If you’re new to the 3MZ V6 of the Lexus (or most other V6s for that matter), you’d be confused when a scan tool indicates that you need to check ‘bank 1’ for something or that some challenge exists on the first cylinder of your engine (usually found on bank 1).
For example, if you get a P0420, interpreted to mean: ‘catalyst system efficiency below threshold bank 1’, you may be naturally confused about where to look. Where is bank 1 on your engine or where is the second bank (relative to it)?
Below, I’ll explain how to easily identify where the first bank of an engine is. However, to do this in a manner that will stick, I’ll need to explain some concepts first.
Article Outline
Transversely or Longitudinally Mounted Engines
Without first understanding how engines are mounted in a car, understanding the concept of ‘bank 1’ is going to take a while – and is definitely going to confuse you, instead of illuminating things.
Most mainstream vehicles today have their engines mounted either transversely or longitudinally. If you drive a regular sedan, SUV, CUV, coupe, or convertible, great chances are that you have either of these setups.
Transversely Mounted Engines
A transversely mounted engine is mounted side to side across the hood, with the crankshaft perpendicular to the direction of travel of such a vehicle. This means the engine sits across the width of the engine bay.
In most front wheel drive (FWD) vehicles, this is the default set up as it saves on space and makes everything compact.
In this type of setup, ‘Bank 1’ is the bank of cylinders closest to the firewall. The firewall side is the part of the engine bay closest to the dashboard of the vehicle.
Longitudinally Mounted Engines
A longitudinally mounted engine is an engine mounted (and running) from the front to the back of the vehicle, with the crankshaft positioned parallel to the direction of travel of such a vehicle. This means the engine fits along the length of the engine bay area.
Most rear-wheel drive (RWD)/Four/All Wheel Drive (4WD/AWD) vehicles have this as the default setup as it offers better weight distribution and importantly, allows larger engines (such as V8s and V12s) to easily fit into the engine bay.
In this type of setup, ‘Bank 1’ is the bank of cylinders on the driver’s side of the engine.
Remember that since these engines run longitudinally, there are technically no ‘firewall’ and ‘radiator’ sides. Instead, what is obtained is the ‘driver’ and ‘passenger’ sides. Bank 1, the bank housing cylinder number 1, is usually on the driver’s side of the vehicle (on the left-hand side of the car).
It’s important to give context here. When I say ‘driver’s side of the vehicle’, what I’m referring to is the traditional setup of a typical left-hand drive vehicle where the driver sits on the left.
This is why ‘left-hand side’ is used synonymously with ‘driver’s side’ of the engine (all assuming a forward, seating position in the vehicle, of course).
Left or Right? Radiator or Firewall?
Getting to figure out where ‘Bank 1’ is on any given vehicle can be a challenge, especially for the beginner DIY mechanic or a car owner who needs to run some simple procedures on their car.
However, the simple rule of thumb (at least for traditional vehicles), is to figure out if the engine is mounted either transversely or longitudinally.
A transversely mounted engine will have its cylinders clearly by the firewall and radiator sides while a longitudinally mounted one will have its cylinder on the left and right of the vehicle.
For most transversely mounted V6/V8 engines, bank 1 will be at the firewall side of the engine; for most longitudinally mounted engines, bank 1 will be on the left, or driver’s side of the engine.
Remember this and you’ll NEVER get confused again. That said, ‘bank 1’ can (actually) be ‘anywhere’…
‘Bank 1′ Can Be Anywhere…
Scan tools are computers and computers aren’t always right. In this regard, ‘bank 1’ can (actually) be ANYWHERE.
Sounds confusing? Allow me to explain.
Most engines today have only one bank: i4 and straight 6s being very popular examples.
However, when the scan tool points you to bank 1, it’s simply referring you to the only bank the vehicle has – so you need to simply focus on the only bank there is since there’s no other bank to alternatively check/contemplate.
In this case, the cylinder count starts from the left to the right (in most cases) – if what you’re looking for is cylinder-specific.
Where Is the Bank 1 on the 3MZ V6 Engine of the Lexus ES330?
The Bank 1 position on most FWD V6 engines including the 3MZ-FE on the Lexus ES330 is on the firewall side of the engine bay.
The firewall side of the engine is the part of the engine closest to you (or better still, closest to the dashboard of the vehicle).
Note that, this configuration may be slightly different on models that aren’t V6, made by Lexus, mounted longitudinally, and importantly, aren’t the Lexus 3MZ-FE powering the ES330.
To be certain, always check your owner’s manual and workshop guides for the exact (cylinder) positioning of an engine.