Home Diagnosis and TroubleshootingOBD Diagnostic Error Codes P0031 – Is Your O2 Sensor’s Heater Control Circuit Broken?

P0031 – Is Your O2 Sensor’s Heater Control Circuit Broken?

by Jordan Harris

Have you gotten the check engine light and you diagnosed the P0031 code? Well, if that is the case, then you are at the right place because there will be a lot to cover on this topic where we will cover everything you need to know when it comes to tackling this issue.

Having a problem like this can be a rather frustrating thing to deal with. Why I’m saying this? Well, because it is true. It could greatly impair the driving characteristics of your vehicle and consequently affect the performance of the car.

The car will simply stop working well and you will have a ton of symptoms that will be present when the engine starts working. So, be rather prepared for this when you are dealing with a P0031 code. But you should not worry because we are going to elaborate on the problem and also try to elaborate everything in detail so you sort the issue as soon as possible.

First, we will focus more on the basics of car diagnostics and understand more about the P0031 code. Then we will focus on the prime causes of this type of code and then we will cover the symptoms that will be present when you will be having this problem. After that, we will move on to diagnosing and fixing the issue. So, let’s get into the problem.

P0031 Code

Now before we dive into the problem with the P0031 code, let’s first introduce ourselves to the basics of car diagnostics. I bet that there are a ton of people who are reading this and are not familiar with the basic stuff when it comes to diagnostics. So, this chapter is for them.

What is important for you to understand as a beginner is that nowadays cars are packed with electronics. It is not like back in the day when the diagnostics of an engine were based on how the engine works and the only thing that you could do were some tweaks on the carburetor, some valve adjustment, and call it a day. In these modern times, things are far more complex.

Everything is connected to the PCM which stands for Powertrain Control Module. This module basically controls everything when it comes to the powertrain. It constantly tests the sensors and gets proper feedback from them to adjust the engine work.

When these tests fail, there will be problems. More notably problems with the check engine light. This is the case because this computer will notify you when there is a problem with some of these components through this check engine light.

Unfortunately, there is no such way to understand the meaning of this check engine light without getting an OBD2 scanner and performing proper diagnostics on the car.

This tool is one of the essentials that you will need to have when you are dealing with the P0031 code. Also, the multimeter is also essential because this tool will allow you to bench test these components and find out more if they are broken or not. Now let’s discuss the main component for our article which is the O2 sensor.

What Is The O2 Sensor?

Now before we start elaborating more on the problem with the P0031 code, let’s first learn more about the basics and understand how the O2 sensor works. This is probably the most important thing to know before we start understanding more about the problem. So, what is this sensor all about?

Well, this is a special sensor that is mounted on the exhaust of your car. In fact, there are not only one but two of these sensors on all cars. Some even have four of them such as the V6 and V8 engines because there are two exhaust manifolds.

So, on one exhaust manifold, you have two O2 sensors. One before the catalytic converter and one after the catalytic converter. But what is the role of these sensors?

Well, the role of these sensors is to measure the oxygen levels inside the exhaust of your car before and after the catalytic converter. Meaning that there are two checks.

Then based on this data, the PCM will be able to adjust the air to fuel ratio accordingly. So, you understand how important is the O2 sensor when it comes to this stuff. Along with the MAF sensor, they are the most important for maintaining proper work of the engine.

Another thing that you should know is that there are heater circuits installed inside of this sensor. These heater elements are basically printed into the ceramic part of the sensor and there is a special wire that goes into these components to power them up.

The power is applied to this heater element at the startup so the engine could go into a closed-loop much sooner and perform better. And here comes the problem with the P0031 that we are going to elaborate next.

P0031 HO2S Heater Control Circuit Low (Bank 1 Sensor 1)

Now as we covered the basics of the O2 sensor, we can move on and start understanding more about the P0031 code and what it means. So, what is the definition of this code?

The definition of this code is “P0031 HO2S Heater Control Circuit Low (Bank 1 Sensor 1)”. So what does this means? Well, this means that you have a fault in the O2 sensor.

More specifically, you are having a problem with the electric circuit of the heating element in the O2 sensor. This heating element is in charge of maintaining the proper temperature of the sensor when the engine starts.

So, whenever there is a circuit low, there is probably a low voltage in the circuit or a short in the circuit of this heating element on the O2 sensor. This means that the problem needs to be diagnosed and troubleshot. But for which sensor we are talking about since there are 2 to 4 sensors per vehicle.

Well, in this case, we are discussing the first sensor on the first bank of the engine. This is the sensor that is located at the bank where cylinder 1 is located. And it is the first sensor, which means that it comes before the catalytic converter. Sensor 2 is the one that comes after the catalytic converter.

And how serious is this problem? Well, it is not as serious as a complete failure of the O2 sensor. When you have a bad HO2S heater control circuit, you can drive with this car. The sensor will keep working as it should but you could face some symptoms. More on the symptoms of the P0031 Toyota, we are going to cover in the following chapters. First, let’s cover the causes of this problem.

Causes For The P0031 Code

Now as we learned the basics of car diagnostics and the role of the O2 sensor in your car as well as the problem with the P0031 code.

Now is the time to focus more on the causes of this problem. What could get wrong and cause this P0031 error code? Let’s elaborate in the following chapters.

1. Damaged Electrical Circuit Of The Heater Element In The O2 Sensor

The first and most common problem that could cause this P0031 code is a problem with the electrical circuit of the heating element.

As you probably know, the O2 sensor is exposed to millions of heat cycles and the heating element that is inside could start to degrade and the electrical wiring to short out when it comes in contact with another wire or something similar.

This is a clear example that you are having a bad electrical circuit and you need to replace this sensor. Fixing it will be almost impossible because the heating element is embedded in the body of the sensor.

There are basically two designs. The first one is a layer that is pressed into the sensor or the second type on which the HO2S is printed on the ceramic part of the HO2S sensor. So, the heater is basically in the center of the sensor, and disassembling this sensor will be almost impossible.

The only way around this will be to replace the whole component with a new one and call it a day. This will definitely fix the P0031 code. Now let’s move on to the second cause.

2. Bad Heating Element

The second probable cause for the P0031 code that we would like to discuss is a bad heating element.

As we already told you, there is the heating element and the electrical circuit that powers up this heating element.

So, when the heating element fails, it will throw you a code like in our case with the P0031 or a similar code that will tell you that the heater element is broken.

What is also bad in this case is that is the same deal. The heater element and its circuit are embedded into this sensor and removing them will practically be impossible.

You can try to clean the sensor off and hope for the best. But this will be highly unlikely that will pass. In the end, you will highly likely be needing a completely new sensor if you decide to fix the problem with the P0031 code. Unless this code is caused by something else. And that’s what we are going to cover in the following chapter.

3. Problem With The Wiring

The third most common cause for this P0031 code is a problem with the wiring. As you probably know, there are a couple of wires that go to this O2 sensor. And that is the wire for the heater element, the sensor as well as a ground connection.

These wires can also malfunction and cause a ton of troubles down the way. So, whenever you diagnose a problem like this, you need also to inspect the wiring if the heating element of this sensor results in a good performance.

Maybe some of the wires have shorted and this is causing your problem. Or possibly there is a problem with another thing such as the connector. This connector is exposed to a ton of heat that is created when the car drives. And after a lot of years of use and driving through water, it could result in rust development on the wires and frequent malfunctions.

This will then result in a P0031 code and this is a clear sign that you have an issue with the wiring. So, check the wiring and make sure that it performs well. Now let’s move to the last probable cause.

4. Faulty PCM

The last probable cause for the P0031 code that we are going to cover is a problem with the faulty PCM. As we already learned, the PCM is the component that regulates everything. In other words, the brain of the car.

Whenever there is something wrong the PCM is picking it up and reporting it to you. So, if you are having a problem with the O2 sensor the PCM will tell you that you have a P0031 code or any code depending on the root of the problem.

But what happens sometimes is that this PCM starts to fail. And when the PCM fails, it will start to report more and more problems. Your cluster will be lit up like a Christmas tree. There will be a ton of error codes concerning different components and you will think that your car will fall apart.

But sometimes this is only caused because of a bad computer. So, the computer is always a last resort option to check when you try to diagnose this problem with the P0031 Dodge.

Symptoms Of The P0031 Code

Now let’s cover the symptoms of the P0031 code. Let’s learn what type of symptoms you will be facing when you have a code like this.

As we all know, every problem is represented through a symptom and every problem has a cause. We have covered the causes, now let’s jump into the symptoms.

1. Check Engine Light

The first probable symptom for the P0031 code as you probably know since you are here is the problem with the check engine light.

Whenever the circuit of the heater is malfunctioning this will be represented through the P0031 code. This code is really descriptive and helps you a lot when it comes to solving the problem, you just know that you need to look at bank 1 where cylinder 1 is located and the sensor 1 is one that is faulty.


This sensor is the first sensor that comes before the catalytic converter. If the sensor after the catalytic converter is bad then you will get the P0032 code.

If the sensors on the other bank are bad you will get a P0051 or P0052 code.

2. Rough Engine Work At Start Up

The second very common symptom when this problem with the P0031 code happens on your car is that you will get a problem with rough engine work.

The engine will work rough when you start up the car. So, why will this be the case? Well, this will be the case because the heater element in the sensor is not heating up the sensor. This means that the sensor will only heat up when the engine starts working at optimal working temperature.

This type of work will result in very rough idle at startup as well as misfires and other things that are common in these situations. So, when you have the check engine light and the code P0031, this is a really expected situation.

3. Decrease In Fuel Economy

Another expected situation or symptom as you would call it concerning the code P0031 Toyota is the problem with the decrease in fuel efficiency.

The car will simply stop being efficient as it did in the past. This will be attributed to the rough engine work when the engine starts. This rough engine work will result in an increase in fuel demand from the PCM to be delivered into the system.


So, if you have a P0031 code and the fuel economy has dropped, then this might be the root cause for this problem on your car. This is a clear sign that you need to diagnose the problem and measure the O2 sensor heater resistance specification which is in the range of 10 to 25 ohms.

But more in-depth we are going to cover this in the following chapter where we will learn how you can diagnose this problem with the P0031 Toyota code on your car. So, follow along.

How To Diagnose & Fix P0031

Now it is time to get to business and start diagnosing the problem with the P0031 Subaru code. So, what you can do in this case and diagnose this issue?

Well, first check the car for codes and delete the codes. If the P0031 sticks and doesn’t go away then you know where to look after it. And that is the O2 sensor 1 on bank 1.

In order to bench test this sensor, you will have to remove the sensor from the vehicle and then test the heater element of this sensor first. And if the test is good then you will have to check the wiring.

First, you will have to test the sensor for resistance and you need to know the right O2 sensor heater resistance specification which is between 10 to 25 Ohms. So, you will need to get a multimeter and set it up to measure ohms.

Then measure the resistance between the two of the terminals on the connector that are in charge of the heater element. A good result should be between 10 to 25 ohms as we mentioned. If this is the case then you are having a good sensor. If it’s too low then there is indeed a problem with the electrical circuit inside of this sensor.

Then you will have to replace this sensor with a new one. Something that is necessary to sort out the problem. If the sensor is good on the other hand, then you will have to test the wiring and see if you get a good signal from it. Repairing the wiring will hopefully fix the P0031 code.

Cost To Fix The P0031

So, what will be the cost to fix this problem with the P0031 code? Well, this really depends on the problem itself. The base diagnostics process is about $120.


Then you will have to pay for the repair. A new O2 sensor is between $200 and $300 on average plus the labor involved can reach up to $450 to $500 for the whole job. Still, if you don’t face a ton of issues and symptoms, you will be good since the sensor is still working, only the heater element is faulty.


In this article, we have covered quite a bit when it comes to the P0031 code. We learned the basics of car diagnostics and the basis of the O2 sensor. Then we have covered the problem with the code and covered the causes and symptoms concerning this issue.

After that, we moved on to diagnosing and solving the problem. Overall, it is not that expensive to fix this issue since the repair can be delayed as much as you can until you get enough cash to replace the O2 sensor.


Now let’s answer some frequently asked questions.

What Does Code P0031 Mean

This code means that you have a problem with the heater element on one of your sensors. More precisely the first sensor on the first bank of your engine. This sensor is located in front of the catalytic converter.

How To Fix Code P0031

Fixing this code will require either replacing the O2 sensor which in most cases is the case. Or possibly if the wiring is faulty to repair it and hopefully work. But in 99% of the cases, the sensor is the one that it is faulty and needs replacing.

How To Test O2 Sensors With Multimeter

You can test the O2 sensor by tweaking the multimeter to DC voltage. Then you can connect the multimeter to the heater power wires with alligator clamps. Then start the engine and observe the readings. It should read somewhere between 12 to 14 volts.

What Does HTR Mean On A Code Reader

The HTR is a special symbol. This symbol is referring to the heated oxygen sensor readiness. So, if you have this symbol flashing it means that the readiness of the O2 sensor cannot be achieved due to a misfire and the P0306 code.

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