You probably don't spend much time thinking about your O2 sensor. Until you have problems with your vehicle that could be caused by your oxygen sensor, you might not think about it at all. The oxygen sensor, or O2 sensor, plays a key role in your vehicle’s performance; it measures the amount of oxygen that is mixed with the exhaust gases, which helps the engine computer monitor performance of the engine.
What the O2 sensor does
The job of the O2 sensor is to tell your car's computer how much oxygen is present in the system. The right mixture of fuel and oxygen provides the best efficiency for the engine, so the O2 sensor signals for fuel to be either added or taken away to reach the proper levels.
Locations of the O2 sensor
In most cases, the oxygen sensors are located in the exhaust manifold of the vehicle, which is part of the engine. Even within this area, placement can vary. For instance, some oxygen sensors may be on the exhaust pipe while others are located on the front of the manifold. Sometimes, dual oxygen sensors are located in the exhaust collector, where exhaust multiple pipes combine into one to exit the vehicle. Sensors may also be found at the outlet of the catalytic converter or at the inlet. They are named the pre-catalyst and post catalyst oxygen sensors.
Most vehicles have two or four sensors but some have odd numbers, like one or three. The placement of the oxygen sensors varies by manufacturer and model. For instance, Ford full-size trucks and vans will have one positioning for 4.2 liter engines and another for 5.0-liter engines. GM trucks with 5.0-liter engines won’t be the same as for Ford models.
It’s important to know how many O2 sensors your vehicle has and where they are located before you begin any testing.