Finding an Oxygen Sensor in the Exhaust System
In the early 1980s, when vehicle manufacturers began to install on-board diagnostic (OBD) systems,oxygen sensorsbecame part of the computerized emission control system. Oxygen (O2) sensors measure the amount of oxygen in the exhaust gases to help the computer better optimize the air/fuel mixture and reduce emissions. Modern vehicles can have up to five or more oxygen sensors, depending on make and model. Therefore, knowing where to find each oxygen sensor in your vehicle will help you decide when to replace them according to the interval suggested by your car manufacturer.Oxygen sensor LocationBefore 1996, US vehicle models came out equipped with the first generation of the *on-board diagnostic(OBD-I) system. This system uses one oxygen sensor-also known as the primary sensor-to monitor oxygen content in the exhaust gases coming out of the engine through the exhaust manifold.The exhaust manifold attaches to one side of the cylinder head and has a series of pipes that bolt to the engine. At the other end, the manifold attaches to the header pipe. To better do its job, the oxygen sensor-a small cylinder about the size of a spark plug-mounts on the exhaust manifold itself or the header pipe. This sensor can have one or more electric wires that connect to the computer, depending on vehicle year.Starting with the OBD-II (second generation) system in 1996, car manufacturers began to install more oxygen sensors. Now, later vehicle models can have up to five or more O2 sensors. You can find theprimary sensorin its usual place. To find the other sensor(s), you need to follow the header pipe that connects to the exhaust manifold towards the other end. Right before the catalytic converter, you'll see the secondary sensor. This sensor also monitors oxygen content in exhaust gases.However, other O2 sensors work as catalytic converter monitors. You can find these monitors on the intermediate pipe that connects between the converter and the muffler of your car. These sensors report to the car's computer by sending an electric signal, which the computer compares to other oxygen sensors' signals to check whether the converter is working as it should.Whatever your vehicle model, you can easily find the oxygen sensors in the exhaust system. However, if your car has more than one sensor, you'll need to raise the vehicle to get access to downstream sensors for service. If necessary, use the service manual for your particular vehicle make and model to find those sensors hidden from view. Most public libraries keep a copy of this manual in their reference section.
