Bank 1 vs Bank 2 – Sensor 1 & 2 – O2 Sensor Location

The logic of finding the right O2 sensor to replace. Engine Banks and sensor location.

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Are you struggling to discover which O2 sensor you should replace?

You are not alone! Everything with bank 1, bank 2 sensor 2, etc., can be confusing when diagnosing your car.

It is actually not that difficult! Let’s find out!

What is Bank 1 vs Bank 2?

Bank 1 Vs Bank 2

Bank 1 vs Bank 2 refers to different sides of the engine. Bank 1 is the side with cylinders 1, 3, 5, 7. Bank 2 is the side with cylinders 2, 4, 6, 8.

The easiest way to discover the right cylinder bank is to check your car’s repair manual. You can also try to find any stamps on the cylinder block or head for any cylinder numbers.

The front of the engine is the part where the crankshaft pulley is. The side nearest the front is not the front of the engine.

You can’t simplify it and say that bank 1 is on the driver’s side or vice versa because different engines can have cylinder 1 on different sides. We drive on different sides globally, so it’s just confusing and misleading to guess which side bank 1 or bank 2 is on.

  • Bank 1 is the side with the number 1 cylinder (Cylinders 1 – 3 – 5 – 7 etc.)
  • Bank 2 is the side with the number 2 cylinder (Cylinders 2 – 4 – 6 – 8 etc.)

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What is Sensor 1 & 2?

Bank 1 Vs Bank 2

The sensor number tells us where on the exhaust system, the O2 sensor or the Exhaust temperature sensor is installed.

The 1st sensor is located closest to the engine, and the last is located towards the rear of the exhaust system.

Generally, if we are talking about O2 sensors:

Some diesel engines have many exhaust temperature sensors, and they can use sensors 1 – 2 – 3 – 4, etc. In this case, sensor 1 is nearest to the engine, and the last sensor in the exhaust system’s rear.

Bank & Sensor Conclusion

O2 Sensor On Cat

Bank 1 Sensor 1 is the first sensor closest to the engine. On Bank 1 means it is at the engine side with cylinders 1, 3, 5, 7, etc.

Bank 1 Sensor 2 is the second sensor on the engine’s exhaust pipe, usually behind the catalytic converter. On Bank 1 means it is at the engine side with cylinders 1, 3, 5, 7, etc.

Bank 2 Sensor 1 is the first sensor closest to the engine. On Bank 2 means it is at the engine side with cylinders 2, 4, 6, 8, etc.

Bank 2 Sensor 2 is the second sensor on the engine’s exhaust pipe, usually behind the catalytic converter. On Bank 2 means it is at the engine side with cylinders 2, 4, 6, 8, etc.

Written by: Magnus Sellén

Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.