Are you struggling to figure out which O2 sensor or ignition coil you should replace? You are not alone. A diagnostic scanner can help you find car problems efficiently, but it can still be confusing to understand what the trouble codes actually mean.
If you have ever seen a code mentioning Bank 1 or Bank 2, and Sensor 1 or Sensor 2, you might wonder what that means. The good news is that identifying these is easier than it seems once you know the basics.
In This Article:
What is Bank 1 vs Bank 2?
Bank 1 and Bank 2 simply refer to the two sides of the engine.
- Bank 1 is the side that contains cylinder number 1.
- Bank 2 is the opposite side that contains cylinder number 2.
In most vehicles with a transverse engine, Bank 1 is usually toward the front of the car. However, this is not always the case, which is why you should never assume based on the driver or passenger side.
The easiest way to find out which side is Bank 1 is to check your vehicle’s repair manual. You may also find cylinder numbers stamped on the cylinder block or head. Remember that the front of the engine refers to the side where the crankshaft pulley is located, not necessarily the front of the vehicle.
Because engines are designed differently across manufacturers, Bank 1 can be on either side depending on where cylinder 1 is positioned. For example:
- Bank 1 includes cylinders 1, 3, 5, 7, and so on.
- Bank 2 includes cylinders 2, 4, 6, 8, and so on.
RELATED: V6 vs. V8 Car Engine – What’s the difference?
What is Sensor 1 and Sensor 2?
The sensor numbers tell you where each O2 (oxygen) sensor or exhaust temperature sensor is located along the exhaust system.
- Sensor 1 is the first sensor closest to the engine. It is called the upstream sensor because it is before the catalytic converter.
- Sensor 2 is the second sensor located farther down the exhaust pipe. It is called the downstream sensor because it sits after the catalytic converter.
In some diesel engines, there may be several exhaust sensors, such as sensor 1, 2, 3, or 4. In that case, sensor 1 is always the one nearest the engine, and the numbering continues toward the rear of the exhaust system.
FAQs
In most vehicles, the O2 sensors on Bank 1 and Bank 2 are the same part number. However, this can vary depending on the car’s make and model, or the position of the sensor. Always check your vehicle’s repair manual or contact your dealer to confirm the correct part before replacing it.
Not necessarily. Bank 1 refers only to the side of the engine that has cylinder 1. In some vehicles, that side happens to be the driver’s side, while in others it is the passenger side. Relying on this assumption can lead to replacing the wrong part, so it is best to verify by locating cylinder 1 first.
The term bank does not refer to the front or rear of the engine. It only describes which side of the engine you are looking at. Even in engines that are mounted sideways, Bank 1 is still the side with cylinder 1, and Bank 2 is the opposite side. Sensor 1 and Sensor 2 refer to the position along the exhaust, not front or rear placement.
Bank 1 and Bank 2 are not related to the exhaust or intake sides of the engine. Their position depends entirely on where cylinder 1 is located. Always confirm this information in the repair manual for your specific vehicle.
Conclusion
Understanding the layout of banks and sensors can be confusing at first, but it follows a simple pattern once you break it down. Here is a quick summary of the most common O2 sensor locations:
- Bank 1 Sensor 1: The first (upstream) sensor closest to the engine on Bank 1.
- Bank 1 Sensor 2: The second (downstream) sensor behind the catalytic converter on Bank 1.
- Bank 2 Sensor 1: The first (upstream) sensor closest to the engine on Bank 2.
- Bank 2 Sensor 2: The second (downstream) sensor behind the catalytic converter on Bank 2.
Now that you know the difference between Bank 1 and Bank 2, and Sensor 1 and Sensor 2, you can identify exactly which O2 sensor needs to be replaced. Taking the time to verify this information will save you money, prevent mistakes, and improve the accuracy of your diagnostics.
If you found this guide helpful, be sure to check out our related articles and follow us on YouTube for more car maintenance tips and repair advice.
So would the upstream o2 sensors on at 2003 Ford thunderbird be under the car on the exhaust manifold is it easy to get to? Without a lift.
I have a 2007 Sienna Van. The check engine light stays on. Motor is a 3.5. Error codes given by Auto store is P0300, P0137 and P2196. Can you tell me what sensor parts I need to purchase to correct the engine light?
Thank you
I’m getting code p0449 and code p0420 on a Chevy suburban 5.3 what’s the best way to trouble shoot the problem and the traction control light keep coming on last time this happened I replaced spark plugs and was fixed months passed came back so I replaced spark plugs and wires but still running ruff…. please help point me in the right direction if possible thanks and God bless
Thanks to this information. I am asking how to test o2 sensor with multimeter thanks again…
You are wrong on Your V8 and V6 cylinder numbering. You’re correct that the front cylinder is # 1, but there are 2 connecting rods on each V type crank journal. GM and others place the drivers side rod in front of the passenger side rod making the drivers side cylinder about 1 inch in front of the passenger side as you show and the cylinders are numbered front to back just as an in line engine is numbered. Ford who had a V8 I believe in 1932 places the connecting rod on the passenger side in front making the front passenger side cylinder number one, and they continue with number 2,3,and 4 on the right side, and with 5,6,7,and 8 on the left. Different strokes for different folks, but we gotta follow the engineer’s lead.
I have put a bank 1 position 1 oxygen sensor on bank 2 sensor 1 and another of the same one on bank 1 sensor 1 in my 1998 ford Explorer 5.0 with 329 K on it. I read that the bank 1 sensor would try to adjust the fuel on bank one no matter where it is installed mine runs good but I am going to replace it with the correct part. Can the bank 1 position i sensor be used in bank one position 2 safely.
Sorry, should have added; Merc CLS V6 so I’m assuming 4x sensors total, B1S1, B2S1, B1S2 & B2S2.
Brilliant overview Magnus! My OBD gives P229F & P2201 codes which seems to be NOx sensors but nothing else. How to find out which one is causing problem?
Hello can you guys help me find bank 1 oxigen sensor on a chevy impala LT 2007 and where is it located i appreciate it
how about a 6 cylinder engine single exhaust with a bank 1 sensor 1 and bank 2 sensor 1, and then 1 O2 sensor after both manifolds come together but before the CAT? would that be a continuation of bank 1 (sensor 2)? along with the 4th O2 sensor after the CAT (bank 1 sensor 3?)
Thanks for the information, very helpful.
I have a 2001 toyota sienna 6 cylinder.it has 3 catalytic converters.1 one each bank in the front and 1 in the back.it only has 3 o2 sensors.1 one each front cat and 1 behind the back cat.after i changed my o2 sensors it started bringing up a p0420 code.just wondering how the sensors can distinguish between bank 1 and bank 2 with only 3 sensors and if there is a specific sensor i need to get before i change the bank 1 cat.
On the O2 sensors what is the difference between UPSTREAM AND DOWNSTREAM
I have bank 2 way out of whack from bank 1. Thing is it’s only a 4pot. Any chance this is some weird ford thing?
Hi this is William, I appreciate guys like for helping people, I meant your articule on the mattwer is very helpful, thanks a lot.
So I have a 2006 Jeep Grand Cherokee v6 I’m having trouble locating bank 1 sensor 2 it appears I have 1 sensor on my driver side and 3 sensors on my passenger side any ideas on how to pinpoint the one I need ?
hiya.
i have a audi A8 4.2TDI 2014.
my engine management light has come on With the following code.
9814- sensor 1 for exhaust temp bank 1 G235
P0544 00 039 circuit malfunction.
Can you please tell me or direct me roughly where this sensor might be or even better a part number.
i have already bought a sensor from audi and had it fitted and it was the wrong one.
thanks.
andy
Hi there i have a 2006 ford focus. Engine code is HWDA.
I have been told bank 2 sensor 2. Could you tell me were this is located.
The internet tells me the cylinders fire in order of 1-3-4-2. Not sure how true this is but thats all i have found
Thanks in advance
My reader doesn’t specify if it is sensor 1 or 2… any other way to see.
Can you use Bank 2 sensor 1 in the place of sensor 2?
Hi sir I’ve had somebody install a bank 2 sensor into my bank 1 sensor port and my car is working poorly will this cause any further problem and will the car work if If I remove the sensor 2 completely and not yet put in the sensor 1
Is one sensor just hanging in the air or are the sides mixed? If this is the case it will for sure run poorly and light up the engine light. You can’t switch the sensors between the banks, because if you do it will try to adjust the fuel on the wrong bank and cause the engine to run very poorly.
Can bank 2 sensor 1 work in the same place as bank 1 sensor 2?
Often the sensor one and sensor two is different. Check the part number and amount of wires to it. Sometimes you use a wideband sensor for the front sensor and a normal sensor for the 2nd!
Is bank 1 on a Toyato sienna the front behind the radiator or the middle piece with pipes and a curve on it?