O2 sensors are required on all vehicles produced after 1981. Many modern cars include several O2 sensors because of the ODB-II requirements, which apply to vehicles made in 1996 and later. Some automobiles even have four oxygen sensors. A second oxygen sensor that is situated below the catalytic converter is a requirement for vehicles built in 1996 and later. This O2 sensor keeps an eye on the catalytic converter’s performance.
The catalytic converter is not functioning properly if the sensor following the catalytic converter only exhibits minor variations from the reading on the first oxygen sensor. Up to four O2 sensors may be present in contemporary V-6 or V-8 engines, one after each catalytic converter and one in each cylinder bank. Your car could face severe engine issues if either the oxygen sensor in the cylinder block or the catalytic converter malfunctions.
You might be curious as to when to consider replacement because oxygen sensors are crucial to the performance and emissions control of your engine.
In This Article...
Symptoms of a Bad Oxygen Sensor
First and foremost, it’s crucial to realize that an OBDII code by itself does not indicate that an oxygen sensor has failed. Sensors merely provide data. For instance, an oxygen sensor that detects a lean fuel combination will undoubtedly trigger a code. There is no need to replace this sensor because it is functioning properly.
There are various OBDII codes in particular that will be activated if a malfunctioning or dead sensor is the problem (more on this in the following section). A malfunctioning sensor will thus frequently cause the car to physically exhibit the symptoms.
A drop in fuel economy may be a clear indication that an O2 sensor is not functioning properly. A gasoline combination that is either too low or too rich can produce this.
A/F ratio swings of this magnitude indicate a malfunctioning upstream or control sensor. The downstream or diagnostic sensors won’t result in such a problem because they just keep track of the exhaust leaving the catalytic converter.
Additionally, a misfire, a rough idle, and/or hesitancy when attempting to accelerate are signs of a malfunctioning oxygen sensor. However, keep in mind that these problems might also have unrelated root causes that have nothing to do with an automobile’s oxygen sensors. Therefore, none of them by themselves would be sufficient to replace one. It is frequently necessary to combine an OBII warning with engine performance difficulties and a physical examination of the sensor in order to reach an accurate diagnosis.
Common O2 Failure Causes
Three main causes of oxygen sensor failure are age and heavy mileage, an internal pollutant (poisoning), or an electrical problem.
Every 30,000 miles, one or two wire unheated oxygen sensors should be checked or replaced. These sensors are made to allow a significant volume of exhaust to come into touch with the active ceramic element because they are totally dependent on hot exhaust gas to reach their operational temperature.
Due to their internal heat source, heated oxygen sensors can be put much farther downstream than unheated sensors, making them less susceptible to contamination. Every 60,000 miles, heated sensors should be checked out or replaced. While heated oxygen sensors can be used in locations that are safer than unheated versions, they contain numerous circuits that make them susceptible to electrical problems. A sensor won’t work properly if the heater circuit in it malfunctions. In fact, heater circuit problems are a frequent cause of OBDII codes.
All oxygen sensors must be exposed to a continuous stream of hazardous exhaust gases, intense heat, and high velocity particles in order to function. As a result, their effectiveness will unavoidably decline over time.
Oxygen sensors may become tainted with substances from the engine. Leaded gasoline and exhaust from an excessively rich fuel mixture might contaminate an O2 sensor. The similar result may be obtained from silicone or antifreeze residue left over from damaged gaskets. The sensors shown below need to be replaced since they have been contaminated.
Numerous sensors degrade frequently as a result of carbon buildup from a heavy fuel mixture. This could be caused by a number of things, such as a blocked air filter or a fuel injector that is leaking or broken.
If antifreeze gets into the combustion chamber, it can seriously damage a sensor. This may occur as a result of an intake manifold gasket leak, a leaking cylinder head gasket, or a warped or cracked cylinder head.
An oxygen sensor’s head can turn white due to silicone poisoning, as seen in the image on the left. The use of an inappropriate silicone gasket sealant on the engine is the most frequent cause of this issue.
An oxygen sensor will suffer if inappropriate (leaded) fuel is used. Even though this is a rare event, it is useful to understand how leaded gasoline affects sensors.
The oxygen sensor will not come out.
Use a strong penetrating lubricant to thoroughly coat the sensor thread region. By heating up the bung, starting and revving the engine should help to further loosen the sensor. Try an O2 socket if you are currently using an open end wrench. If that doesn’t work, try using your socket and a long ratchet or breaker bar to produce greater torque. If the problem persists, heat the bung with a torch until it turns cherry red, then remove the sensor. Use a thread cleaner to clean the bung threads after the sensor has been removed. The threads may need to be mended in some circumstances. A thread repair kit (Walker Part # 88-832) can be used for this. Never remove an O2 sensor with an impact wrench because you risk stripping the threads in the bung. Walker carries a full line of oxygen sensor bungs and plugs in case a problem arises that calls for the replacement or addition of a bung.
Are the rear oxygen sensors really necessary?
The function of the downstream sensors is to keep an eye on the catalytic converter’s performance and overall health. Removing them will disable this function and result in a malfunction indication light (MIL) or CEL (check engine light) on the car.
I am getting a CEL/MIL and a . . . code. Do I need to replace the oxygen sensor?
No, not always. The data that the oxygen sensor collects is simply reported. For instance, you can have a vacuum leak or a bad fuel injector if you receive a lean mixture code. The oxygen sensor cannot be replaced to resolve this issue. You’ll simply receive the same code once more.
Do I need to replace all of the sensors at once?
O2 sensors should ideally be changed in pairs. For instance, you should replace the downstream right sensor if you replace the downstream left sensor.
On the majority of cars made after 1996, the ECU will set a code for the other sensors if one sensor is replaced, particularly the front engine monitoring sensor. This is due to the fact that new sensors switch activities considerably more quickly than do older, more seasoned sensors. On the majority of vehicles, the code is likely to be set between 30 and 60 days AFTER the first sensor replacement.
What is the life expectancy of an oxygen sensor?
Every 60,000 miles for heated oxygen sensors and every 30,000 miles for unheated oxygen sensors, respectively, should be the time for inspection or replacement.
How can I test an oxygen sensor?
By first locating the signal line on the sensor, you may test the O2 sensor in a car. The voltage will also oscillate between 200 and 800 millivolts, or.2 to.8 volts on your meter, when you use a voltmeter with the scale set to 1 volt. Your sensor has failed if the reading is stuck in one place or switches unusually high or low. It is important to have your vehicle tested at a reputable facility if your results are ambiguous.
A second approach is to directly link some of the several testers on the market to the oxygen sensor. Although this method is less precise, it can identify some sensor malfunctions.
What is a California emissions sensor? How do I know if I need one?
A California emissions O2 sensor is intended for automobiles built to comply with California emission standards. A sticker identifying these vehicles ought to be placed on the driver’s door jamb or beneath the hood.
What are the symptoms of a failing oxygen sensor?
A faulty sensor will typically result in low gas mileage, stalling or reluctance, and a CEL/MIL. The oxygen sensor is not the only reason for these symptoms, though.
What is an Oxygen Sensor?
In order to track how much unburned oxygen is present in the exhaust as it leaves the engine, oxygen sensorsalso known as “O2 sensors” because O2 is the molecular formula for oxygenare put in the exhaust manifold of the vehicle.
These sensors inform your car if the fuel mix is running lean (too much oxygen) or rich (insufficient oxygen) by monitoring oxygen levels and delivering this information to your engine’s computer (too much oxygen). Your car needs the right air-to-fuel ratio to continue operating as smoothly as it should.
Because the O2 sensor is crucial to engine performance, emissions, and fuel efficiency, it’s critical to comprehend how they operate and make sure yours is in good operating order.
Where are Oxygen Sensors Located?
Variables affect how many oxygen sensors a car has. Oxygen sensors must be installed upstream and downstream of each catalytic converter in vehicles manufactured after 1996. As a result, whereas the majority of vehicles only have two oxygen sensors, those V6 and V8 engines with dual exhaust have four oxygen sensorsone on each engine bank, one upstream and one downstream of the catalytic converter.
What Does an Oxygen Sensor Do?
The amount of oxygen in the exhaust is measured by the vehicle’s 02 sensor, which then provides feedback to the computer in your car. The computer then modifies your air/fuel mixture using this information.
When oxygen sensors get hot, they start to generate their own electricity (approximately 600F). A zirconium ceramic bulb is located on the tip of the oxygen sensor, which plugs into the exhaust manifold. A porous layer of platinum is applied to both the inside and the exterior of the bulb, acting as the electrodes. Through the sensor body, the interior of the bulb is internally vented to the atmosphere outside.
The difference in oxygen concentrations between the bulb and the atmosphere outside causes electricity to flow through the bulb when the outside of the bulb is exposed to the hot exhaust fumes.
The voltage is relatively low, around 0.1 volts, if the fuel ratio is lean (not enough fuel in the mixture). The voltage is relatively high, around 0.9 volts, if the fuel ratio is rich (too much fuel in the mixture). The oxygen sensor generates 0.45 volts when the air/fuel mixture is stoichiometric (14.7 parts air to 1 part fuel).
The Upstream Oxygen Sensor (Oxygen Sensor 1)
In relation to the catalytic converter, oxygen sensor 1 is the upstream oxygen sensor. In order to control the air-fuel mixture, it measures the air-to-fuel ratio of the exhaust leaving the exhaust manifold and transmits high- and low-voltage signals to the powertrain control module. The powertrain control module adjusts the amount of fuel in the mixture when it detects a low voltage (lean) signal. The powertrain control module leans the mixture by reducing the amount of fuel it provides to the mixture when it receives a high voltage (rich) signal.
A closed feedback control loop is when the oxygen sensor input is used by the powertrain control module to control the fuel mixture. The catalytic converter can reduce emissions by keeping the overall average ratio of the fuel mixture in the right balance by continuously switching between rich and lean as a result of this closed-loop function.
However, the powertrain control module switches to open loop operation when an engine is started cold or if an oxygen sensor fails. The powertrain control module mandates a fixed rich fuel mixture in open loop operation even when the oxygen sensor is not sending a signal. Fuel consumption and emissions rise as a result of open loop operation. In order to reduce the amount of time spent in open loop operation, many contemporary oxygen sensors have heating components to help them quickly reach operating temperature.
The Downstream Oxygen Sensor (Oxygen Sensor 2)
In connection to the catalytic converter, oxygen sensor 2 is the downstream oxygen sensor. To check that the catalytic converter is operating properly, it measures the air-fuel ratio leaving the converter. The powertrain management module continuously switches between rich and lean air-fuel mixes as a result of the input from the upstream oxygen sensor while the catalytic converter attempts to maintain the stoichiometric air-fuel ratio of 14.7:1. (sensor 1). As a result, the sensor 2 downstream oxygen sensor should generate a consistent voltage of about 0.45 volts.
Symptoms of a Bad O2 Sensor
Different diagnostic trouble codes (DTCs) may appear when a 02 sensor fails. The majority of the time, a bad O2 sensor will cause the check engine light to come on and leave a fault code that an OBD2 scanner like FIXD can read. This fault code will indicate the cause of the failure before the diagnosis is continued.
A malfunctioning O2 sensor may exhibit the following symptoms:
- Rich or lean operating conditions
- sluggish acceleration
- engine stutter
- black exhaust fumes (rich running condition) Black smoke coming from the exhaust is extra fuel.
- erratic idle
- automobile stalling
- Fuel efficiency decline
Checking the operation of your O2 sensor using a scan tool is the first step in figuring out if you have a defective oxygen sensor or a lean or rich running condition.
How to Test Oxygen Sensors
It’s critical to ensure that the O2 sensor is functioning properly because it helps maintain your engine operating as effectively and cleanly as possible. The normal lifespan of an oxygen sensor is between 30,000 and 50,000 miles, or 3-5 years. Newer sensors can survive much longer with the right maintenance and care. Depending on whether you DIY or visit a shop, the cost to replace an oxygen sensor ranges from $155 to $500.
With a voltmeter or an OBD2 scan tool like the FIXD Sensor, you can test the oxygen sensor at home. To view the voltage and response time of your O2 sensors, navigate to the live data feed within the FIXD app.
A front (upstream) O2 sensor 1 that is working properly should typically be transitioning from rich to lean at a fairly constant rate, forming something resembling a wave. The O2 sensor’s voltage output should range from 0.1V to 0.9V, with 0.9V being rich and 0.1V being lean. Your O2 sensor is working properly if your results fall within this range.
If everything is running smoothly, the catalyst monitor rear (downstream) oxygen sensor 2 will be circling around half a volt. However, depending on the manufacturer, this measurement can vary.
Additional O2 Sensor Testing Tips
If the O2 Sensor does not react to testing promptly:
It may be a “lazy O2 sensor” issue if there are other symptoms without a fault code and the sensor appears sluggish or slow to react during testing.
If there is richness or leanness in the O2 Sensor voltage:
To ascertain if the problem is with the oxygen sensor or the air-fuel combination, try introducing the opposite scenario. For instance, if your O2 sensor is sticking lean, add fuel and see how the condition changes. If the O2 sensor is on the rich side, experiment with adding more oxygen or a vacuum leak to see how and if the sensor reacts.
Stay in the Know with the FIXD Sensor & App
You can take charge of car maintenance and save thousands of dollars with the FIXD car scanner and app. To help you prolong the life of your car and prevent needless upsells, FIXD keeps you updated with real-time data on gasoline trims, oxygen sensor levels, battery voltage, and more. These notifications are provided directly to your phone. Find out more information about the FIXD OBD2 scanner and app now!