It is the Ford oxygen sensor that enables your onboard computer to make the correct adjustment to the air to fuel ratio so your engine can perform at its maximum level. It is not the only sensor on your engine, but its information is vital for a smooth running vehicle. The placement of the oxygen sensor is behind the engine under the hood of your Ford, on the exhaust pipe close to the exhaust manifold. There is probably one located before and one located after the catalytic converter. The actual signal the oxygen sensor sends to the onboard computer is the current ratio of oxygen in the exhaust gases from your engine to what is present in the atmosphere around your vehicle. This is how your Ford can run smoothly no matter what altitude you are driving at. Like all other sensors, the driver will become aware there is a faulty part when the check engine light pops on in the dash console. This includes the failing of the oxygen sensor. The code that is stored in the onboard computer then has to be retrieved and deciphered to determine the appropriate course of action required to fix your Ford vehicle. The failing Ford oxygen sensor has a specific code when it malfunctions. This code is not the same for each model, so a repair manual that is specific to your model and year is required to diagnose this problem. These manuals can be purchased at most local auto parts stores. Because this is an electrical component, the battery should be disconnected before the oxygen sensor is replaced. This disconnecting of the battery also wipes clear all of the codes your onboard computer has stored. For this reason, if there is more than one code they all should be recorded before the battery is disconnected.