Home Diagnosis and TroubleshootingOBD Diagnostic Error Codes P0140 – O2 Sensor Circuit No Activity Detected (Meaning & Fix)

P0140 – O2 Sensor Circuit No Activity Detected (Meaning & Fix)

by Jordan Harris

Have you gotten the check engine light and a P0140 code? 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.

When you have a problem with your car, the first thing you want to do is to do research online on this specific issue. You just don’t want some sketchy mechanics to work on your car. We gearheads want to solve our own problems, even if it means needing to rent a garage to work on a car.

Especially when we are talking about sensor-related issues. Sensor-related problems are the most common in modern cars. And fortunately, this type of problem is one of these issues. These are fairly simple issues to tackle. So, if that is the case, there will be a lot to cover.

First, we are going to learn what is car diagnostics in general. Then we will cover what is bank 1 vs bank 2 and we will also learn the location of this sensor. Once we clear these topics we will cover the causes, symptoms, diagnostics process, and most importantly the price of doing all this work on your car.

Car Diagnostics

Before we dive into the P0140 code and learn more about how we can diagnose this code. Let’s first learn more about what is car diagnostics and how it is done. People are having similar issues with trouble codes and do not know how to tackle this situation. So, let’s cover this briefly and learn more about car diagnostics in general.

Being a mechanic and being a car diagnostician are two very different things. Mechanics deal with already diagnosed cars and change the things that need to be changed.

While the diagnostics job nowadays is given to the diagnostician. Even though some diagnosticians are also very capable mechanics and can do both things at the same time.


What is worth noting is that a diagnostician is basically a person with an OBD2 tool. It doesn’t matter if this is a simple scanner or more advanced software on a laptop. Plugging this laptop or scanner gives them the ability to read the trouble codes that the car shows, as well as the parameters that different sensors show.

And is able to determine what is wrong with the car. Then for a good measure, just to make sure that the component is faulty, they test the sensor with a multimeter to see if indeed this sensor is faulty or not.

So, if you want to be a successful diagnostician, you need to get two tools. An OBD2 scanner and a multimeter. And when it comes to scanners, we would recommend one that can read live data if you can afford it.

This is the case because most cheap scanners can only read the codes like the P0140. And reading live data is not possible on them. Now let’s move on and see what is bank 1 vs bank 2.

Bank 1 vs Bank 2

Another topic that we would like to cover before we elaborate on the P0140 code is the difference between bank 1 and bank 2. This is a topic that troubles a lot of car owners and wants to learn more about which bank is number 1 and which is number 2. So, let’s elaborate.

A bank of an engine is basically a line of pistons. An engine can have a minimum of one bank and a maximum of two banks.

If you have an inline engine. For example, in an inline-4, or those cars with an inline-6, you only have bank 1. So, when you get a code like this, you don’t have to learn where to look since this engine only is bank 1.

While on the other hand if you have two banks. Like in a V6, V8, V10, or V12 engine, you have to learn which of the banks is number 1 and which is bank 2.

This is the case because two banks can be confusing a little bit. And the main lead to tell which is which, is to locate cylinder number 1.

Usually, at the front of the engine, there is a stamping on the block with the number 1. But this is not always the case.

So, what you can do is find the firing order for your engine. Let’s say you have a Chevy V8 engine. You just browse the phrase “Chevy V8 firing order” or “Chevy 350 firing order” and you will get a ton of diagrams and references.

Usually, cylinder number 1 on these engines is located at the right side of the engine bay if you look at the engine from the front.

So, it is relatively easy to find. But what about the P0140 code? More about that, we will cover in a moment.

What Is An O2 Sensor

So, we learned what is bank 1 and what is bank 2. Now let’s move on and learn more about what is an O2 sensor. Knowing what an O2 sensor is, is really important when it comes to sorting out the P0140 code.

So, what is an O2 sensor? Well, the O2 sensor is also known as an oxygen sensor or lambda sensor. This is a special sensor that is installed on the exhaust manifold of the car which helps adjust the air-to-fuel ratio and also the work of the catalytic converter.

So, that’s why you have two O2 sensors. One is before the catalytic converter which helps to monitor the air-to-fuel mixture and the second sensor monitors the exhaust gases by the catalytic converter.

This is why you should not be confused by them. Even though they look the same, they are doing two different tasks. So, we can say that the first sensor before the catalytic converter is somewhat more important than the sensor after the catalytic converter that we are going to cover next and its location.

Bank 1 Sensor 2 Location

Now let’s take a look at the location of bank 1 sensor 2. Why is this so important? Well, we will learn more about that in the following chapters when we will elaborate on the P0140 code. So, where is this sensor located?

Bank 1 sensor 2 is located on your bank 1. This is the bank that has cylinder number 1. As we noted previously, on the bank there is a stamp with the number 1. Or if you cannot find this stamping, look for the firing order of your engine online and see some pictures.

So, once you cleared the location of bank 1, let’s see where sensor 2 is located. Sensor 2 is located after the catalytic converter.

So, you have sensor 1 before the catalytic converter and sensor 2 after the catalytic converter. To sum things up bank 1 sensor 2 is the second O2 sensor on the first bank. For more insight, we’ve also looked at the bank 2 sensor 1 location on a Ford F150.

Bank 1 Sensor 2 Upstream Or Downstream

Another thing that we would like to cover before we dive into the P0140 code is the topic of whether this sensor is upstream or downstream.

Upstream and downstream are also two words that confuse a lot of people. So, to simplify things, we can state that the upstream sensor is sensor 1, while the downstream sensor is sensor 2.

So, in our case, this sensor 2 that we are focused on in this article, is the downstream sensor of your car. And when you think about it, it makes sense, the first sensor sits higher and this sensor is always the upstream sensor while sensor 2 sits lower and is the downstream sensor.

For more references, do check out our guide on the bank 1 sensor 1, the bank 1 sensor 2, as well as whether bank 2 sensor 1 is upstream or downstream.

O2 Sensor Circuit No Activity Detected (B1S2)

Now let’s cover one of the oxygen sensor codes that we will be focused on from now on in the article. And this is the P0140 code. But what does this code mean? Let’s elaborate.

The definition of this code is “Code P0140 – O2 Sensor Circuit No Activity Detected (B1S2)”. So, this means that the second O2 sensor on bank 1 is causing a problem. More specifically no activity was detected as the definition states. So, what does this means?

Well, the important thing to note is that the PCM is generating 0.45V of the reference voltage to the sensor. Then after the O2 sensor reaches the operating temperature, it will start to generate voltage depending on the oxygen content in the exhaust.

A lean state will generate less than 0.45v, while a rich state will generate more than 0.45v. As you probably know, this sensor does not work like the first sensor.

Sensor 1 helps the PCM to adjust and manage the A/F ratio, while this sensor monitors the exhaust fumes by the catalytic converter and makes sure that is working at the proper level.

So, because of this, the second sensor switches from low to high voltage a bit slower than the front sensor. And in a case when the voltage is somewhere between 0.425v and 0.474 volts, if the signal stays for a long time in this certain range, this P0140 code will be triggered.

P0140 Code Causes

So, we cleared the meaning of the P0140 code, now let’s discuss more about the P0140 causes. Knowing the causes is really important for you if you want to diagnose a problem with your car.

Since there could be a few things that are wrong with the car and not only the O2 sensor. So, let’s cover these probable causes and learn more about what could trigger this code on your car.

The following might also be the causes of other O2 sensor-related OBD diagnostics trouble codes, including (but not limited to):

P0140 Code Causes #1: Silicone Or Other Compounds Poisoning

The first and one of the most common causes for the P0140 code is the poisoning that can occur to this O2 sensor.

There are some compounds that act like poison for these O2 sensors. Namely, rich air-to-fuel mixture, lead poisoning, glycol poisoning (antifreeze), and silicone (additives) poisoning.

All these conditions can affect the life of the sensor and cause it to fail. More specifically if you use additives, there are silicone compounds that basically stick to the sensor and prevent it from working well.

Also, antifreeze is a common cause of the failure of these sensors. Rich A/F mixture or oil burning can also kill them. But to a lesser extent compared to the previous ones that we mentioned. Now let’s move on to the next set of causes for this problem with the P0140 code.

P0140 Code Causes #2: Short In The HO2S

The second most common cause for the P0140 code is the short in the HO2S sensor. So, what is the HO2S? Well, the HO2S is the heater element in the O2 sensor.

Every O2 sensor has a heater element that helps the sensor reach to proper working temperature much more quickly. This is needed in order for you not to experience some of the symptoms that are associated with a bad O2 sensor.

So, if the heater element is not working, a P0140 code can be present, or possibly there could be a problem with the work of the catalytic converter in this case since this sensor monitors the catalytic converter performance. Now let’s move on to the next probable cause.

P0140 Code Causes #3: Shorted Signal Circuit In The O2 Sensor

The next cause for the P0140 code that we are going to cover is a short in the signal wire of the O2 sensor. This signal wire can also create a short and prevent the sensor from working properly.

The signal wire is basically the signal that the O2 sensor sends to the PCM (powertrain control module). So, the PCM is able to read and see more about the condition of the sensor, as well as the work of the catalytic converter.

So, you also have to test the signal wire before you decide to replace the sensor. Later on, we are going to cover how you can do this. Now let’s move on to the next probable cause for the P0140 code.

P0140 Code Causes #4: Melted Wires Or Connector

The next probable cause that we are going to cover when it comes to the P0140 code is the situation when you have melted wires and connectors.

And this could happen very often because the O2 sensor is exposed to a lot of heat from the exhaust and could easily come into contact with the hot exhaust.

In these cases, wiring can be melted and there could be a short in the system. Also, the connector can get melted as well. So, it is definitely worth checking these components out before you replace the O2 sensor.

P0140 Code Causes #5: Water Damage In The Connector

The next very common cause for the P0140 code is water damage in the connector. As you probably know, the O2 sensor plugs into a connector that is connected to the wiring harness.

And this connector could easily rust from the inside. In winter there is a huge amount of salt thrown on the streets and some of this salt can enter and spoil the connections. Checking the connector thoroughly is the way to go.

P0140 Code Causes #6: Blown Fuse

And the last cause for P0140 on our list is the blown fuse. The heater element has a 12v supply line. And this supply line is constantly running on 12v.

This is why there is always a fuse in your car, just in case something happens, the fuse blows instead of fire to go off inside your engine bay.

P0140 Code Symptoms

Now let’s cover some of the symptoms of the P0140 code. As you probably know, every malfunction always triggers some symptoms to develop. And so is the case with the P0140 code.

The most common symptom as you probably know is the check engine light on the odometer. Or malfunctioning indicator lamps in some older cars, this light is known simply as MIL.


Besides that, there shouldn’t be drivability concerns because this is the second sensor on your car. This means that this is not the sensor that adjusts the air-to-fuel ratio. But the one that makes sure that the catalytic converter functions properly.

In these situations, you might also get codes concerning the catalytic converter. Like the P0420 code or P0430 code. But besides that, you will have no major drivability issues on your car. But how you can diagnose the problem and troubleshoot the issue? Let’s further elaborate more on that in the next chapter.

Diagnosing P0140 Code

Now let’s take a look at how you can diagnose a P0140 code and solve this problem with the O2 sensor. What can you do in these cases?

Well, the first thing you want to do is to remove all the codes, and if the P0140 code sticks, this is a problem with bank 1 sensor 2.

Next, you want to do is get underneath the car and check the wires and connector. Make sure that there is no corrosion on the pins and if there is clean them well.

Also, the wires should be in tip-top shape. So, if the wires are naked, you should clean them up and insulate them properly.

You would also need to remove the sensor from the exhaust and check the condition. If the sensor is black and smells of gas, you have a rich condition that is possibly causing it to malfunction. Also, check if there are white spots. This is the case when the sensor is poisoned by coolant or silicone products.

If there is some kind of poisoning, clean the sensor and this will probably help.

And also, you want to test the sensor and the wiring from the harness to the sensor with a multimeter. More in detail on how you can test this sensor, you can check the video that we attached above.

Another good tip if you have an engine with two banks is to swap the sensors from one bank to the other. And if there is a P0160 code, it means that indeed the sensor is faulty.

Oxygen Sensor Bank 1 Sensor 2 Price

Now let’s discuss more about the price to sort out this problem with the P0140 code. How expensive is the cost to replace an O2 sensor?

Well, if you diagnosed your sensor and you have determined that there is a problem with it, what you can do is replace it. And an O2 sensor usually is between $150 and $350. They are somewhat expensive. But it will solve your problem.

Also, make sure that you get proper OEM replacement since cheap knockoffs often can be faulty from the start.

P0140: In Conclusion…

In this article, we have covered quite a bit when it comes to the P0140 code. First, we learned what is car diagnostics, bank 1 vs bank 2. As well as what is an O2 sensor and how important this component is.

After that, we discussed the P0140 code and learned the main causes of why this problem appears. Overall, the major problem is a faulty O2 sensor, lastly, we discussed how you can diagnose the problem and how much will it cost to solve it.

Frequently Asked Questions

Now let’s answer some frequently asked questions.

What Does The Oxygen Sensor Do

The oxygen sensor as its name implies is a special sensor that measures the level of oxygen inside the exhaust. This sensor helps adjust the air-to-fuel ratio, as well as keep the catalytic converter working to optimal performance.

Where Is The O2 Sensor Located

The O2 sensor is located on the exhaust. More specifically, there are two sensors on each bank. So, one sensor before the catalytic converter adjusts the A/F ratio, and the second after the catalytic converter makes sure that the catalytic converter performs as it should.

What Does Bank 1 Sensor 2 Mean

This is the location of the O2 sensor that is affected by a problem. This is the second sensor on the first bank. So, if you have an inline engine, this is the second sensor after the catalytic converter. If you have a V-engine, you have to find cylinder number 1, then the exhaust where sensor 1 is located. Usually on the right side when you open the hood.

P0140 How To Fix

Fixing this problem is simple. First, check the wiring and see if there is some damage. Also, check the connector for proper contact on the pins. Then you can do is to check the sensing element and clean the sensor. If this doesn’t help, replacing it is the only option. Another thing you can try if you have two banks is to swap the sensors, this way you will be able to tell if one of them is bad. If the sensor is bad, you will have a P0160 code.

Can You Clean An O2 Sensor

Yes, you can clean an O2 sensor, and you can spray it with a carburetor cleaner. Just spray the sensor and soak it in the carb cleaner. This will loosen up the carbon or other deposits on the sensing element and hopefully make it work again.

How To Replace O2 Sensor

Replacing an O2 sensor is simple. Just unplug the connector and then get a wrench. Unbolt the sensor from the exhaust and bolt the new sensor in. Plug in the connector and you will be good to go. Also, clear off the codes after you replace the components in order to get rid of the check engine light.

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