The 2003 Ford Expedition uses two oxygen sensors, one mounted in each exhaust pipe behind the catalytic converters, to monitor the amount of oxygen in the exhaust gas. Oxygen in the exhaust causes the sensors to send an electrical signal to the onboard computer, which constantly adjusts the fuel mixture for proper performance and to control emissions. A special socket is required to remove the sensors.
Park the Expedition on level ground and set the parking brake.
Raise the front of the Expedition and support it with jack stands on each side of the frame.
Trace the exhaust pipes back from the engine toward the rear of the Expedition. There is a pipe on each side of the engine. They will join into one pipe as you go toward the rear. You will see the sensors sticking out of the exhaust pipes at the 2 o'clock position on the driver's side and the 10 o'clock on the passenger's side pipes just before the pipe bends into the "Y" where the two pipes become one.
Disconnect the oxygen sensor at the electrical connector to the wiring harness. The sensor has a 6-inch lead wire connected to it.
Place the oxygen sensor socket on the sensor by sliding the sensor's electrical lead into the slot in the socket, then placing the socket over the metal part of the sensor. Turn counterclockwise to remove the sensor.
Install the new oxygen sensor by screwing it into the hole in the exhaust pipe. Place the electrical lead in the slot and place the socket over the sensor and tighten. Connect the lead to the wiring harness.
