Is there a simple and fool proof way to locate which "side" of the engine Bank1 or Bank2 is on, with reference to OBDII data?

For example, you read ODBII live data and find that Bank2 Sensor2 (downstream) O2 sensor is not stable, but Bank1 Sensor2 is (duel exhaust vehicle). How can I determine for sure that the CAT on the left exhaust is bad or visa-versa?

Note this is not a question about checking the CAT (pressure test, temperature test, etc). This is about figuring out - by just looking in the car engine bay (?) which side is bank1 and which is bank2. Is this possible?

  • on some american cars b1 is on the right side of the engine. most are on the left. japanese and korean cars b1 is almost always on the left i can't think of one that is on the right. if there are ignition wires you can follow from the coil pack which is usually labeled to cyl 1. sometimes even the wires are labeled and on some chryslers the intake manifold will have markings for the banks.
    – Ben
    Commented Mar 15, 2017 at 18:56

4 Answers 4


Unplug one of the oxygen or EGT sensors and a open circuit fault bankX will appear. You can use that to determine what side is what.

  • This is an interesting idea actually. Deliberately invoking an error to help determine the side
    – Chris
    Commented Mar 15, 2017 at 20:14

You need to refer to the manufacturer's manual as I have never seen that information shown under the bonnet - but there may be a manufacturer that does provide it.

  • The rover V8 I put in my landrover had cylinder 1 on front rhs standing in front : so 1, 3, 5 & 7 on rhs and 2, 4, 6, 8 on lhs counting towards the back.
    – Solar Mike
    Commented Mar 15, 2017 at 21:06

Unfortunately, no. It depends on the car. Typically, bank 1 is the driver side, but this isn't true in all cases. For example, BMW E38 7 series has bank 1 on the passenger side. This data is not stored as a regular value in OBD-II.

You will need to research which side is bank 1 for the particular car in question.


The way I was taught, is that bank 1 coincides with the side of the engine where the #1 cylinder is. So, if your firing order on your spark plugs and wires (which go to the cylinders) starts 1 - 2 - 3 on the passenger side,(like my 1999 Ford F-150 V6 automatic), then the passenger side is bank 1, therefore the driver's side if the engine would be bank 2.

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