The umbrella of car maintenance is quite large and includes checking oil and coolant levels, rotating the tires and performing seasonal checkups. Your oxygen sensor is one more device that falls under this maintenance umbrella and needs to be monitored in case it malfunctions.
What is an Oxygen Sensor?
Oxygen sensors were introduced by the Robert Bosch company in 1976 and they fast became one of the most vital technologies responsible for lowering exhaust emissions. Today, these devices are present in a wide range of Asian, European and American cars and their job is to monitor the oxygen levels in the exhaust. Most cars were once equipped with one or two sensors but ever since the Onboard Diagnostics II (OBD2 Scanner) tool was introduced somewhere between 1995 and 1996, the oxygen sensors have doubled in number. The extra sensors were then used to measure the efficiency of the catalytic converter.
The percentage of oxygen found in the engine depends on many factors such as the engine temperature, barometric pressure and altitude as well. Low oxygen levels result in a mixture that is too rich, meaning that there is a large amount of fuel remaining after combustion. High oxygen levels, on the other hand, result in a lean mixture and not enough fuel in the system. Both outcomes are far from desirable and the oxygen sensor knows it, immediately sending a signal to the engine control unit (ECU) to readjust the amount of fuel that is entering the engine.
A faulty oxygen sensor can cause harm to both your vehicle and the environment since more pollutants escape the exhaust when the wrong mixture of fuel and oxygen is present in the engine. The catalytic converter can also suffer major damage because it relies on a specific mixture of oxygen in order to function properly.
How Does it Work?
There are different types of oxygen sensors and these include classic ones that belong to older models, and more advanced ones known as air-fuel ratio sensors or AFR. Wideband and AFR sensors eliminate the lean-rich cycle that used to be the trademark of narrow-band sensors. These modern sensors have the ability to detect the exact amount of oxygen found in the exhaust in real-time and without delay. This feature allows the engine control unit (ECU) to adjust fuel delivery quickly and efficiently no matter the vehicle driving conditions.
Oxygen sensors are also fitted with a heating component that allows their core to reach optimum operating temperature quickly, resulting in faster signals being sent to the ECU.
Location is vital when it comes to measuring oxygen levels and that is why these sensors are placed in two different locations within the vehicle. Downstream oxygen sensors are located between the muffler and catalytic converter while the upstream sensors are located between the exhaust manifold and the converter. The latter are more sophisticated because their job is to send oxygen level signals back to the ECU. The downstream converter has an entirely different role and that is to measure the efficiency of the catalytic converter itself.
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Knowing the symptoms of a bad oxygen sensor will help you take the necessary steps in order to protect both your vehicle and the environment. Below are some of the most common signs that your oxygen sensor is bad:
- Worrisome Check Engine Light
Most car owners are familiar with the orange light in their dashboard and the bad news it may be foreshadowing. Since sensors are directly linked to the engine control unit (ECU), this bright indicator lamp can be a symptom of a faulty oxygen sensor. Before you panic and rush your car over to the mechanic, you need to pull over and take a look at your gas cap. A cracked, loose or damaged cap might be the culprit behind the glowing engine light in your dashboard.
- Poor Mileage
If your engine is suffering in terms of performance and is demanding more fuel than before, you might have a bad oxygen sensor on your hands. This decrease in engine efficiency often translates into more money spent when refueling your car. This is due to the fact that engine performance suffers when the ratio of fuel to oxygen is too rich or too lean. This decrease in efficiency does not happen overnight so it might take you a while to notice that you are paying additional fuel costs at the gas station.
- A Rough Sounding Engine
After years of driving your car, your ears become more skilled at detecting any strange and worrisome engine noises. A rough sounding engine is loud when in idle mode and stops running smoothly. If this is the case when it comes to your car, then chances are that you have a bad oxygen sensor causing mayhem under the hood. A faulty oxygen sensor has a negative effect on the injection timing and combustion levels and can interfere with other engine functions as well. If your car is slow to accelerate or if the engine stops running all of a sudden, then the oxygen sensor may be the culprit in both scenarios.
- Failing the Emissions Test
If your vehicle fails its emissions test, you will be handed a vehicle inspection report that shows you what needs to be fixed. Failed emissions tests sometimes have one thing in common and that is none other than a bad oxygen sensor. The sensor will need to be replaced in order for your car to get retested, otherwise, you will be unable to get it registered. Replacing your sensor is not just about passing the emissions test, it is also about reducing air pollution and protecting your health at the same time.
Nowadays, emissions testing is becoming more popular on a nationwide level with modern testing programs that simulate real life driving conditions used on cars to provide more accurate results. This new technology is proving to be incredibly effective at diagnosing emission problems that used to fly under the radar without detection.
When it comes to fuel injected vehicles, oxygen sensor failure is solely responsible for releasing excessive volumes of emissions into the air and is also the second most noteworthy cause of high emissions in carbureted engines. Date collected by both the Environmental Protection Agency and the California Air Resources Board goes to show that a staggering 42% to 50% of all cars that undergo emissions checks are releasing high levels of hydrocarbons and carbon monoxide into the air.
- Vehicle Age
Car age also matters when it comes to sensor longevity. For example, cars that were manufactured between 1976 and the early 1990s require sensor replacement every 30,000 to 50,000 miles. Heated first generation oxygen sensors installed in mid-eighties to mid-nineties vehicles must be replaced every 60,000 miles. In comparison, modern cars can have their sensor replaced every 100,000 miles.
Oxygen sensors suffer performance-wise when their sensing elements become covered in ash, lead and other combustion byproducts that prevent them from delivering signals to the engine control unit. They are also at risk of failing prematurely if they become contaminated with lead from leaded gasoline or from silicone due to coolant leakage. Outside factors related to the environment can also cause a sensor to fail and these include tar and road salt.
How to Diagnose a Bad Oxygen Sensor?
You can diagnose the problem on your own if you have the right tools at your disposal, and these include an OBD II scanner and a digital voltmeter. A backprobe is used alongside the voltmeter in order to directly test the oxygen sensor while it remains connected to the vehicle. All you need to do is examine the wires encompassing the sensor to check if they are still in good condition. Once you complete this step, you will need to start up the engine and wait for it to heat up. Driving your car for around twenty minutes will sufficiently heat up the engine. Once it is sufficiently heated, you can switch it off in order to carry out the diagnosis.
- Depending on where the faulty sensor is, you will need to lift the car using a floor jack before adding a couple of jack stands to safely prop up the vehicle.
- Practice caution when connecting the meter. The exhaust manifold and pipes will be scorching hot and you may get burned as a result.
- The meter comes with a red and a black probe. If the sensor has two or three wires, you will need to connect the red probe to the signal wire and attach the black probe to a good ground on your engine. However, if the oxygen sensors has four wires you will need to connect the black probe to the sensor’s ground wire. Make sure you have your vehicle repair manual on hand in case you need further guidance during this process.
- Once you establish all connections, start the engine and check the voltage signals on your voltmeter. The sensor voltage needs to be within the 0.1 – 0.9 V range. A faulty sensor will generate an entirely different signal that is either too high or low.
There are two more tests that enable you to double check the sensors. The first one allows you to examine the oxygen sensor’s response to lean fuel condition, and the second test allows you to check its response to a rich fuel condition. If the sensor in question responds correctly to both tests, then there might be another component responsible for the drop in fuel efficiency.
Replacing the sensor can be done using the following tools:
The first thing you need to do is make sure that the ignition switch is off before disconnecting the car battery.
Next, you need to remove the oxygen sensor connector. This requires getting rid of the security clip first using a screwdriver in order to push down the plastic tab and smoothly pull out the wiring harness.
Unscrew the oxygen sensor using an adequately sized wrench. Most sensors require an SAE wrench to facilitate the task of removing them. Working with the right wrench can make a big difference when dealing with sensor cables and can come to the rescue if the sensor happens to be stuck in its place. It is worth mentioning here that the sensor operates in a hostile environment and much like a spark plug, it is mounted in place by threads and screws. The anti-seize grease is usually added to the threads to make the removal process easy. However, this substance eventually loses its effectiveness over time, resulting in a sensor that is impossible to unscrew using ordinary tools. This can turn an easy fifteen minute task into a long and complicated ordeal. If you find yourself facing a similar scenario, then it is better to hand this over to a professional.
Once your old sensor has been successfully removed, you may proceed to install the brand new oxygen sensor. The new sensor should be handled with the utmost care to prevent the tip from being contaminated. Modern sensors are sold with their very own grease which is then applied to the new sensor threads only. Using the grease will prevent the sensor from fusing with the exhaust pipe. Just make sure that the grease does not come into contact with the sensor head since this can damage the device.
Once the above step is completed, reconnect the battery and hand tighten the sensor in the exhaust bung. The tip needs to be kept away from the sides during this process. Use a socket wrench to secure the oxygen sensor in place and then reroute the wire and attach the connector.
If the -Check Engine Light- is still on, you will need to clear the ECU memory using your OBD II scanner. Erasing the memory will remove the fault code from the system. You will be required to place your vehicle in the Key On -Engine Off (KOEO) mode during this step.
Finally, take your car out for a drive and test out your newly installed sensor.
In summary, keeping the oxygen sensor in mint condition and replacing it during the designated change intervals contributes to a better fuel economy and allows you to save money on fuel. It also means cutting back on exhaust emissions and reducing the risk of costly damage to the catalytic converter. Peak engine performance is one more thing to look forward to once you change your bad oxygen sensor. All in all, this is a win-win situation for you and the environment.
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