Home » 6 Reasons Oxygen Sensor Codes Keep Coming Back

6 Reasons Oxygen Sensor Codes Keep Coming Back

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If you’ve ever had a vehicle’s check engine light come on, you know how frustrating it can be. You take your car to the mechanic and get it fixed, but it still comes back. You drive your car around for a week, but it still comes back. This problem is common, especially in newer cars that have a lot of sensors to track engine performance.

So why does this happen? Why do oxygen sensor codes keep coming back?

Oxygen sensors track air/fuel ratio or exhaust emissions to keep your car running at its best. The problem is that these sensors use tiny electrical wires that can break or wear out over time. Such damage can inevitably affect your car’s performance and increase maintenance costs.

Understanding O2 Sensor Codes

Understanding O2 Sensor Codes

The oxygen sensor is an integral part of your vehicle’s exhaust system. Its core role is to signal the powertrain control module (PCM) of any abnormal levels of oxygen. It detects oxygen levels via heated wire sensitive to the air/fuel mixture. The PCM receives these signals and adjusts fuel delivery to the appropriate levels, keeping emissions down and engine efficiency up.

In plain English, an oxygen sensor monitors the amount of oxygen in your car’s exhaust to keep your engine running properly. Typically, this sensor is located close to the exhaust manifold or after the catalytic convertor.

When there are issues with your car’s oxygen levels, you may see error codes P0420 or P0150 among others. These codes indicate that your exhaust system is faulty or has leaks or if there’s a malfunction in your oxygen sensor.

How Does the Vehicle Communicate Faulty Sensors?

How Does the Vehicle Communicate Faulty Sensors

As the name suggests, the powertrain control module is what governs data drawn from the vehicle’s sensors. It also collects feedback from the camshaft position sensor and the O2 sensor.

If your car has been running fine but then begins to misfire and run poorly, it could be due to a faulty oxygen sensor. A bad oxygen sensor can also cause rough idling, poor acceleration, and a loss of power.

For instance, if you have a P0420 code, you may have replaced your oxygen sensor incorrectly, or you might have ruined them. That’s where the PCM comes into play.

When the PCM gets a sign that one of these sensors is faulty, it sets a fault code and records it in its memory.

Moreover, engine or emission problems indicate malfunction of faulty wiring or engine control module (ECM). These problems may prevent proper communication between sensors and computers.

6 Reasons Oxygen Sensor Codes Keep Coming Back

6 Reasons Oxygen Sensor Codes Keep Coming Back

1.    You installed new O2 sensors incorrectly

Incorrect sensor placement means it won’t communicate well with one another. There may also be communication problems with your engine control module (ECM).

To install oxygen sensors well, place them on top of each other, so they form a triangle shape between them. Next, tighten all bolts/screws with a torque wrench.

2.    You exchanged the wrong O2 sensor

Most modern cars have two O2  sensors. When you have a problem with your vehicle, it’s easy to get confused about which sensor is faulty. Therefore, replacing a sensor that wasn’t the faulty one can be one of the most common reasons oxygen sensor codes keep coming back.

If you’re not sure which sensor is faulty or just not sure where to start, diagnose your engine; then check if you need to replace both.

3.    Your oxygen sensor was not faulty at first

If you replaced an oxygen sensor before and have this error code, come back again, it may be because you replaced the wrong component.

It’s also possible that your original oxygen sensor wasn’t faulty.

Maybe other engine problems are responsible for the false readings from the sensor.

4.    The fault code did not reset after replacement.

It’s easy to forget that the code didn’t reset after replacement. So, when your check engine light comes back on again, it might seem like the new sensor is bad. If this is the case, your car may need more time to pass the test again after replacing the O2 sensor.

5.    Replacing an oxygen sensor may cause a new code

Other times, replacing an oxygen sensor causes a new code to display on your vehicle’s OBD-II system. This display happens due to the latest alert on “how much fuel your car is using” vs. “how much gas the new sensor should burn off.

6.    Excessive carbon buildup on the tip of the sensor

Buildup happens when your exhaust stream has excess unburned fuel. Too much-unburned petroleum can cause incomplete combustion inside the engine cylinder head.

As unburned fuel exits the exhaust valve into the manifold, it leaves behind deposits. This soot may build upon each tip of an O2 sensor over time, causing one or more sensors to fail!

Ask your mechanic to remove any deposits before placing new oxygen sensors to avoid a repeat.

FAQs About Why Oxygen Sensor Codes Keep Coming Back

FAQs About Why Oxygen Sensor Codes Keep Coming Back

1.    What Can Cause a False O2 Sensor Code?

A false oxygen sensor code results from an error in your oxygen sensor’s monitoring system.

This false alert can happen for many reasons, including:

  • The wiring for your oxygen sensors is faulty or corroded.
  • Your oxygen sensors are malfunctioning or broken.
  • Your engine computer is not functioning well.

If you notice the code, check if the wiring is okay. If there’s no damage to any wires and everything seems in order, take your car for a diagnostic test to be sure.

2.    After Changing the Oxygen Sensors Why Is My Check Engine Light Still On?

There may still be an issue with your oxygen sensors.

It’s also possible that the light is on due to another issue like:

  • a bad catalytic converter
  • electrical issues
  • a misfiring cylinder

When you have this problem, the first thing to do is to ensure your battery has enough power. Also, replace any bad batteries that might be causing electrical issues in your car.

After that, you can take your car in for a diagnostic test to see if you need to change any other sensors.

3.    Why Does My Oxygen Sensor Keep Failing?

There are many reasons why an oxygen sensor may fail repeatedly. One of the most common is the contamination from carbon deposits.

Other reasons why oxygen sensor codes keep coming back include:

  • Faulty wiring or poor electrical connections
  • Exhaust leaks near the sensor
  • Vacuum leaks in the fuel system (which may cause inaccurate readings)

Worn parts –e.g., exhaust manifold– also affect engine airflow, causing failing sensors.

4.    How Many Miles Do You Have to Drive to Reset Oxygen Sensor?

The short answer is to reset the oxygen sensor after driving at least 100 miles.

It’s a common belief that you can reset your oxygen sensor by driving a certain number of miles. But this doesn’t work for everyone. This inconsistency is because different cars reset their sensors at different millages.

With that said, resetting the oxygen sensors depends on things like:

  • the age of the vehicle
  • the kind of air filter installed
  • the period after replacing the exhaust system

If your car doesn’t pass emissions tests, then it’s likely that you’ll need to replace the sensor(s) rather than reset it. Nevertheless, there’s no harm in trying the reset procedure first. But if it doesn’t work and emissions problems persist, replace the sensor instead.

Final Words on Reasons Oxygen Sensor Codes Keep Coming Back

If you want to save money on diagnostic trouble codes in general (not just oxygen sensor codes), try using a code reader with a generic OBD II code guide.

It will tell you which of the many possible malfunction causes is most likely. If it isn’t apparent, keep plugging away until you understand what’s wrong so you can address the underlying cause rather than put a temporary band-aid on it.

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