Can a Bad O2 Sensor Cause Misfire? Causes & Fixes

Since the engine’s performance depends on the oxygen sensor, it is essential to understand why. Several variables, such as the length of combustion cycles and the air-to-fuel ratio, directly impact the data read from an oxygen sensor.

If the o2 sensor is not working correctly, it will send incorrect data to the ECU( Engine Control Unit). Based on the inaccurate data, the ECU will adjust the fuel injectors incorrectly, causing the engine to misfire occasionally or all the time.

What Are the Symptoms of a Bad O2 Sensor?

A cheap preventative measure that can help avoid more expensive problems is the replacement of an oxygen sensor. In this manner, the computer in your car will be able to adjust the ratio of fuel and air in the engine as necessary.

bad oxygen sensor

Numerous variables, such as the outside temperature, altitude, barometric pressure, engine temperature, and engine load, impact how much oxygen is present in an engine. The mixture is said to be rich when an excess of fuel is left over after combustion. More nitrogen oxide is released into the atmosphere when a lean mixture is used.

The following are warning signs that your oxygen sensor may be faulty.

Flashing Check engine light

If the oxygen sensor in your car is malfunctioning, the Check Engine light on your dashboard will illuminate a bright orange. A Check Engine light could indicate a severe issue with your engine, but it could also be caused by something as simple as a loose gas cap. A professional mechanic should inspect your car to determine the source of the problem.

Poor MPG

Due to worn-out engine components, fuel consumption increases over time in older, carbureted vehicles. As a result, the air-fuel ratio in your car is probably either too rich or too lean if it occurs frequently or soon after you’ve installed new oxygen sensors.

Common next steps in resolving this issue include adjusting the car’s carburetor settings or tightening a loose vacuum hose. However, this sharp decline in fuel economy indicates a faulty downstream O2 sensor in fuel-injected, computer-controlled vehicles. 

Black smoke

Your engine won’t function properly if your O2 sensors are faulty, as the mechanisms that control air intake and fuel delivery won’t be functional. This results in unburnt fuel, backfiring, or soot-like smoke from the exhaust, high fuel consumption, poor idling, and hard starting issues

Rotten egg smell for exhaust

Strong gasoline or sulfuric odors from the tailpipe and a residue of black smoke are signs that an O2 sensor is malfunctioning. They might also point to a fuel or injector issue with the vehicle. Whatever the reason, this odd smell is a sign that the engine’s air-fuel ratio needs to be adjusted because there is too much fuel in the system. Therefore, it is advised to carry out troubleshooting procedures that address fuel system and oxygen sensor issues to be safe. 

Increased emissions

A faulty oxygen sensor is a leading cause of failing emissions tests. If you wait too long to replace a defective sensor, it could cost you thousands of dollars to get your car back in working order. As a result, the car might start to smell like rotten eggs. In addition to putting you and your family at risk of carbon monoxide poisoning, a faulty oxygen sensor could put you in danger.

Rough idling

A properly functioning oxygen sensor prevents the oxygen-fuel ratio from ever becoming unbalanced by regulating the timing of the engine and the combustion intervals required for efficient combustion. Bad downstream O2 sensor symptoms include frequent misfiring, rough idling, and similar engine irregularities. Another sign is if your car feels slow for no apparent reason.

The rough idling of a car is one of the first signs of a faulty O2 sensor that a driver will notice. A misfire usually accompanies it, and then the vehicle will stall out. The first two will allow you to keep driving even if your car isn’t performing as well as it could be. When an engine stalls, it is usually because misfiring has been ignored for too long or has gotten so bad that the engine can’t keep running on the few remaining good pistons in the cylinder block.

Poor engine performance

A poor air-fuel ratio and faulty O2 sensors are the root causes of poor combustion, leading to a lackluster engine. Misfiring, idling, or stalling symptoms usually come before a performance drop. You shouldn’t be reassured if the signs of an O2 sensor failure disappear once you get going. If not fixed right away, it can lead to sputtering, a loss of speed, difficulty starting the engine, a lurching sensation, a halt in acceleration, a hesitating response, a surge in power, or even a complete shutdown. So, to sum up, don’t put off going to the mechanic.

What Happens If I Unplug My O2 Sensor? 

Bad gas mileage, diminished performance, and a failed emission test are all possible outcomes if you disconnect your o2 sensor. In addition, your car’s O2 sensor may reduce the fuel injected for combustion if you’ve installed performance parts like exhaust headers and nitrous.

This is due to your O2 sensor detecting high pollution levels and taking measures to lower that pollution, which causes a drop in performance. For this reason, some auto racing fans choose to forgo using O2 sensors in their vehicles.

For a better understanding on how an O2 sensor works, check out the video below:

Can I Run My Car Without an O2 Sensor? Will It Damage the Vehicle?

If you want to boost your car’s performance, you probably want to remove the oxygen sensor. After installing performance parts like exhaust headers and nitrous, the O2 sensor can detect too much pollution and leftover fuel. The engine control unit (ECU) may respond to these signals by injecting less fuel, limiting performance improvement.

The O2 sensor is also responsible for activating the vehicle’s “check engine” warning system. That’s fine and dandy for the show’s duration. However, O2 sensors are built in to ensure that the average passenger enjoys a productive, economical, and emission-free journey.

If you disconnect the oxygen sensor, your engine control unit (ECU) won’t be able to determine the optimal fuel injection rate. The electronic control unit will revert to its factory settings, maintaining a constant fuel injection rate. As a result, performance may suffer, or fuel economy may plummet.

Will a Bad O2 Sensor Throw an Error Code?

It has been discovered that a faulty oxygen sensor is not the root cause of most problems that trigger sensor codes. A mechanic will need to do more than just read a trouble code (like 61-1, p1604, p1133, or others) that indicates an issue with the oxygen sensor. As a result, blindly screwing in a new sensor because a sensor-related code has been detected is risky.

The best mechanics will only use the error codes as a jumping-off point for further investigation. Someone who has done their homework will likely request a diagnosis.

The oxygen sensors in a car allow the computer that regulates the fuel injection to make instantaneous, pinpoint adjustments to the fuel supply. Cars have at least two and probably four sensors unless it is older than 20 years. Before the catalytic converter, there is another sensor.

This sensor allows the engine computer to adjust fuel delivery for optimal combustion, output, and emissions control. One more sensor is installed after the catalytic converter in the exhaust system. This sensor checks to see if the catalytic converter is doing its job and keeping the exhaust system clean.

Due to their limited scope, oxygen sensor fault codes (such as p0420, p0141, and p0135) do not always indicate a need for replacement. Instead, another system component may be at fault, making the oxygen sensors appear inaccurate. Indeed, this is the case with the vast majority of engine error codes

Will Replacing the O2 Sensor Stop the Misfiring?

Replacing the oxygen sensor will stop the misfiring only if a faulty o2 sensor causes the root problem. If there is something else causing the misfire, replacing the sensor won’t fix the problem. By running the car with disconnected sensors, you can test whether the o2 sensor was the fault. If the engine stops misfiring, your issue is a faulty oxygen sensor.

In Summary

A misfiring engine can have multiple causes, hence diagnosing the issue correctly can be a little tricky. If you do not have the right tools and knowledge, it is better to have a professional mechanic do the diagnosis. However, it is important to find the right man for the job; hence I recommend checking Google maps for reviews on your local repair shops.