P0155 – O2 Sensor Heater Circuit Bank 2 Sensor 1 (How To Fix)

Have you experienced the check engine light and the code P0155? Well, if that is the case, then you are at the right place because, in this article, there will be quite a lot to cover on this topic.

Having the check engine light on is a situation that nobody really likes. When you have a check engine light, you just know that something is wrong, and the more you ignore it, the problem will become greater and greater This is why proper diagnostics is essential when it comes to tackling this issue on your car.

And by this, we mean that you should diagnose your car first. Especially if you are into DIY stuff and you want to wrench on your vehicle. Since that’s what we gearheads do, we work on our cars and solve our problems by ourselves and not let anybody else mess up with our cars.

Then we will cover the O2 sensor and see where bank 2 sensor 1 is located. After that, we will elaborate on the P0155 code meaning and see what is the definition of this code. Once we clear that out of our way, we will cover the causes, symptoms, and how to diagnose the problem. So, if you want to learn more, follow along.

Car Diagnostics

Now that we cleared the basics out of our way and learned more about what we will cover in this article, let’s first take a look at car diagnostics and how this process is done to a car. Not everybody here is an expert, so we feel the need to further elaborate on this process and how it is performed.

If you owned a classic car or your parents owned one, you are probably quite familiar that there is nothing too complicated going on inside of these cars. And honestly, cars back then were a real breeze to repair. You were able to tell immediately what is wrong after hearing how the engine worked or simply by driving the car on the road.

Nowadays cars are extremely loaded with technology. This technology made them a lot more reliable since there are dozens of sensors and also a computer that regulates everything. But still, there are some things that can often fail and cause a major headache to car owners.

And when these sensors fail or get some bad readings, they will notify you with the check engine light. And the only way to learn why this check engine light is there is to diagnose this car with an OBD2 scanner tool. You plug this tool into the OBD2 port and let it scan for codes.

Then if you get a P0155 code, you move on to troubleshoot the problem. So, in this case, the problem is caused by one of the O2 sensors. In this situation, you need to have a multimeter to see what indeed is causing the problem since not all the time, the problem is found in the sensor but in something else.

Bank 1 vs Bank 2

The next thing that we would like to discuss before we dive into the code P0155 is the bank 1 vs bank 2. This would be really useful to know and we are going to see later why is this the case. So, what is bank 1, and what is bank 2?

Bank 1 and bank 2 simply refer to the engine block. For example, an inline engine only has one block. So, all inline engines, no matter if they are inline-3, inline-4, or cars with an inline-6, they have only 1 bank.


When it comes to V6 or V8 engine layout, it is worth noting that in this case, you have two banks. And this is bank 1 and bank 2. So, how you can tell which is which? Which side is bank 1 and which is bank 2?

Well, the only way that you can tell is to locate cylinder number 1. Usually, cylinder number 1 is located on the right side of the engine bay. Also, there will be a stamping with the letter 1 on the cylinder block where this cylinder is located.

You can also do online research and look for your engine and see the firing order of the cylinders and then compare. There is a lot of visual information out there as well. Just type the name of the engine + “firing order” and you will get a lot of information. It is really simple. Now let’s move to the next topic before we cover the P0155 code.

O2 Sensor

Now let’s take a look at what is an O2 sensor before we cover the P0155 code. What does an O2 sensor do in reality?

An O2 sensor is also known as an oxygen sensor or lambda sensor. This sensor simply measures the oxygen content inside the exhaust.

So, the oxygen sensor is mounted on the exhaust manifold. What is important to note about this sensor is that the sensor monitors the oxygen flow and then adjusts the air-to-fuel ratio of your car, ensuring that you always get the best and most optimal air-fuel ratio.

That’s why we can frankly say that this is a very crucial component. Each car has at least two of these sensors. One is upstream and one is downstream. The upstream comes before the catalytic converter and the downstream comes after the catalytic converter.

In the next chapter, we going to learn the location of the sensor that we are interested in this article.

Bank 2 Sensor 1 Location

Another interesting topic that we would like to cover is the bank 2 sensor 1 location. Where is this sensor located on your engine?

Well, this sensor is only installed on V6, V8, V10, and V12 engines. So, there has to be a bank 2 where this sensor is mounted.

Usually, if you look at the car from the front, bank 2 is located on the left side. This is where cylinder two is located. But for the exact location, we mentioned that you should dive deeper and look at some diagrams online and learn the location of cylinder number 2 for your specific engine.

So, if you found bank 2, next you will need is to look for the exhaust manifold. And sensor 1 should be located on this manifold. While sensor 2 that we are not interested in for this article is located after the catalytic converter.

For more insight, you can check out our guide on the bank 2 sensor 1 location in a Ford F150. In addition, we’ve previously discussed whether bank 2 sensor 1 is upstream or downstream, as well as where you can find bank 1 sensor 2, in addition to bank 1 sensor 1.

But what is the P0155 code meaning? More about that, we are going to elaborate next.

O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)

Now let’s take a look at the P0155 and learn more about what this code means. What is the definition of this code? Let’s elaborate.

The simple definition for this code is “P0155 O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)”. But what does all this means?

Well, this means that the sensor that we discussed previously, more specifically the Bank 2 Sensor 1 has a problem inside it or something else is causing it to malfunction.

More specifically when it comes to the malfunction is that the heater element inside of the O2 sensor doesn’t work.

If you didn’t know, O2 sensors have heating elements inside. So, when you do a cold start, the heater element will turn on, so the sensor gets up to temperature much faster.

And when this component breaks, it doesn’t mean that the whole sensor is faulty, only the heater element. But this P0155 code can be caused by other culprits as well. And more on that, we will learn more in the following chapters.

P0155 Causes

So, we have covered the P0155 code meaning and learned what is the meaning of this code. We learned that there is an issue with the heater element of bank 2 sensor 1.

But not let’s further elaborate on the problem and learn more about all the possible scenarios for this situation. Since there could be more than a bad sensor in this issue.

P0155 Causes #1: Bad Upstream Oxygen Sensor Heater Element

The first on our list of causes for the P0155 code is the bad heater element in the O2 sensor located on bank 2 sensor 1 position.

As we noted previously, these sensors have heater elements inside that make sure that the sensor is up to temperature after you give the engine a cold start.

This is needed since the temperatures in the exhaust do not immediately climb up. This is why every O2 sensor needs a heater element. And unfortunately, this heater element can fail. And when it fails, you are stuck with a P0155 code or a similar one.

But how to diagnose it? More on that in a bit, now let’s move on to the next cause.

P0155 Causes #2: Bad Connector

The second common cause for the P0155 code is a bad connector. As you probably know, these O2 sensors are really exposed to the elements.

So, there could be salt, water, heat, and other contaminants that could damage the connector. The connector could melt, or inside the connector, the pins can rust out.

And when this happens, there is no longer a proper connection between the sensor and the wiring harness of the car. So, it is very useful to check the connector before you jump to conclusions and replace the O2 sensor on your car.

Nowadays these sensors have three or four wires, which makes them more prone to issues like these with the code P0155. Now let’s move on to the next possibility.

P0155 Causes #3: Short Or Open Ground

The next probable cause for the P0155 code is a short on the wires for the heater element.

On 4-wire sensors, there are two wires that are intended for the heater element. So, what can happen is that these wires can get damaged or melted and cause a short and stop the heater element from working. In this situation, you will get the P0155 code.

Also, there can be a situation when you have an open-ground connection. This means that the sensor is not properly grounded and can malfunction in a similar manner to this.

As you can tell, wires are exposed to a lot of heat since they are very close to the manifold and can melt and then short out. So, it is definitely a good idea to check them out before deeming the sensor guilty of the problem.

P0155 Causes #4: Blown Fuse

The next possible cause for the P0155 code that we are going to cover is the blown fuse. If you didn’t know, this sensor is regulated with fuses since it has a heating element.

There are two fuses that you should check in case they have popped. Ford more specific information, you should see some diagrams specific to your model.

You can also pop off the fuse box cover and on the inside of the cover there should be a map for each fuse what it is and what it does. Then after you inspect the fuses carefully, you can change the ones that have failed.

But take note that when a fuse fails, there is a reason behind it. Fuses pop off for security. And this means that inside the sensor heater element or the wiring, there is a problem. So, if you replace the fuse and everything is good, then you are good to go.

But if there is an issue, there is highly likely something wrong and this problem with the P0155 code can repeat in the future.

P0155 Causes #5: Coolant Temperature Sensor Not Working

The next possibility and probable cause for the P0155 code is a bad coolant temperature sensor. So, what is a coolant temperature sensor?

Well, this is a sensor that measures the temperatures of the coolant inside the engine. This sensor is really important, it activates the fans, and also helps adjust the air-to-fuel mixture.

So, when you do a cold start in the morning, this sensor will send a cold signal to the PCM. And this will indicate that more fuel has to be injected into the cylinders.

And if this sensor has a bad reading, this could also affect the O2 sensor heater element. The computer will think that the car is warmed up, so the heater element will not activate. Which can confuse the computer even more and trigger codes such as these.

So, if you have a coolant temperature sensor code, such as a P0118 code, along with the P0155 code, make sure that you check the coolant sensor first before you jump to conclusions.

P0155 Causes #6: Bad PCM

And the last probable cause for the P0155 code that we are going to cover in this article, is the bad PCM. So, what is a PCM?

PCM stands for Powertrain Control Module. This component is also known as ECM (Engine Control Module), or ECU (Engine Control Unit).

And what can happen is that this component can fail and cause you a problem like this one in our case. It happens rarely. But it definitely can trigger a code like this P0155.

P0155 Symptoms

Now let’s take a look at the symptoms that are often present when you have a P0155 code. What are the common symptoms associated with a bad O2 sensor?

Well, the first on our list of symptoms is definitely the check engine light. Since if there wasn’t a check engine light and a P0155 code, you wouldn’t have been here. But what is good about this symptom is that you can also get other codes that are closely related to the problem.

For example the codes concerning the coolant temperature sensors or other issues with the work of the engine. Besides the check engine light, you can also expect the engine to run really rough and often stall if the problem is too serious.


But since the heater element is bad, you can expect the problems to be most serious at startup. Until the engine warms up, things can be problematic and the work of the engine not be perfectly smooth.

But after the engine warms up (check out our write-up on do you have to warm up your car to learn more), things will smoothen up and you will be able to drive the car normally since the sensing element of the sensor is not broken in this case.

Also, the gas odor can be present once you start the engine, and the car will run really rich. But as we said, things should smoothen up after a while. But how you can test this sensor and deem it as the cause for the P0155 code? Let’s elaborate more about that next.

How To Diagnose A Bad O2 Sensor

1. Now let’s learn more about how to diagnose a P0155 code. In the first video that we attach, you can see a guy that has a problem with his F-550, he replace the O2 sensor but the problem was still present. So, what he did was find out that he had a short in the wiring. So, make sure that you do these checks before replacing the sensor.

2. Now let’s take a look at how you can diagnose a 3-wire sensor with a multimeter and see if this is the root of the problem. In the video, you can see how a 3-wire sensor is tested at 6:30 min. You just need to place one probe on the first connector and the second on the third connector.

Then see how many ohms you get. The ohm rating really depends on the ambient temperature. A good sensor should produce between 4 and 4.5 ohms.

You can also test the continuity and see if you have continuity on your sensor. Place the multimeter to measure continuity. Continuity basically means that there is a connection. First test terminals 1 and 2, and then test terminals 2 and 3. If the multimeter is not beeping, then the sensor is good. If it beeps it is bad.

3. Now let’s take a look at how to test a 4-wire sensor. It is not much different compared to the 3-wire but you still have one more wire that can confuse some people, so that’s why we added this guide as well.

Cost To Replace O2 Sensor

We learned how to test an O2 sensor and see if this component is causing the P0155 code, now let’s see the cost to replace the O2 sensor. How much can you expect to pay?

Only for the part, you can expect to pay anywhere between $150 and $350. The labor will also cost you between $100 and $300.

P0155: In Conclusion…

In this article, we have covered quite a bit when it comes to the P0155 code. First, we learned what is an O2 sensor and where bank 2 sensor 1 is located.

Then we learned more about the causes, symptoms, and diagnostic process that is done to this sensor. And frankly, it is really easy to do, Just follow the instructions that we attached and you will be good to go.

Also, if you’re curious, we’ve covered the O2 sensor and faults concerning it many times before. That includes some of these OBD diagnostics error codes for the O2 sensor down below if you’re seeing something else other than P0155:

Frequently Asked Questions

Now let’s answer some frequently asked questions.

What Does The Oxygen Sensor Do

The O2 sensor is a simple sensor that measures the level of oxygen inside the exhaust. This sensor together with the MAF sensor is crucial when it comes to adjusting the air-to-fuel mixture in your car and making the car work properly.

What Sensors Can Cause A Car Not To Start

The sensors that can make the car not able to start very often are the camshaft position sensor and the crankshaft position sensor. There is only one crankshaft sensor and can be up to four camshaft sensors. Also, the MAF sensor and O2 sensors are pretty important when it comes to the ability of the car to run well.

What Does Bank 2 Sensor 1 Mean

Bank 2 refers to the bank of your engine. Only V-engines and H-engines can have two banks. This is the bank where cylinder number 2 is located. Usually, this bank is on the left side when you look at the car from the front. And sensor 1 is the O2 sensor on the exhaust manifold. Sensor 2 is after the catalytic converter.

What Side Is Bank 2 Sensor 1

Bank 2 is located on the left side when you look at your engine from the front. And sensor 1 means that this is the first O2 sensor mounted on the exhaust manifold.

Where Is Heated Oxygen Sensor Located

The heated oxygen sensor is mounted on the exhaust. There are two sensors. One before the catalytic converter and the second after the catalytic converter.

How To Test O2 Sensor Heater

You can easily test for continuity. Just tweak the multimeter to measure continuity. First, place one probe on the first pin and the second probe on the second pin. Then test pin two and pin 3, the multimeter shouldn’t beep, if it beeps the sensor is bad.

Approved Tools

These tools have been tried and tested by our team, they are ideal for fixing your car at home.

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