact cause. If you have a high mileage car, it is most likely a bad oxygen sensor that has to be replaced.
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Poor Gas Mileage
A faulty oxygen sensor will throw off fuel-delivery and fuel-combustion systems. It disrupts the air to fuel ratio mixture and it can also cause too much fuel to get injected to the engine. These two conditions reduce fuel efficiency. If you suddenly find yourself having to fill up on gas more often than your usual, best to have a record of the number of gallons you fill up and the number of times you have to fill up. If it is above your average consumption, then it is best to have a professional mechanic inspect your oxygen sensor.
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Engine is running rough and misfiring while idling.
A failing oxygen sensor can cause your vehicle to run rough, misfire or run irregularly while idling. The oxygen sensor helps combustion interval, engine timing and air to fuel ratio and when the sensor malfunctions these engine functions are affected which result in a rough or irregular engine idle.
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Failing an emission test.
A bad oxygen sensor is one of the most common reasons for failing an emission test. So better have your mechanic checked your sensors first before doing an emission test to save time and money.
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Rotten Egg Smell
If your car smells like rotten eggs or burning sulfur, then it could be that your O2 sensor is failing or an issue with the catalytic inverter. When your oxygen sensor malfunctions it could lead to a poor fuel to air mixture and when the balance is not correct it can damage the catalytic converter in the exhaust system.
When To Replace Oxygen Sensors
For vehicles that are manufactured within the last 15 years, the oxygen sensor must be replaced every 60,000 to 90,000 miles. Older vehicles will need to have a replacement at 50,000 to 70,000 miles. To be sure, you can check the manufacturer’s recommended service for the most appropriate guidelines. Remember you do not need to wait for the signs of a failing oxygen sensor to decide that it is time to replace it. Experts recommend replacing them at specific mileage intervals for preventive maintenance. This will help maintain your engine’s peak performance.
Sensors like other parts of the car are a wear item and do fail over time. When you replace a faulty oxygen sensor, the level of emissions your car puts into the atmosphere will be reduced and at the same time, your car’s engine will be running smoothly and efficiently. It will also make your engine last longer.
Diagnosing a faulty oxygen sensor and replacing it is fairly easy. Most of the time, you can no longer repair a bad O2 sensor. Because of the technology and materials of its housing, it must be replaced when it becomes faulty. You can find some DIY places which can show you how you can clean the oxygen sensor so you can extend its life for a few more miles but in the end it would just be a waste of time and effort for you are only delaying what is bound to happen plus cleaning the sensor does not guarantee that it would fix the issue. And you may damage the sensitive technology. It is still best to have a professional mechanic fix it instead of taking a risk with a DIY job that does not guarantee a fix.
The truth is most motorists do not replace their oxygen sensors unless a problem arises and the Check Engine illuminates. But if you have a clear understanding and knowledge of what a failing O2 sensor does to your vehicle, you will probably replace it right away. You will still save more money in the long run since a failing oxygen sensor can significantly reduce your fuel mileage and your engine’s performance.
Oxygen Sensor Maintenance Tips
The oxygen sensor has to endure extreme heat and harmful gases every day of its running life. This modest part of a vehicle plays a significant role on a vehicle’s emission, fuel economy and driveability yet only few motorists actually know what role they play. And even those who know its functions are less likely to identify the signs of a worn-out, failing or completely dead oxygen sensor. So you cannot count on most motorists to actually set an appointment for his vehicle to get an oxygen sensor service. When an O2 sensor malfunctions or begins to fail, you might think your car just needs a tune-up and this actually makes sense since the signs can be very similar to what you would typically notice when ignition parts begin to fail or become worn.
Newer versions of oxygen sensors have a longer lifespan but like their predecessors they also have limited lifespans. This is why you should include O2 sensor replacement intervals among your vehicle maintenance schedules. Most car makers today have changed that strategy and made O2 sensors “replace when they fail” components. An oxygen sensor fails for a variety of reasons including the sensor exceeding its design-life expectancy, too much burning of oil causing sensor carbon fouling, contaminated sensor due to antifreeze leak or by silicone found in spray chemicals, gasket material, etc., external contamination by other vehicle chemicals applied near the oxygen sensor, or lead fouling due to fueling with contaminated/leaded gas.
Sensor Inspection & Testing
The O2 sensor should be also checked every engine performance service or whenever there is a noticeable change in its performance. A visual inspection is not enough to verify the functionality of the O2 sensor. It would need to undergo an oscilloscope test. This will provide a more accurate diagnosis as it can check the sensor’s ability to respond to changes in exhaust oxygen content and can measure its response time.
Here’s how you can check an O2’s ability to respond to rich and lean conditions:
- Connect your oscilloscope leads to the oxygen sensor circuit. If you have a three- or four-wire heated oxygen sensor, you may need to bridge the connector leads and tap them into the signal wire using an appropriate test probe at the connector plug.
- Turn on the engine and warm it to operating temperature since O2 sensors run properly only when they’re at least 350/F. Run your engine at about 2500 rpm for a couple of minutes to heat up the O2 sensor.
- Keep your engine speed at a steady, high idle between 1200 and 2000 rpm.
- Do an artificial drive: for the system rich, use propane; for lean, open the brake booster hose while observing the oscilloscope voltage reading. The range should .800 to .900 volt for full rich to .100 to. 200 for full lean.
The minimum and maximum sensor voltages are only one aspect to look at for O2 sensor’s performance. It is also important to take note how fast these transitions occur to determine the health of the oxygen sensor. Rich-to-lean and rich-to-lean transitions should transpire in 300mS or less, when it is greater than that it means your sensor might be worn or contaminated. An oscilloscope or graphing multimeter is needed for this test.
There are a few vehicles that come with a new type of oxygen sensor referred to as air/fuel ratio sensor. This type of sensor produces a linear voltage signal unlike conventional sensors which produce toggling voltage. A different testing method is used for this new type of O2 sensor. What makes this type better than the conventionals ones is that they allow more accurate monitoring and correction of the fuel mixture ratio. It is predicted that this type would be used more in the future.
All O2 sensors are now heated. Heating the sensor makes it last longer partly because it can be placed further below in the exhaust system. It also protects the sensor from thermal shocks from the heating and cooling cycles of the engine. On top of that, heated sensors attain operating temp quickly and start producing a sensing voltage without waiting for the heat of the exhaust to heat them up.
Heated O2 sensors have smaller slots in the protective tube at the head which limits the amount of exhaust that gets into the sensing tube and limits any contaminants that can get into the sensor reducing its response. As a result, a heated oxygen sensor can last up to 100,000 miles or more.
Can You Continue Driving With A Failing O2 Sensor?
Yes, you can if you can still start your engine. However, do not ignore this problem for more than a couple of days as it might cause bigger car problems and can risk your safety. A faulty oxygen sensor could lead to poor gas mileage, high pollution, and cause sluggish and rough driving with stalls. Ignoring it for months may also lead to serious engine and catalytic converter problems that cost thousands of dollars to repair or replace. Thus, you must have your oxygen sensor inspected as soon as you can by going to a mechanic. Or you can also do the diagnosis if you have the tools. There are times when a trouble code saying that the oxygen sensor is not working properly can be fixed by cleaning the oxygen sensor or replacing a pipe connection.