Whether you’re using one of the most expensive scan tools available on the market today or are relying on an affordable code reader, sooner than later, the tool will point you to ‘bank 1 sensor 1’ – and if you don’t already understand this jargon, you’d be thoroughly confused if this is an upstream or a downstream ‘arrangement’.
Or, if my guess is right, you’re already in need of the exact location and sweating at the moment. For you, this isn’t a matter of probability: you need the location of the bank 1 sensor 1 and you need it NOW.
Fair enough, I’ll share with you the exact location of bank 1 sensor 1 and importantly, clarify the instances where the location of this may come up.
I’ll also explain where this location is on a V6/8 and also, commonly, on the i4 engines. If you’d rather skip these and go straight to what you’re looking for, consider using the article outline below.
Before you proceed too, you may wish to read how to positively identify bank 1 on an engine.
Article Outline
Where Does the Term, ‘Bank 1 Sensor 1’ Apply?
The term ‘bank 1 sensor 1’ applies when talking about oxygen (O2) sensors. It refers to the unique position of a sensor on the bank, whether it’s upstream or downstream relative to the catalytic converter.
It’s interesting to note that, because of the oxygen sensor’s unique task, it remains the only sensor in a modern automobile that deploys the nomenclature ‘bank 1 sensor 1’.
What Does an Oxygen (O2) Sensor Do?
An O2 sensor measures the amount of oxygen in the air intake system of a vehicle for air-fuel mixture ratio purposes.
Oxygen is sucked in from the air intake, filtered by the air filter, and fed into the combustion chamber via the intake manifold.
Without the reading from the oxygen sensor, the Engine Control Unit (ECU) will remain clueless as to the quantity of fuel to ‘authorize’ for that cycle, factoring the driving conditions and best economy in mind (for the situation).
The failure of this oxygen sensor will usher in the dreaded Open Loop (OL) condition, firing several other symptoms along the way with the most noticeable being poor MPGs.
The above details the reality of the first O2 sensor, before the catalytic converter. The actual task of the O2 sensor after the cat is a bit different from what has been explained above.
The oxygen sensor after the catalytic converter has no business with air-fuel ratios or fuel economy. Instead, it deals with emissions strictly, checking the content of unburned oxygen post the catalytic converter (on that bank).
Why Is More Than One O2 Sensor Needed?
More than one oxygen sensor is required per bank of an engine: there’s always a pre-cat O2 sensor and also, a post-cat O2 sensor.
For most engines, it’s two oxygen sensors per bank, one pre and another, post-cat. This means that, for V6s (and most engines with more than one bank), each bank will have a set of two O2 sensors, a pre and post-cat oxygen sensor.
That said, this isn’t a hard and fast rule: manufacturers are always playing with the limit of what’s possible so expect some vehicles to have a slightly different configuration from what I just shared above.
Where Is O2 Sensor Bank 1 Sensor 1 Located?
The bank 1 sensor 1 oxygen sensor is the first sensor on the first bank of an engine, pre the catalytic converter of that engine bank.
As I explained here, ‘bank 1’ is usually on the firewall side of an engine (on a transversely mounted engine) and on a longitudinally mounted engine, bank 1 is usually on the driver’s side (or left).
Applying the above logic here, the O2 sensor fitted in the ‘bank 1 sensor 1’ location would be the oxygen sensor before the catalytic converter on the firewall side (FWDs majorly), and for 4WDs, RWDs, etc., that would be the first O2 sensor before the catalytic converter on the driver’s side (or left).
Is Bank 1 Sensor 1 Upstream or Downstream?
Generally, bank 1 sensor 1 is upstream. It is referred to as the ‘upstream’ sensor because of its relative position to the other O2 sensor on the bank, the one after the catalytic converter called the downstream sensor.
Wrap Up
Knowing where your sensors are located and importantly, what they do in an engine is an integral part of keeping your vehicle running in top condition and importantly, getting the best your ride offers.
It is also key to using and understanding an OBD II scanner/code reader when you have to (which should be often).
Fortunately, this remains one of the easiest steps on the auto DIY journey.
This is an ongoing series. The next article is: Bank 1 sensor 2: upstream or downstream?