10 Bad O2 Sensor Symptoms (Causes and Solutions)

Do you want to know the various bad O2 sensor symptoms so as to know when the O2 sensor is going bad? If so, you are on the right page.

The O2 sensors convey air-fuel measurements, which enter into your car’s engine, to the ECU/PCM to regulate it accordingly. The O2 accounts for the altitude, barometric pressure, and engine/ambient temperature, to discern if the engine burns a rich or lean mixture.

Whenever the sensor becomes faulty, it would not engage the correct level of fuel injection, ensure sufficient combustion of fuel or regulate exhaust gas.

The car might release carbon-based compounds or harmful environmental pollutants as time goes on, leading to poor engine performance. Detecting a faulty oxygen sensor on time is necessary because the O2 sensors play a vital role in the emission and performance of your vehicle. A bad gas mileage, intermittent stalling, or a never-ending check engine light are some indications you need to check for.

Let’s discuss the bad O2 sensor symptoms you should look out for and how to fix them.

1. Frequently Failed Emission Tests

The oxygen sensor is simply an emission equipment manufactured to lessen air pollutants emitted by controlling the air-fuel mixture of your vehicle from a tailpipe.

The oxygen sensor is important for passing through emission testing, which is a general necessity for the complete registration of a vehicle in the non-USA area.

Some states don’t need these tests. However, it’s common for some drivers not to go through this point at all. When you fail the emission test continuously, it might show that either all or one of your oxygen sensors is bad.

2. Illuminated or Flashing Check Engine Light

One of the reasons the Check engine light goes off is because of a bad oxygen sensor. Though many people are unaware, it’s a subtle cause, which means that the oxygen sensor can not activate the check engine light alone but can influence the system of the vehicle to fail and result in putting on the CLE. Since the check engine light could mean that an engine component is malfunctioning.

So it would be better to use an OBD2 Diagnostic scanner to procure error codes that will show you the exact component or system that is faulty.

Examples of these codes that are normally seen in nowadays models of vehicles are P0131 (oxygen sensor circuit low voltage), P0162 ( system too rich), and P0136 (Heated O2 sensor circuit malfunction). Otherwise, the accurate diagnosis would compel you to contact a local mechanic.

3. Rough Idling, Misfiring, or Stalling

If your oxygen sensor is not faulty, it will not throw off the oxygen fuel ratio in your vehicle since it controls the combustion interval and timing of your engine needed for active combustion.

If you observe any irregularities in the engine, like rough idling or frequent misfiring along the lines, you can say you are having symptoms of a bad oxygen sensor.

Other issues that can come from a failed O2 sensor are stalling, power loss, and engine hesitation whenever you want to start your car. Another sign is when your car feels slow unnecessarily. Out of the 3 symptoms stated, the one anyone could notice on time is the rough idling, followed by misfiring and then stalling.

Your vehicle will still come on if it’s the first two symptoms, but if it’s stalling, it could be that the issue of misfiring has been neglected for long, to the extent that your engine cannot sustain itself anymore with the working piston remaining in the cylinder block of your vehicle.

At this point, it will be difficult to determine if the bad oxygen sensors indirectly or directly cause the problem. To know exactly what the problem is, first replace the spark plugs. But if you observe that it could be fuel starvation that leads to the starting and stalling problems, control it by conducting a fuel pressure test.

This helps discern whether the issue is with the fuel pressure injectors, regulator, or other components. Then you can go ahead with replacing the faulty oxygen sensor if you’ve checked these components.

4. Poor Fuel Economy

Consumption of fuel over time increases slowly, most especially for carbureted, older vehicles, and it’s normally caused by engine components that are worn out. But if it emerges after you have installed a new O2 sensor or abnormally, it’s either the air-fuel mixture is running rich or lean.

Usually, the next thing to do is solve the problem by rectifying your car’s carburetor settings or changing the loose vacuum hose. A severe drop in fuel economy is part of the symptom of a bad oxygen sensor and calls for replacement, vehicles with Denso Oxygen sensors are included.

5. Bad Engine Performance

Difficulty in combustion caused by a discrepancy in air-fuel ratio and faulty oxygen sensor leads to poor engine performance. Generally, the drop in performance is caused by stalling, misfiring, or intermittent idling.

Bad oxygen sensor symptoms will sometimes vanish as you start moving your vehicle. Regardless, don’t be relieved yet. If this is not attended to on time, it could escalate or be accompanied to speed stasis, sputtering, engine hesitation or restricted acceleration, and loss of power or power surges. This shows that you must visit a mechanic before going on a trip.

6. Engine Noises

Since a bad O2 sensor fails to operate as an emission equipment, the vehicle might have unnecessary carbon deposits inside the combustion compartment because there is no air-fuel mixture control. Consecutively, this leads to a lean mixture that causes engine pinging/knocking sounds and, among other things, pre-ignition.

This symptom is very controversial and, most times, doesn’t mean a faulty O2 sensor immediately. Usually, it points to the need for top-end work or a dirty carburetor. Nevertheless, It would be worth it if you check the conditions of your sensor, especially if it makes a sound when idle.

7. Black Exhaust Fumes

The fuel and air quantity in your engine will become uneven if you have a bad oxygen sensor because the device that regulates the fuel and air intake release is not functioning properly.

Eventually, this affects the combustion efficiency, resulting in backfiring, soot-like smoke emitted from your vehicle’s exhaust, backfiring alongside hard starting problems, and high fuel consumption.

8. Sulfuric/Rotten-Egg Smell From the Exhaust

A sulfuric or heavy gasoline smell from the tailpipe goes with the black smoke residue, which are symptoms of a bad oxygen sensor. But there might be some cases whereby they indicate an issue with your vehicle’s fuel injector or system.

Whichever way, the smells indicate a surplus of fuel in the engine, and you have to correct the air-fuel mixture of your vehicle. To be safer, perform troubleshooting steps to address the O2 sensor problem and the fuel system. This will help you to pinpoint what exactly caused the Smell.

9. Sudden Catalytic Converter Failure

The catalytic converter is a component of the emission system, similar to the oxygen sensors. It operates by alternating between the lean and rich mixture and controls the quantity of air inside the exhaust.

Therefore, lessening the toxic gases delivered into the atmosphere. Though it consists of the main components of the emissions system, it still relies on oxygen sensors to operate properly.

Naturally, the catalytic converter would experience damage to the extent that it’ll fail if the oxygen sensors start to malfunction and deliver an incorrect reading to the PCM.

You would know if all or one of the catalytic converters is failing if you experience these symptoms:

1. Oil burning as a result of worn-out cylinders, rings, seals, or valve guides
2. Misfiring of ignition due to shorted plug wire or fouled spark plug
3. Internal leakage of coolant as a result of cracks in the head gasket
4. Fuel contamination
5. Physical or corrosion damage
6. Compression misfiring due to leaky head gasket or valves

10. Engine Overheating

Continuous overheating of the engine is not a common symptom of a faulty oxygen sensor. It’s mostly associated with issues related to the electrical system or top end of the vehicle. But it’s rare for it to relate to oxygen sensor problems.

Overheating means that the owner of the vehicle ignored the early signs of a bad oxygen sensor to the extent that the sensors are severely worn out, and the replacement is overdue.

Even with the risk of damage, overheating causes some drivers to push the limits of their oxygen sensors. And this symptom would stay until the bad sensor is replaced.

Also Read: How to Remove O2 Sensor without Socket (Step by Step)

Reasons for Premature Oxygen Sensor Failure

1. Components such as the carbon build-up from the engine, dirt, grime, or debris might get into the fuel system and air intake, which could lead to damaged oxygen sensors.
2. Failure to inspect your vehicle at least once a year
3. Ignoring early symptoms of damaged oxygen sensor without addressing it
4. Due to lack of maintenance, the oxygen sensors might become gunked or caked.
5. Not following the recommended replacement schedule of the O2 sensors
6. Using a lower or incorrect fuel octane rating than what is recommended
7. Making use of fuel additives for a long time could influence the exhaust fumes and the air-to-fuel mixture of the vehicles
8. Skipping on periodic changes or scheduled maintenance of air and fuel filters and spark plugs could damage oxygen sensors and cause combustion inefficiency.
9. Fuel contaminants, low fuel quality, or excessive fuel burning in the engine can clog the oxygen sensors and, in turn, seize to accurately measure the release of fuel.
10. Physical damage from the oxygen sensors area can be seen along with the catalytic converter, exhaust manifold, or exhaust system.

O2 Sensor Replacement Cost

Immediately you notice any of the symptoms discussed, don’t wait for a long time before replacing the oxygen sensor. It should be replaced immediately.

Or else, you might be putting the engine to risk. Then the cost of repair will now be expensive. Since replacing the O2 sensor is affordable and simple, you should not have any excuse for not doing it.

An average cost for replacing an O2 sensor is about $60-$300. This depends on the model and the make of the vehicle. The cost of the parts can be between $20-$200, while the cost of labor is between $40-$100. It depends on if you are changing either or one of the oxygen sensors and the location you go to.

For an average economy vehicle, you just have to pay the estimated price of about $250. This isn’t a big investment in keeping the exhaust system and the engine running in good condition and protecting it.

Also Read: 6 Fuel Pressure Sensor Symptoms (+ Solutions)

When Should I Replace the O2 Sensor?

Whenever you observe any of the signs, you might be unsure if replacing the O2 sensors is necessary. But like every other vehicle component, the O2 sensors can get damaged. And replacing it would ensure your vehicle’s safety and fuel efficiency.

If the manufacturing date is like 15 years back, replacing the O2 sensor is vital for every 60,000-90,000 miles. A deteriorating and old O2 sensor might not send correct feedback.

Following up on the maintenance schedule would help you avoid toxic emissions and failures. Immediately you notice a symptom like blinking of the check engine light or weak gas mileage, visit your mechanic for inspection.

How Long Do O2 Sensors Last?

There are a lot of answers to this question online. The oxygen sensors can last for about 30,000 & 100,000 miles. And the durability of the oxygen sensors is based on if your vehicle is old or new.

Vehicles manufactured in the last fifteen years have their oxygen sensors last for about 3 to 5 years or 30,000-50,000 miles before replacement is needed. On the other hand, vehicles nowadays have oxygen sensors that last up to 7 to 10 years or 60,000-100,000 miles.

Is It Risky to Drive your vehicle With a Faulty O2 Sensor?

It is unreasonable to drive your car despite knowing that the oxygen sensor is bad. Apart from the fact that you are releasing fumes harmful to the environment, you are running the car to encounter engine damage, which could be prevented if the faulty oxygen sensor were replaced immediately.

Delaying is not going to help you save your money. Most importantly, you’re putting yourself at risk on the road by driving a car with a bad sensor that cannot monitor the fuel delivery and air intake.

Also Read: P0430 – Meaning, Causes, Symptoms & Fixes

Frequently Asked Questions – Bad O2 Sensor Symptoms

Conclusion – Bad O2 Sensor Symptoms

Whenever you encounter any symptoms that have been discussed, it’s more likely that the oxygen sensor is damaged and needs replacement.

To start the replacement process, you can do some things, including checking the warranty status of your vehicle and gathering vital tools. The replacement steps are simple and can be done within 1 hour.