The 2005 Ford Expedition has two oxygen sensors. One will always be located forward of the catalytic converter and one behind. The forward sensor signals the free oxygen in the system relative to the fuel mixture. It also is used for a comparison of the trailing sensor behind the converter. There should be significantly fewer counts on the rear sensor than the front, indicating that the converter is working. When the counts are close to the same, that means that what goes into the converter comes out unchanged. A code scanner is the only way to determine which sensor is malfunctioning.
Plug the code scanner into the OBS port on the lower left side of the steering column below the dash. Turn the ignition key to the “On” position without starting the engine.
Press the “Read” key on the code scanner, which interrogates the computer for failure codes and displays them on the scanner. These codes are faults in the electrical elements under the control of the computer, exclusive of mechanical aspects. The codes are displayed as a letter followed by four numbers. The letter designates the computer control quadrant and the numbers represent specific failure descriptions.
Record this code and cross-reference it with the code sheet that accompanies the scanner. Here is an example of an oxygen sensor code: 02 (oxygen sensor) – B1 (bank 1) – S2 (sensor number 2 or behind the converter). Bank 1 is displayed even on 4 cylinder engines though there is only 1 bank. On all others such as V6 or V8 engines, bank 1 relates to the side of the engine where the number 1 cylinder is located.
Raise and support the truck on jack stands. Locate the indicated sensor. Disconnect the electrical harness connector. Remove the oxygen sensor, using the 7/8-inch wrench.
Spread anti-seize compound on the threads on the new sensor. Screw the sensor in, and tighten the sensor with the wrench. Turn the ignition key on. Press the “Erase” key on the code scanner to turn off the check engine light and reset the computer.
