Bank 1 vs bank 2 O2 sensor, a lot of people are wanting to know the difference. O2 sensors are needed both before and after the catalytic converter in order to keep track of vital engine health and emissions information.
In V-configuration engines, multiple sets of O2 sensors are needed because V engines are essentially 2 inline engines mounted to one crankshaft. Bank 1 is the side of the engine that contains piston 1. Bank 2 is the side of the engine that contains piston 2. Each side of a V engine has its own exhaust manifold. In any dual exhaust system, two catalytic converters are needed. For each catalytic converter, 2 O2 sensors are required because there must be an O2 sensor both before and after the catalytic converter.
In this article, we will explain what engine banks are and how they are arranged. We will also go over what a catalytic converter is, and why 2 O2 sensors are needed for each catalytic converter.
Bank 1 is the side of the engine that has piston number one. For example, If you have a V6 engine, pistons 1, 3, and 5 are going to be on one side and pistons 2, 4, and 6 are going to be on the other side.
For a V8 engine, it works the same way. Cylinders 1, 3, 5, and 7 will be one on one side of the engine and cylinders 2, 4, 6, and 8 are going to be on the other side of the engine.
So, if you are having a problem with an O2 sensor in bank 1, and cylinder one is on the driver side of your engine, then you know you have to take a look at one of the O2 sensors on the driver side of the vehicle.
If you are not sure which cylinder is cylinder 1 in your vehicle, the best thing you can do is consult your vehicle’s manual. It will have a diagram in there somewhere that shows which cylinder is cylinder 1.
A catalytic converter has to have an O2 sensor both up and downstream. O2 sensor 1 is the most upstream sensor (the o2 sensor that is closest to the engine). O2 sensor 2 is the most downstream sensor (the o2 sensor that is closest to the tailpipe).
If your engine’s number 1 cylinder is on the driver side of your vehicle, then O2 sensor bank 1, sensor 1 will be located in the exhaust pipe on the driver side of your vehicle between the catalytic converter and the engine.
If your vehicle’s cylinder number 1 is on the driver side of the vehicle, that means O2 sensor bank 1, sensor 2 is going to be in the exhaust pipe on the driver side of the vehicle between the catalytic converter and the tailpipe.
As long as your engine’s first cylinder is on the driver side, then that means your engine’s number 2 cylinder is going to be on the passenger side.
So, O2 sensor bank 2, sensor 1 is going to be in the exhaust pipe on the driver’s side of your vehicle between the catalytic converter and the engine.
If cylinder 2 is located on the passenger side of the vehicle, O2 sensor bank 2, sensor 1 will be located in the exhaust pipe on the driver’s side of your vehicle between the catalytic converter and the tailpipe.
The above is only true for longitudinally mounted engines (engines that are mounted front to back).
In a transversely mounted engine, engines are mounted left to right. So, that means the banks will be front and rear banks rather than driver or passenger side banks.
How To Locate Your Oxygen Sensors?
Method 1: The Manual Method of Locating Oxygen (O2) Sensors
Step 1: Find Bank 1 and Bank 2
We have explained what bank 1 and bank 2 means in the previous section of the article. If you want to locate the different banks and sensors in your car engine system, you must first understand the type of engine you have.
Generally, there are two types of engines, transverse engine, and inline engines. Most manufacturers mount transverse engines in the opposite direction. If you know how to identify the different types of sensors, the design or mounting of your car engine may not cause you any trouble.
As mentioned earlier, bank 2 will always be on the cylinders marked with even numbers like 2, 4,6,8,10,12, and so on. Alternatively, you can find bank 1 on cylinders marked with odd numbers like 1,3,5,7,9,11, etc.
Step 2: Locate the Cylinders
Once you’ve identified bank 1 and bank 2 on your car engine, the next challenge is to locate the different cylinder numbers. Here is how you can go about it.
In some cases, the ignition cables used to connect the cylinders may have the cylinder numbers marked on them. However, if you repaired your engine before, it is not wise to use the cables in identifying the cylinders – your mechanic may have replaced them in different positions.
Check the crankcase cover if there is a cylinder number written or stamped there.
Look up your repair manual or service manual for the order of cylinders. This is the safest way of locating the cylinders. If you don’t have your user manual, you can ask your car dealer for help.
If you have your engine code or cylinder order, you can search for the information on the internet.
Step 3: Find the sensor numbers.
The last step is to find the sensor numbers, and that means you should be able to tell the different types of sensors in your car engine.
A sensor number tells you where the oxygen sensor or the exhaust temperature sensor is mounted on the exhaust system. Sensor 2 is normally located at the rear of the vehicle’s exhaust system, while sensor 1 is located the closest to the engine.
You can also say that sensor 1 is found before the catalytic converter front, while sensor 2 is located after the catalytic converter front. That is why sensor 1 is also known as the upstream O2 sensor, and sensor 2 is known as a downstream O2 sensor.
In some cases, a vehicle may have up to 4 sensors (for instance, cars with diesel engines) because they have a lot of exhaust temperature.
If you have a diesel engine with four O2 sensors, you will find sensor 1 nearest to the car engine and sensor 4 furthest to the car exhaust system.
Method 2: Using OBD Scanner to locate Oxygen (O2) Sensors
It is much easier and faster to locate oxygen scanners in your car engine with an OBD scanner at your disposal. Follow these steps to find out bank 1 and bank 2 in your car engine.
- Connect the OBD scanner and erase all the trouble codes in the device.
- Countercheck that no trouble code is left
- Unplug one of the O2 sensors (it doesn’t matter which one you choose) then proceed to check the DTC code.
The DTC code will tell you which one is bank 1 and which one is bank 2. You can easily tell which one is your bank 1 or bank 2.
Using the OBD scanners is one of the safest ways to identify oxygen sensors in your engine and ensure you replace the right ones. Sometimes you may get a DTC code P0420, which is normally triggered by a fault in the oxygen sensors.
In this case, you have to troubleshoot the o2 sensor and fix the errors. A leak in the exhaust system is likely to be the cause of this error code. Ensure you fix it before you can proceed to locate the oxygen sensors.
How to know if you should replace your Car Oxygen Sensors
There are many ways you can tell if your car needs a new oxygen sensor. When you see a check engine light on the dashboard, it could mean that there is a serious issue with your car that needs immediate fixing.
If you drive to a mechanic shop, they can inspect your car and find out the reason your check engine light is on.
Other signs that you need to replace your car’s O2 sensors include:
- Misfiring spark plugs.
- Rough idle.
- High gas emissions from the vehicle.
- An increase in fuel usage per mile.
- Your vehicle has covered over 60,000 miles.
Ideally, replacing your oxygen sensors plays a critical role in reducing the amount of fuel your car consumes by at least 40%.
Take your vehicle through an emission test, if it fails, then it means there is o2 sensor problems, and you need to replace them immediately. A faulty oxygen sensor is a reason most vehicles have exhaust system issues.
Most vehicles come with an emissions warranty that may determine when you are likely to replace your vehicle’s oxygen sensor. However, in most cases, the oxygen sensors will outlast the warranty.
Vehicle manufacturers recommend that if you have heated oxygen sensors (used in the 1980s and 1990s), you should replace them after covering 60,000 miles. If you are driving in a modern vehicle, you should replace the O2 sensors after covering at least 100, 000 miles.
The truth is that if you maintain your vehicle’s engine well, the oxygen sensors can last the lifetime of the vehicle. That is, you can cover over 250,000 miles before replacing the oxygen sensors.
As your car ages, so do your oxygen sensors. Oxygen sensors degrade with time, depending on how you use fuel and how you maintain your vehicle engine.
Sulfur, an element found in crude oil, is responsible for the degradation of oxygen sensors. Therefore, when fueling your car, you should go for fuel with a low sulfur concentration. Sulfur concentration in the fuel will determine directly how long the oxygen sensors are going to last.
How To Test Oxygen Sensors
Bank 1 vs Bank 2 O2 Sensor. It can be confusing if you are not familiar with engine layouts. Bank 1 just means the side of the engine that cylinder 1 is on.
So, in the case of a V8 engine, Bank 1 Sensor 1 is the O2 sensor closest to the engine that is on the same side of the vehicle as cylinders 1, 3, 5, and 7. Bank 1 Sensor 2 is on the same side of the vehicle, but it’s the one that’s furthest from the engine. Bank 2 Sensor 1 is the O2 sensor that’s furthest from the engine and on the same side of the vehicle as cylinders 2, 4, 6, and 8. Bank 2 Sensor 2 is on the same side, but it’s the O2 sensor that is furthest from the engine.
We hope this article helped you gain a better understanding on Bank 1 vs Bank 2 O2 sensors. Thanks for reading!
I’m William Guzenski, ASE certified master automobile technician & automotive expert. I love to attend race events and car shows throughout the country. I also loves to travel 40-foot motorhome, exploring abandoned mines and ghost towns. I’m currently building another car for Bonneville Salt Flats and will be campaigning a drag car at several events.