Bad Oxygen Sensor Symptoms, Causes, and Replacement Cost

Your vehicle contains different to monitor the performance of different parts. An oxygen sensor or O2 sensor is one of the major vehicle sensors. It is used to measure the oxygen level in the exhaust gases and send this data to the vehicle powertrain control module (PCM). When the oxygen sensor goes bad, it produces different signs. This article explains the bad O2 sensor symptoms, causes, and its replacement cost.

Symptoms Of a Bad Oxygen Sensor

When an oxygen sensor or O2 sensor goes bad, it produces different symptoms, such as rough idle, stalling engine, poor fuel economy, unusual noise, poor engine performance, catalytic converter failure, and black smoke from the exhaust, along with an illuminated check engine light. Your vehicle may also fail emission tests.

The following are the most common symptoms of a bad O2 sensor:

1) Check Engine Light Illuminates

check engine light, symptoms of bad oxygen sensor

An illuminated check engine light is one of the first symptoms of a faulty O2 sensor. In some cases, this may be the only noticeable issue, without any other evident signs of a faulty sensor. When the oxygen sensor goes bad, the check engine light may illuminate along with a specific trouble code.

A faulty oxygen sensor may also trigger an error code, such as P0172, P0161, P0130, P0131, P0140, P0132, P0133, P0137, P0134, P0141, P0031, or P0030. These codes usually indicate an issue with the air/fuel mixture, which can be attributed to the O2 sensor.

2) Stalling Engine

Vehicle Stalling

In some cases, a rough idle can escalate to the point where the engine stalls. Initially, this issue may manifest as a misfire and typically occurs when the issue with the oxygen sensor or other components remains unsolved.

If your vehicle engine fails to maintain the necessary power to continue operating, it may turn off. While it is usually possible to restart the engine, there is no guarantee, as it depends on the specific circumstances and the severity of the problem.

Read More: Engine Stalling Causes and Prevention

3) Rough Idle

Rough Idle

One of the potential symptoms of a faulty oxygen sensor is experiencing rough or unstable idling while your vehicle is parked or stopped. Typically, a car’s idle speed should be about 1,000 RPM or lower. If the RPM suddenly increases, it can be indicative of a problem with the oxygen sensor.

But it’s important to note that a rough idle can also be caused by other components responsible for maintaining the air/fuel ratio in the engine. Therefore, it is necessary to consider this symptom in conjunction with other potential symptoms.

4) Poor Fuel Economy

Poor fuel economy, symptoms of bad O2 sensor

The poor fuel economy is one of the primary symptoms of a bad oxygen sensor. Your vehicle’s engine requires a precise amount of air-fuel mixture to ensure the proper combustion process.

When the O2 sensor goes bad, it starts sending wrong information to the vehicle’s PCM. When the PCM receives wrong information, it may force the fuel injection system to send more fuel than required.

As a result, the engine may burn more fuel, leading to a decrease in fuel efficiency. When your engine starts to consume more fuel than usual, you need to stop the vehicle and fix the issue.

5) Poor Engine Performance

Poor Engine Performance

Poor engine performance is one of the clear signs of a bad oxygen sensor. When the normal combustion process in the engine is disturbed, it may result in noticeable issues with engine performance. The engine will generate less than usual.

You can easily observe this symptom, particularly when attempting to accelerate. Initially, these performance problems may be subtle and go unnoticed.

However, if left unresolved, these issues can worsen over time, eventually making driving more challenging. Therefore, it is crucial to address any detected faults promptly, especially to prevent potential accidents on the road caused by the lack of acceleration. A decrease in engine performance serves as a strong indication that a faulty oxygen sensor may be at fault.

6) Unusual Noise

The unusual noise coming from the engine is one of the clear signs of a faulty O2 sensor. When your oxygen sensor doesn’t work effectively, it may cause the accumulation of too much carbon within the combustion chamber. This can lead to an issue called a lean-running mixture.

When the air-fuel mixture becomes lean, it may lead to pre-ignition issues. The pre-ignition of the air-fuel mixture may cause a noise called knocking or pinging.

But it’s important to note that these unusual sounds may also be produced due to some other causes, including engine damage, low-quality fuel, a faulty spark plug, a bad ignition coil, or a blocked fuel injector.

7) Failed Emissions Test

Failed Emission Test

As we discussed above, the O2 sensor of your vehicle is one of the most important parts of the emission system. It helps to control the emissions of exhaust gases. When it goes bad, it can lead to higher emissions of exhaust gases. The excessive emissions of exhaust gases may lead to failed emission tests.

However, there can be various other reasons for the emission test to fail, but a faulty oxygen sensor is one of the main issues. If your vehicle’s emission test is not passed, it is recommended to scan the vehicle’s main computer by using a scanner. Through this process, you may find the underlying issues.

8) Catalytic Converter Failure

Bad Catalytic Converter due to bad O2 sensor

Continuing to run the vehicle with a faulty oxygen sensor can eventually lead to the failure of the catalytic converter. An imbalanced air-fuel mixture caused by a faulty O2 sensor can have bad effects on the catalytic converter.

Therefore, it is crucial to ensure the O2 sensors are in optimal working condition to prevent your catalytic converter from damage.

Read More: Bad Catalytic Converter Symptoms and Causes

9) Black Smoke from Exhaust

Black Smoke from the Exhaust Pipe

When the oxygen sensor of your vehicle becomes faulty, it disrupts the air-fuel mixture within your vehicle’s engine. This poor mixture leads to poor combustion, causing issues such as backfiring, unburned fuel, or the emission of black smoke from the tailpipe.

Additionally, you may experience poor idling, high fuel consumption, and difficulties in starting the engine.

10) Rotten Egg Smell

Rotten Eggs Smell due to a faulty oxygen sensor

When the O2 sensor becomes faulty, it may cause a supply of excessive fuel to the engine cylinder. The excessive supply of fuel to the engine may lead to a smell resembling rotten eggs, which is caused by the presence of sulfur.

Causes of Bad O2 Sensor

The oxygen sensor becomes faulty due to one or more of the following causes:

1) Accumulated Carbon Deposits

Accumulation of carbon due to a rich air-fuel mixture is a common problem that can lead to oxygen sensor failure. Several factors can contribute to this, such as a faulty fuel injector or a clogged air filter that leaks or is not functioning properly.

2) Coolant Leaks

The coolant leakage in the combustion chamber can cause significant damage to oxygen sensors. This can occur when there are issues like a leaky intake manifold gasket, a leaking cylinder head gasket, or a cracked cylinder head.

3) Dirty Fuel

The usage of dirty fuel may badly affect the performance of the O2 sensor. While this situation is rare, it is essential to be aware of the potential impact of dirty fuel on sensor performance.

4) Wrong Fuel

Using a fuel octane rating that is lower or different from the recommended level can be harmful to sensors and their functioning.

5) Ignorance

Neglecting early signs of malfunctioning oxygen sensors can result in further deterioration and complications.

6) Normal Wear and Tear

Over time, your oxygen sensor may wear out as other mechanical parts. When it is worn, its performance compromises.

What is the function of an O2 Sensor?

The O2 sensor or oxygen sensor is one of the most important parts of your vehicle’s exhaust system. The main function of the oxygen sensor is to measure the level of unburned O2 in the exhaust system. It sends this information to the powertrain control module (PCM) of your car. The PCM utilizes the data of the O2 sensor to determine the optimal air-fuel ratio for optimal engine performance.

O2 Sensor

The O2 sensors of your vehicle play a major role in the exhaust system. When the vehicle’s PCM detects an excess of oxygen, it makes necessary adjustments and sends commands to other sensors to increase the amount of fuel and vice versa. Without this adjustment, your engine may experience issues due to running either too rich or too lean.  

Since 1981, oxygen sensors have been mandated for all vehicles, and different vehicle models manufactured after 1996 are equipped with multiple O2 sensors. These additional sensors are utilized to measure the performance of the catalytic converter.

Oxygen Sensor Location

The oxygen sensor is typically located in the exhaust system, either on the exhaust manifold or near the engine. In some vehicle models, multiple oxygen sensors are installed, all serving the purpose of measuring the oxygen levels in the exhaust gases.

Oxygen Sensor Location

In the case of multiple oxygen sensors, another sensor can be found after the catalytic converter. Its role is to monitor the converter’s efficiency by comparing the readings obtained before and after the catalytic converter. This comparison helps assess the performance of the converter.

How to Test an O2 Sensor

Follow the below-given symptoms to test a bad oxygen sensor:

  • First of all, connect a scanner to the vehicle and turn on the engine.
  • Allow the engine to run at a fast idle (around 2,500 RPM) for approximately 2 minutes to ensure the oxygen sensors reach their normal working temperature and adjust accordingly.
  • Verify that your car is operating in closed-loop mode by monitoring the activity displayed on the scanner.
  • Enable the “snapshot” mode on the scanner.
  • Maintain a steady engine speed during the process and start recording the data of the O2 sensors using the snapshot mode.
  • After recording, check the captured snapshot frames. Place a marker next to the voltage range of each O2 sensor.
  • Analyze the results deeply. The main purpose of this analysis is to get a comprehensive overview, particularly focusing on two voltage ranges: 0 to 300mV and 600 to 1,000mV. If the maximum readings fall in the middle range, it is likely an indication of a malfunctioning upstream oxygen sensor.

Oxygen Sensor Replacement Cost

The replacement cost of the O2 sensor depends on different factors such as your vehicle model, labor cost, and the type of brand. The average replacement cost of the oxygen sensor is from $40 to $460.

The labor cost highly influences the replacement of the oxygen sensor. If you have the necessary tools and knowledge, opting to replace the sensor yourself can save you from paying a mechanic. The oxygen sensor itself costs from $20 to $170, taking the DIY approach can result in significant cost savings. It is recommended to consult your vehicle’s manual for guidance during the replacement process.

Oxygen Sensor$20 to $170
Labor Cost$20 to $290
Total Cost$40 to $460

FAQ Section

What happens if you don’t replace the oxygen sensor?

Failure to replace the oxygen sensor can prevent your vehicle’s main computer from gauging the air-fuel ratio accurately. This inaccuracy can cause your engine to run either overly rich or too lean. This imbalance may lead to different issues, such as poor engine performance, failed emission tests, rough idle, misfiring, or poor fuel efficiency. Over time, it may also induce heavy wear and tear on the engine, potentially damaging costly components such as the catalytic converter or integral engine parts.

What are the codes of bad O2 sensors?

When the O2 sensor becomes faulty, it triggers a trouble code such as P0172, P0161, P0130, P0131, P0140, P0132, P0133, P0137, P0134, P0141, P0031, or P0030.

Can I replace the oxygen sensor myself?

Yes, in most scenarios, changing an O2 sensor is a relatively straightforward task. Nonetheless, the simplicity of the job depends on your vehicle’s make and model. For older vehicles, rust might cause the oxygen sensor to seize, making its removal challenging without the use of specialized tools.

Can I drive with a bad oxygen sensor?

Yes, you can drive, but it’s generally not recommended to drive with a defective oxygen sensor. A bad O2 sensor may lead to a lean air-fuel mixture, resulting in excessive emissions and poor fuel efficiency. In certain instances, a faulty oxygen sensor may also activate the check engine light.

Can I clean my Oxygen Sensor?

Yes, you can clean your oxygen sensor but isn’t always required. If your sensor is mildly dirty, your vehicle’s PCM might still be capable of regulating the air-fuel mixture effectively. But if your sensor is clogged badly, you should replace it.

Can a bad O2 sensor cause poor acceleration?

Yes, a bad O2 sensor may lead to poor acceleration. However, initial damage from a faulty sensor might appear minimal; the harm will worsen over time with continued use. Ultimately, you might encounter issues like a lit-up check engine light, rough idling, engine misfires, sluggish acceleration, and failure in emission tests.

How long does an Oxygen Sensor last?

The service life of an O2 sensor depends on vehicle maintenance, fuel, engine oil, and driving habits. Typically, an oxygen sensor can last for 30,000 to 50,000 miles, though some may have long service life. If you notice your poor fuel efficiency or poor engine performance, it could be a sign of a faulty O2 sensor.

Can a bad O2 sensor cause the car to shut off?

Yes, a faulty oxygen sensor can cause the car to shut off. This sensor plays a vital role in regulating the air supply to the engine. When it goes bad, it may stop the oxygen sensor supply to the engine. When your engine doesn’t receive sufficient oxygen, it may shut off.

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