There’s no way you won’t begin sweating if your OBD II code reader indicates a challenge with one of your vehicle’s sensors and simply tags it ‘bank 1 sensor 2’. This is particularly true if you’re a new car owner.
The challenge will certainly take another dimension if you have no idea what ‘upstream’ or ‘downstream’ means when dealing with banks, sensors and codes.
Luckily, it isn’t that deep and today, I’m going to explain all what the jargon, bank 1 sensor 2 means to you like you’re in grade school. At the end of the article, the plan is that you’ll NEVER again be confused when you’re faced with sensors, their positions and importantly, what it all means.
First things first however: take a look at what bank 1 sensor 1 means before we proceed to address the issue of the second sensor on the same bank.
Article Outline
Where Does the Term ‘Bank 1 Sensor 2’ Apply?
First and foremost, it’s important to understand that the term, ‘bank 1 sensor 2’ applies to oxygen sensors (sometimes called ‘O2 sensors’).
The above clarified, it’s very important to note that when this term is used, the intent is exclusively tied to O2 sensors and nothing else.
With that out of the way, what exactly does an O2 sensor do?
What Does an Oxygen (O2) Sensor Do?
An O2 sensor is responsible for metering the oxygen the air intake receives and relaying this information to the Engine Control Module (ECM) to determine how much fuel to order the injectors to spray for that particular driving condition.
However, not all oxygen sensors are meant to work this way: some have the singular duty of checking the level of unburned oxygen in the exhaust fumes after combustion.
For such types of oxygen sensors, their primary function is emission control, not fuel-mixture ratios or even vehicle efficiency (in the strict sense).
So, why is more than one O2 sensor needed for a modern ICE in the first place?
The reason, it turns out, is simple and straight to the point.
Why Is More Than One O2 Sensor Needed?
Two oxygen sensors are needed, usually, per bank of an engine. This means that, for vehicles with two banks, four O2 sensors make up its design.
The first sensor on the bank is usually the one focusing on air-fuel ratios. It feeds the ECU information relating to the oxygen in the air it detects. The ECU in turn uses this information to determine how much fuel to order the injectors to spray, in a closed-loop fashion.
Without this type of ‘work relationship’, the vehicle will be in an open loop all day and fuel efficiency will suffer greatly.
However, the second oxygen sensor, the one after the catalytic converter, doesn’t deal with air-fuel ratios. Instead, its job is strictly emissions control and a check to see if the catalytic converter is doing its job.
So, two oxygen sensors per bank: one for air fuel-fuel ratios and a second to check if the catalytic converter on that bank is doing what it ought to do.
Where Is O2 Sensor Bank 1 Sensor 2 Located?
The O2 sensor on bank 1 sensor 2 is located after the catalytic converter, on the first bank of an engine with two banks. Its duty is strictly to monitor the catalytic converter on that bank to ensure it’s working as it should.
On a FWD-biased vehicle with a transversely mounted engine, this sensor will be the second oxygen sensor, after the cat, on the bank closest to the firewall.
On AWDs, 4WDs, RWDs, etc with longitudinally mounted engines, this sensor will be the second sensor after the catalytic converter on the side of the driver or the left-hand side of the vehicle.
Is Bank 1 Sensor 2 Upstream or Downstream?
Bank 1 sensor 2 is a downstream oxygen sensor. As I’ve already explained, its duty is to make sure that the catalytic converter on the bank it serves is doing its job.
The first sensor on any given bank, ‘sensor 1’ is upstream – and is responsible for air-fuel mixtures with ‘sensor 2’ on any given bank responsible for monitoring the aftermath of combustion (i.e. how well the catalytic converter is doing its job).
Wrap Up
Knowing your sensors and what they’re up to in your vehicle is the first step to becoming a responsible vehicle owner. It’s also the first step to becoming a good auto DIY mechanic as these are the basics that inspire a foundation in motor repair.
Understanding your banks (in addition to the sensors on it) is the full picture…once you grasp the idea that EVERYTHING on an ICE relies directly (or indirectly) on the concept of banks, then, your mechanic training is more than half complete.
Seriously.
This is an ongoing series. The next article is: Bank 2 sensor 1: upstream or downstream?