Where Is The Bank 2 Sensor 1 Located? Full Guide

Are you trying to fix your vehicle’s Bank 2 Sensor 1 fault the DIY way, but you have no idea what or where that is? Or maybe you’ve already bought the oxygen sensors to replace after an engine check error, but you don’t know what side is Bank 2 Sensor 1 on your vehicle’s engine?

Whatever the error code for a faulty oxygen sensor you get after running the car diagnostic scanner on your vehicle, the tricky part is figuring out which one of the oxygen sensors to replace. This problem comes because of not knowing how to identify or locate the reported oxygen sensors.

In this blog, we will discuss the engine error with B1 or B2, and S1 or S2 in the code displayed on the diagnostic scanner. We will specifically, discuss the Bank 2 Sensor 1 error. On other diagnostic scanners, the error is displayed as B2S1. Let’s start by getting familiar with what these terms mean.

What is a Bank in Engines?

In engines, a bank is basically a side of an engine. It is the structure that contains the cylinder heads for fuel combustion and generation of engine power. An engine bank of cylinders runs parallel to the engine’s crankshaft.

Car engines come with different types of cylinder banks. Some engines have a single cylinder bank, others have multiple cylinder banks. If the diagnostics scanner is displaying the Bank 2 Sensor 1 code, then your car has multiple cylinder banks, because clearly the error is associated with the second bank of cylinders.

Close up photo of a 4-cylinder car engine.

Most cars have V-type engines that consist of two-cylinder banks, usually with an equal number of cylinders on each bank. These banks are conveniently named Bank 1 and Bank 2. The cylinders on each bank are named by their position number on the bank. Let’s look at what makes up each of these banks.

What Makes The Bank 1 Of An Engine?

Bank 1 of the engine is always located on the side of the engine with cylinder number 1. It is the side with the most forward cylinder on the engine. The cylinders on Bank 1 are named in odd numbers.

For example, if your car has a V8 engine, it means the engine has 8 cylinders with 4 on each bank of the engine. That means the cylinder numbers Bank 1 of a V8 engine are cylinder number 1, cylinder number 3, cylinder number 5, and cylinder number 7.

This configuration is different in V6 engines, where Bank 1 has cylinders named in odd numbers. So always make sure to check with the car’s service manual.

What Makes The Bank 2 Of An Engine?

The Bank 2 of an engine is located on the side where cylinder number 2 is. Most engines have the Bank 2 cylinder offset slightly backward to make the engine run quieter and produce more horsepower due to lower friction during combustion. The cylinders on the Bank 2 are named in even numbers.

For the V8 engine in our example, the cylinder numbers on Bank 2 are cylinder number 2, cylinder number 4, cylinder number 6, and cylinder number 8. For V6 engines, the cylinders on Bank 1 are named in odd number numbers.

How to Locate Bank 1 and Bank 2

Knowing which side of the engine is Bank 1 or Bank 2 can be complicated for many people. The engine has a cylinder head cover and sometimes they are not labeled to indicate the bank types and cylinder number.

However, they are ways to know which side of your engine is Bank 1 and which one is Bank 2, and we are going to discuss them next.

Identifying cylinder numbers

The best way to tell the engine bank sides is by identifying the cylinder numbers. For most cars, other than those running a V6 engine, Bank 1 is always where cylinder number 1 is.

You can also tell the side by checking any cylinder number, and odd numbers will always be on Bank 1.

Locate by hand side

You can also tell which side the engine banks are by what side of the engine they are located. To do this, you will have to stand behind the engine, and look toward the front of the engine. The bank on your left-hand side will be Bank 1, and the bank on your right-hand side will be Bank 2.

Standing behind the engine to tell the hand side does not necessarily mean standing behind the car. Engines are mounted differently. You have to open the hood first to see the mounting type of the engine.

If the engine is mounted sideways, also known as transverse mounting, where the timing belt or chain is not facing the front, the back of the engine will be the side away from the timing belt.

For inline-mounted engines, where the timing belt is facing the front of the car, the back of the engine faces toward the back of the car.

By driver or passenger side

You can also tell the side of the bank in inline-mounted engines by the location of the driver’s and passenger’s seats. This is not possible in transversely-mounted engines, as the sides of the seats indicate the back or front of the engine.

In most V-type engines, Bank 1 side is located on the side of the passenger’s seat. Bank 2 is located on the driver’s seat side.

Check for the offset in the alignment of cylinders

The surest way to know which side is Bank 1 or Bank 2 on your engine is to see which one of the sides is closer to the front of the engine. As discussed before, the front of the engine is the side with the timing belt connected.

Bank 1 will always be the closest to the front, and Bank 2 is slightly offset toward the back. This is because of the offset design of the cylinders in V-type engines.

What is a Sensor in Engines?

Sensors in engines is the name given to the oxygen sensors in computer-controlled car systems. They are important components in the car’s ability to regulate the ratios in the air-fuel mixture during combustion in the cylinders.

They are connected to the exhaust system of the vehicle to sense how much oxygen is in the exhaust fumes and report back to the computer system in real time. The computer will then use this input to regulate the amount of gas released by the fuel injectors for combustion. This is called a closed-loop system.

There are two types of sensors, according to how they are used and their location in the system. Every oxygen sensor falls into one of these categories. These are Sensor 1 and Sensor 2.

What is Sensor 1 of an Engine?

Sensor 1 of an engine is the oxygen sensor located in the exhaust manifold flanges, and before the catalytic converter. It is also known as an upstream sensor. It helps to calculate and monitor the fuel-burning efficiency of the cylinders and send the data to the engine control unit.

What is Sensor 2 of an Engine?

Sensor 2 of an engine is the oxygen sensor located after the catalytic converter. It is also known as a downstream sensor. Sensor 2 is what the vehicle uses to monitor the air-fuel ratio coming out of the catalytic converter to ensure the catalytic converter is functioning properly.

New exhaust system with catalytic converter.

How To Locate Sensor 1 And Sensor 2

Oxygen sensors in engines are located in relation to the catalytic converters. Sensor 1 is always located before the catalytic converter regardless of which side of the engine cylinder bank the exhaust manifold is connected.

Sensor 2 is connected to the exhaust system after the catalytic converter. The number of sensors in engines varies with the number of catalytic converters and exhaust pipes.

How To Know What Side Is Bank 2 Sensor 1 On Your Car

Going back to our problem at hand, with this knowledge of cylinder banks and oxygen sensors, it shouldn’t be hard to know what side is Bank 2 Sensor 1 located on your vehicle.

Basically, for this error code, what the diagnostic scanner is telling you is that the fault is in Sensor 1 connected to the Bank 2 side of the engine. You will have to locate the Bank 2 side of the exhaust manifold of that bank and replace the sensor that is after the catalytic converter of the Bank 2 side.

According to our earlier discussion, that should be the sensor connected to the catalytic converter in the right-hand side exhaust manifold.

Easily Locate And Replace Faulty Sensors

We have seen what the error code Bank 2 Sensor 1 means and how to use the code given to locate the faulty sensor. We discussed the different types of banks and sensors in an engine, how they function in the engine, and how each of them can be located.

The steps discussed in this article can be used to locate any type of oxygen sensor for any type of engine, that has been picked up by the diagnostic scanner to be faulty.

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About Matthew Webb

Hi, I am Matthew! I am a dedicated car nerd! During the day, I am a journalist, at night I enjoy working on my 2 project cars. I have been a car nerd all my life, and am excited to share my knowledge with you!

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