Oxygen Sensor Codes Keep Coming Back – Explaining the Issue

When oxygen sensor codes keep coming back, it indicates that you are not addressing the right issue. As a vehicle owner, it can be worrisome when these error codes keep coming, especially after a replacement.

Why Do My Oxygen Sensor Codes Keep Coming Back Causes and Solutions

There are several reasons for reoccurring error codes, and a faulty O2 sensor isn’t always the cause. Our automobile experts discuss all the possible causes of this problem and lists several ways you can fix them.

Why Do Your Oxygen Sensor Codes Keep Coming Back?

Your oxygen sensor codes keep coming back because of a non-defective O2 sensor, improper installation, or even leaks. An error code that wasn’t well reset and damaged wires are also common culprits. If you’re unsure which one it is, we discuss various possible causes to help with easy identification.

– The Error Code Was Not Cleared

One common reason your sensor error code keeps coming back is that it hasn’t cleared. Even after the necessary replacement, your computer may not recognize you have resolved the problem. In this case, the fault code will keep showing until you carry out a quick fix, which involves driving your car.

– Your Oxygen Sensor Wasn’t Bad

If your O2 sensor error codes keep returning after a replacement, your sensor wasn’t the problem. It’s easy to assume your sensor needs replacing because some error codes appear, including its name, but you should consult a professional mechanic before replacing any part of your vehicle.

If your oxygen sensor was never at fault, you’ll keep getting reoccurring error codes because the real problem is still unknown.

– You Replaced the Incorrect Oxygen Sensor

Replacing the incorrect O2 sensor also causes reoccurring sensor error codes. Depending on how many exhaust pipes your car has, you may have between two to six oxygen sensors. Most cars usually have two sensors known as Upstream and Downstream. The Upstream sensor keeps the engine running well through constant communication with the ECU.

The Downstream sensor compares readings with the first sensor and communicates to the ECU when there’s a problem. It ensures that the first sensor and the catalytic converter are working correctly. But a faulty downstream sensor can give false readings, causing the ECU to think the first O2 sensor is bad.

Hence, even after replacement, you may notice that the error codes keep showing. Other vehicle sensors can also compromise ECU readings and cause you to replace the wrong sensor.

– You Installed New O2 Sensors Incorrectly

Improper installations are another common reason why these error codes keep reoccurring. If the sensor isn’t installed or placed in the correct position, it won’t function as it should. In this case, the error codes will keep showing.

Aside from this, several symptoms show a wrongly-installed O2 sensor. First, your check engine light will come on, and you’ll experience engine performance issues. Your car will start to misfire, stall or make unusual noises. You may also notice that your engine consumes more fuel than normal.

– Excessive Carbon Accumulation at the Sensor’s Tip

Often, there’s a deposit of unburned fuel whenever the air fuel mixture leaves your exhaust system. If these deposits aren’t discarded often, they can lead to carbon accumulation at the sensor’s tip.

Causes of Oxygen Sensor Codes Keep Coming Back

This carbon accumulation also affects your fuel systems and air intake valves. With time, it will compromise your O2 sensor’s performance and, if left unchecked, can cause serious damage.

– Contaminated O2 Sensor

Although not so common, a contaminated O2 sensor can also cause error codes to keep appearing. An O2 sensor can become contaminated when there’s an excess fuel mixture.

Leaks in the engine head gasket can also contaminate the O2 sensor, especially when it results in burnt coolant in combustion chambers. Finally, a contaminated O2 sensor can happen when the component is exposed to too much alcohol or corrosive chemicals.

– A Newly Replaced Oxygen Sensor May Generate Error Codes

A new O2 sensor can also cause the sensor error code to keep coming back. It is likely to show if there’s little or excessive fuel mixture detected in the new O2 sensor. Likewise, fault codes can also occur when your new sensor has to burn off gas. Hence, a failing oxygen sensor isn’t always the problem; sometimes, a new O2 sensor can be the culprit.

– Bad O2 Sensor Wiring

Another cause of a reoccurring error code is when the O2 sensor has wiring issues. Sometimes, these wires can become worn, loosened, or damaged. When this happens, the sensor doesn’t get enough current to send signals to the ECU. This can cause the sensor to give off false or inaccurate readings, leading to reoccurring fault codes.

– Faulty Fuel Injectors

Having defective fuel injectors is another potential cause of reoccurring error codes. It could either be broken or clogged with dirt and carbon buildup. If this happens, there will be a reduction in the fuel supply to the engine.

Faulty Fuel Injectors

Hence, the combustion process works with a reduced fuel mixture which can cause engine-related issues, especially misfiring.

This unburned fuel from frequent misfires goes through the exhaust chamber and damages your O2 sensor. You’ll deal with reoccurring error codes if you replace the damaged sensor without first repairing your defective fuel injector.

– Faulty Mass Air Flow Sensor (MAF)

A MAF sensor measures the air coming into the engine for better combustion. This important component can become faulty due to clogging, improper installation, or even corrosive cleaning agents. A faulty MAF will cause O2 error codes to appear because it may signal a low air level in the engine.

If left unchecked, a bad MAF can damage other parts of your car, including the catalytic converter. Hence, you should carry out a thorough diagnosis of your engine so you don’t need to replace the wrong sensor.

– Vacuum Leaks

If your intake manifold has broken, it’ll lead to leaks. These leaks introduce excessive air into the intake manifold without going through the MAF that measures airflow.

The excess air will cause a misreading as both the ECU and O2 sensors will have different readings. When this happens, it triggers the check engine light, and you may get error codes with the O2 sensor name on them.

– Low Fuel Pressure

A bad fuel pump often causes low fuel pressure. Low fuel pressure will cause the air-fuel mixture to become lean, affecting the engine and the exhaust system. In this case, the O2 sensor readings will also be affected and may not tally with that of the ECU.

When you scan your vehicle with an error code scanner, you may get an O2 sensor error code. This doesn’t mean the sensor is faulty; it may signal a lean air-fuel mixture. You need to consult a professional mechanic to avoid replacing a functional O2 sensor instead of fixing your fuel pump.

– Bad Spark Plugs

Bad plugs can generate an O2 sensor error code. Bad plugs are one of the main reasons oxygen sensors go bad. They cause engine misfires, which can introduce excess air to the engine and exhaust pipe. This, in turn, affects the readings of the O2 sensor and ECU.

What To Do if Your Oxygen Sensor Codes Keep Coming Back?

If your oxygen sensor codes keep coming back, you can carry out a diagnostic test on the oxygen sensor. It also helps to know what sensor needs replacing. You may also need to fix leaks, a faulty MAF sensor, and fuel pumps.

If you’re unsure what to do, you can always visit an auto repair shop and let the professionals handle it.

– Carry Out a Diagnostic Test on the Oxygen Sensor

Before deciding you have a bad oxygen sensor, it’s advisable to test it. You can do this with an OBD2 scanner or a multimeter. First, warm up the engine so the O2 sensor can reach the right operating temperature. After that, run your engine at a high rpm while connecting your scanner to the car’s computer.

A functioning O2 sensor will display fluctuating output voltage, whereas a faulty one will have a constant output voltage or slow response. The cost of replacing a faulty oxygen sensor depends on the brand and model of the car and how many sensors need replacement. The replacement could cost between $150 to $500.

– Determine Which Oxygen Sensors You Have

If you are not sure about the number of O2 sensors you have, you may need help to figure out which is the cause of reoccurring error codes. You can consult a professional mechanic if you need help determining which sensor is at fault.

On your own, you can perform a diagnostic test with an OBD2 scanner or multimeter. This way, you can prevent replacing the wrong sensor.

– Drive the Car

You don’t need to fret if you replace your O2 sensor and it still shows reoccurring error codes. Your computer may be slow in detecting the resolution, so you need a simple fix to clear the error code. You only need to drive your car for some minutes so that your ECU registers that you have resolved the problem.

You may also need to turn off your battery for some minutes and then turn it on. Finally, you may have to reset the codes using an error code scanner.

– Carry Out a Reinstallation

If a diagnostic test by a professional mechanic indicates an improper installation, you need to carry out a reinstallation. Ensure all wires are well-aligned and connected and the sensors are well-placed.

Solution for Oxygen Sensor Codes Keep Coming Back


Place the O2 sensor 8 inches after a collector and 18 to 24 inches before the exhaust system. If you’re unsure how to do this, it is best to leave the job to a certified mechanic who can carry out proper installations.

– Clean Your Exhaust System

Carbon accumulation can also cause reoccurring error codes, so you must clean your exhaust system as often as possible. You can start by cleaning the outer pipe with soap and water. You can also clean out the inner part as far as you can go.

If that’s impossible, pour a degreaser inside and outside the exhaust pipe and let it sit for some minutes. After, use a rag or steel wool for a thorough cleaning. You may choose to add a metal polish after cleaning for a fresh, clean look.

– Check and Replace Damaged Wiring

If the wires connected to your O2 sensors are loose, worn, or broken, it is important to replace them immediately, but you should first inspect them to check which wires are faulty.

Once you sort this out, replace the wires as soon as possible. You may also want to check all screws and bolts to ensure they’re tightened well. If they appear cracked or loosened, adjust them as necessary.

– Check Internal Circuit

Although seldom discussed, you may need to check your internal circuit to ensure it isn’t the culprit. Sometimes, a reoccurring error code doesn’t mean the O2 sensor is faulty; it may have to do with the sensor’s heater circuit.

Hence, you should check your internal circuit to make sure that it is well connected or doesn’t have damaged wiring. You may also need to update your PCM, although it is quite rare for the module to cause a malfunctioning circuit.

– Repair Faulty MAF and Fuel Pump

You can fix the issue of reoccurring error codes by repairing your faulty MAF sensor. Fixing the sensor will eliminate error codes that keep coming back. It will also reduce engine performance issues like misfiring, jerking, stalling, and lean idling.

Likewise, you should fix a bad or defective fuel pump to improve fuel pressure. A functional fuel pump supplies the right air-fuel mixture, which enables the O2 sensor to take proper readings.

– Seal Leaks

Fixing leaks in the intake manifold is another way to resolve reoccurring engine code problems. Check the rubber tubes in your intake manifold for signs of cracks or damage. If you notice any, replace them immediately.

Repairing leaks is inexpensive, so you should be able to do this immediately. Also, check that your engine head gasket isn’t leaking. If it is, it would be best if you repaired it soon enough to avoid a drop in coolant temperature.

Frequently Asked Questions

– Why Does Check Engine Light Remain on Despite Replacing O2 Sensor?

Your check engine light remains on despite replacing your O2 sensor because you replaced the wrong sensor. Other common reasons include damaged wires, faulty MAF, defective catalytic converters, and even bad fuel injectors. These can cause your check engine light to remain on even though you’ve replaced the O2 sensor.

What about repeated failure of the O2 sensors? Repeated O2 sensor failure can come from contaminated oxygen, improper installation, damaged wiring, and a faulty MAF. Leaks in the intake manifold or a defective fuel injector and pump can also cause it.

– How Long Does Check Engine Light Stay On After O2 Sensor Replacement?

The check engine light may stay on for hours and even days after replacing an O2 sensor. You may need to take several drives to fix this. You may also need to switch the engine battery on and off to reset the error code and turn off the warning light.An error code scanner can also reset the code and turn off the warning light.

– Will the Car Turn Off if There Is an O2 Sensor Error Code?

Yes, the car can turn off if there is an O2 sensor error code, especially when you’re idling. A compromised air-fuel mixture, especially one that’s lean if left unchecked, will cause your engine to shut down and turn off when you’re idling.

Why Do My Oxygen Sensor Codes Keep Coming Back Conclusion


A reoccurring O2 sensor error code doesn’t mean your sensor is faulty.

Here’s a quick summary of what we’ve discussed in this article:

  • Why do your oxygen sensor codes keep coming back? The error codes can reoccur if there’s an issue with your MAF, fuel injector, and fuel pump. Improper installation or replacing the wrong sensor can also cause error codes to keep coming back.
  • You can fix this problem by finding out which sensors you have before replacement. Also, carry out a diagnostic test before replacing any car part. Check and fix damaged wirings, internal circuits, defective fuel injectors, and intake manifold leaks.
  • If you cannot determine the specific problem, make sure you contact a professional mechanic.

We hope this guide makes it easier for you to identify why the error codes are reoccurring and fix them soon.

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