While you’ve probably heard the term “oxygen sensor” before, you may not know what it is or why you need one. This component is one of the most important sensors in your vehicle, and it helps to maintain engine performance and environmental safety.
Keep reading to learn how an oxygen sensor works, the symptoms of a failing oxygen sensor, and why driving with a bad O2 sensor is a bad idea.
What Does an Oxygen Sensor Do?
An O2 sensor measures how much oxygen is present in the exhaust fumes to determine the workload of the engine.
The operation of gas engines involves the explosion of a mixture of air and fuel. These two substances must be combusted in well-defined proportions. If the proportion of fuel to air is subpar, the engine is said to be “rich” from a lack of oxygen or “lean” due to an excess amount of oxygen. Both scenarios can cause detrimental consequences to the engine.
An oxygen sensor identifies rich or lean mixtures and sends a command to your Powertrain Control Module (PCM) to balance the ratio. The PCM will subsequently adjust the amount of fuel directed to the engine.
Many typical vehicles have at least 2 oxygen sensors. The second one measures oxygen in the exhaust flow, but does so only after the exhaust gases have already undergone oxygen measurement using the catalytic converter.
The second O2 sensor is installed after the catalytic converter so that it may assess its performance in converting exhaust gas into less noxious emissions. The unoxidized hydrocarbons, or rather the unneeded exhaust fumes, that motor vehicles release can be converted by the catalytic converters to control the release of dangerous gas emissions.
Oxygen Sensor: How it Works
Most oxygen sensors send an electric signal to the car’s Powertrain Control Module indicating how rich or lean the air-fuel mixture needs to be. To accomplish this task, every second measures the exhaust oxygen content is measured and compared to the surrounding atmosphere.
Oxygen sensors are usually bolted directly on the pipeline of the exhaust system. One section of the O2 sensor is in the hot exhaust while the other section is exposed to ambient air.
The chemical reaction that takes place due to the difference in oxygen concentration in the two sections produces an electric charge of between 0.1 and 0.9 volts. If the O2 reading is above 0.45 volts, that means the fuel is too rich. If it goes lower than 0.45, that means the fuel is too lean.
Location
Most vehicles now possess at least two oxygen sensors integrated within the exhaust system. One of these sensors is positioned upstream of the catalytic converter, while the other one is located downstream of the converter.
Vehicles equipped with a “V” type engine are usually provided with more than four oxygen sensors, where the units on each side of the engine bank are two.
Lifespan
Broadly speaking, the functional life of an oxygen sensor should be between 40,000-80,000 miles. However, it is not unusual for an oxygen sensor to operate longer than 100,000 miles.
Some oxygen sensors, generally low-cost aftermarket models, sensors that have had some sort of contamination, or experts of other kinds of sabotage, do fail as early as 30,000 miles.
Bad O2 Sensor Symptoms
The faulty oxygen sensor symptoms usually come with a set of other secondary symptoms, some of which make themselves known over time. Recognizing these signs can be critical for the diagnosis.
#1. Check Engine Light.
In most scenarios, one of the initial signs of a malfunctioning O2 sensor is an active ‘check engine light‘. This happens when the check engine O2 sensor specific codes like P0130, P0141, P2270, and so on, are set in the memory of the vehicle’s PCM/ECM.
Because oxygen sensors are continuously tracked by your vehicle’s electronic components, this light functions as a preliminary alert to something misbehaving within the working limits.
#2. Reduced Engine Performance.
In some cases, one or more O2 sensors failure results in a decline in engine performance. This stem from constant shifting and from the oxygen fuel trim set to a fail-safe ‘too low’ rate. It’s because of the timid and slow biobehavior.
Being that oxygen sensors are meant to detect the volume of unconsumed oxygen in the downstream exhaust, their failure has repercussions to the ability of the PCM/ECM to determine important fueling trim data.
This divergence from the meticulously programmed fuel balance system feels like serious performance difficulties: rough idling, hesitation during acceleration, or overall sluggish engine response. Because the computer is no longer able to accurately adjust the amount of exhaust oxygen to the fuel, the engine may operate either too rich or too lean.
#3. Bad Fuel Economy.
It is not uncommon for a vehicle’s gas mileage to decline alongside the failure of an O2 sensor. This happens due to a vehicle’s engine overfuelling, in response to a missing or faulty O2 sensor and its readings.
In the absence of oxygen measurements, the engine control unit’s fuel management system typically takes a protective course of action and defaults to a rich fuel mixture, which results in unneeded combustion. Consequently, a vehicle’s fuel economy (and your wallet) suffers greatly.
#4. Changes in Exhaust Output.
You might also see your vehicle’s exhaust emissions becoming significantly darker or more heavy-set. Moreover, their odor may also be far richer than normal.
These changes happen because the oxygen sensor data that is used to regulate the exhaust system fuel ratio optimally is not working with appropriate fuel ratios. Strong fuel smell is a clear indication of unburnt fuel in the exhaust stream, while over-fueling is a sign of darker exhaust smoke.
These symptoms are most pronounced when the engine is revved up or during other activities that place the engine under load. In extreme instances, a sulfurous odor that resembles rotten eggs may be present due to the catalytic converter being affected by the fuel mixture.
#5. Failed Emissions Test.
Another telltale symptom of an oxygen sensor failure is the vehicle’s inability to pass mandatory emissions tests or inspections by the state or local government. In most cases of O2 sensor failure, tailpipe emissions are beyond the legal requirement nowadays.
The vehicle emissions control systems are unable to manage the air-fuel ratio, which results in the increased emissions of toxic gases such as carbon monoxide and hydrocarbons.
In certain states where testing is required, the failure of emissions tests can obstruct the renewal of vehicle registration and often requires a vehicle to be brought up to compliance with environmental guidelines.
Oxygen Sensor Replacement Cost
On average, having your O2 sensor replaced in your vehicle will set you back anywhere between $362 and $412. This figure includes labor expenses between $63 and $79, while parts range from $300 to $333.
This overwhelming bulk of this cost comes with labor needed to complete the replacement rather than part costs, which tend to be quite low.
This offers a great opportunity for the enthusiastic DIYer to save money since most replacement O2 sensors are available for purchase between $25 to $100.
Can I Continue Driving With a Bad Oxygen Sensor?
While a vehicle can function with a broken oxygen sensor, it shouldn’t be driven for a long time under these conditions. The O2 sensors’ feedback is used to estimate the fuel trims of an engine, and this can lead to over-fueling.
Prolonged operation of any engine fortified with an excessive fuel supply does pose some inherent risks. The first of these refers to the potential damage to the catalytic converter of a vehicle as a result of fuel contamination. This contamination relates to the overheating of the internal medium of this catalyst, which leads to its galling failure.
On the other hand, the over-fueled state of a vehicle will result in higher fuel usage, and therefore, pain at the pump. Another issue to consider is that over-fueling can make it difficult to pass emissions testing that is done on a state or municipal level.
Can an O2 Sensor Be Cleaned (Instead of Replaced)?
Cleaning a fouled O2 sensor in your vehicle is not recommended, given the remote chance of success. One of the reasons cleaning an Oxygen sensor is difficult is that the element is much more fragile than you would expect.
Replacing an oxygen sensor is much easier and straightforward than attempting to clean it. Both actions require the same amount of work; however, when replacement is conducted, the chances of success are significantly higher.
Moreover, the price when buying a replacement O2 sensor is relatively low compared to many other parts and components.
What Causes an Oxygen Sensor to Fail?
The leading cause of failure when it comes to oxygen sensors is the most common and that is, routine wear and tear.
With time, while the sensors are being used, they are subjected to continuous heat, which results in the electrical integrity being damaged. In addition to that, constant shaking should also be considered as a factort when it comes to wear and tear.
Aside from regular aging, contamination also poses the risk of premature damage to the sensors.
It is common for oxygen sensors to be exposed to unutilized fuel due to an overly rich environment in one or more engine banks, or coolant because of a head gasket failure. Both circumstances can result in premature failure of oxygen sensors.
Diagnosing a Faulty O2 Sensor
The details below might prove helpful to you in trying to manage a dubious oxygen sensor. As with any repair, you should verify specific service documentation for your vehicle before proceeding with any of the steps listed below.
#1. Check for Additional DTCs.
Using a quality scan tool, start by looking for other DTCs. There may be words from other O2-related DTCs that would be informative and point to which bank’s problem it is.
#2. Inspect the Affected O2 Sensor.
Begin the procedure with an analysis of the O2 sensor that corresponds with the fault code that was stored. If the sensor looks broken, it will need to be changed. And also, any damage to the wiring within this circuit that is discovered must be fixed before proceeding.
#3. Test Affected O2 Sensor With Multimeter.
Now, you are to check the O2 sensor with a good multimeter. It is recommended that you use a quality multimeter with the utmost care. This is best accomplished by back-probing the sensor’s signal wire with the meter’s positive lead, and the meter’s negative lead is fixed to sufficient ground.
When the engine is on and at operating temperature, the upstream O2 sensor’s readings, responding, will vary and vice versa. The downstream O2 sensors, on the other hand, level off to a setpoint somewhere in the range of millivolts.
Diagnoses that fall beyond these bounds of some standards have to be diagnosed for the purpose of O2 sensor replacement per recommended standards.