FAQ – What is an Oxygen Sensor?

FAQ – What is an Oxygen Sensor?


Chances are if you need to learn what a oxygen sensor is, there’s a problem with your vehicle. The oxygen sensor is also known as the 02 sensor or air fuel ratio sensor. This sensor is mounted in your exhaust stream, and reads the exhaust gases coming out of your engine.

The oxygen sensor reads how much oxygen is present and the fuel ratio in your exhaust. This information is sent to your engine computer, and is used to determine how rich or how lean your engine is running. The engine computer is also known as the Powertrain Control Module or PCM.

Your PCM is constantly trying to reach an optimum air fuel ratio when your engine is running. Your engine computer is responsible for increasing or decreasing the fuel delivery through the fuel injectors, in order to reach close to 14.7:1 air fuel ratio. This number represents 14.7 parts air to 1 part of fuel or 14.7:1. This point is also known as the stoichiometric point for your combustion engine.

This is known as closed loop control, where your engine computer is constantly trying to reach stoichiometric efficiency. There’s typically more than one oxygen sensor in your vehicle, and they have different roles depending on which one you are talking about.


How To Change your Cadillac ATS Oxygen Sensor

The upstream oxygen sensor is the primary 02 sensor, the downstream oxygen sensor is known as the secondary 02 sensor. Vehicles built after 1991 have two 02 sensors, one to provide fuel injection information to the engine computer, and the other to ensure that your catalytic converter is still working.

Your 02 sensor output is what your PCM or ECU uses to alter and adjust the fuel deliver. This promotes proper catalyst efficiency and optimum fuel efficiency for maximum gas mileage.


OEM 02 sensors are built with the highest quality and designed for superior performance. Air fuel ratio sensors are often connected by way of a four pin weatherproof connector to ensure proper fit and a long life of service.

It’s not common for air fuel ratio sensors to simply up and fail overnight, although it can happen. Usually your 02 sensor fails over time, as it becomes fouled and loses the capacity to read exhaust gases. When this happens your oxygen sensor becomes lazy, and can send false rich signals to your engine computer. This can cause your engine to run lean ( or not enough fuel ) which can cause premature damage and over time lead to catastrophic engine failure.

Why you should replace your Oxygen Sensor

The reasons behind replacing this sensor are too numerous to list really. Not only does this unit ensure that your engine runs efficiently and fuel economy, which saves money but it can also save your catalytic converter. When your engine runs overly rich or lean, your spark plugs won’t last which in turn leads to more money and service that’s required.

The catalytic converter in your car, truck or van is intended to cut down on emissions. This is an expensive part, as it’s comprised of highly expensive metals and filtering agents. Some of these elements include but are not limited to platinum, rhodium and palladium.

When there’s an excessively rich condition in your engine, or there’s a lot of unused fuel or hydrocarbons present, it can overpower your catalyst. When your engine runs rich, this excess of hydrocarbons elevates exhaust gas temperatures. This increase in exhaust temps will lead to a meltdown of your three-way catalyst and a failed converter.

When your catalytic converter fails or becomes clogged due to excessive hydrocarbons, it will require replacement. Avoid this by shopping for an 02 sensor replacement when you have a check engine light or suspect an issue with your air fuel ratio sensor.