How to: Oxygen Sensor Replacement in a '96 Ford Aerostar

The oxygen sensor is the most misdiagnosed sensor on a 1996 Ford Aerostar. The oxygen sensors serve primarily as a final fuel trim signal for the computer to regulate the stoichimeteric fuel ratio within a parameter that will allow as complete combustion as possible in the converter. It is true that it affects the fuel mixture, but not drastically enough to notice but for the check engine light and a slight decrease in fuel economy. Generally an O2 sensor will last at least 100,000 miles as long as no outside influence is presented, such as a poor state of tune on the engine, plug misfire, vacuum leaks or leaking fuel injectors.

Instructions

1

Determine which sensor is in question and what type of problem it is experiencing. Plug the code scanner into the onboard diagnostics, or OBD, port under the dash to the left of the steering column.

2

Turn the ignition key to the ON position without starting the engine. Depress the Read key on the scanner. Make a note of any or all of the codes displayed on the scanner.

3

Cross-reference the codes with the code sheet to determine which sensor is involved. The two oxygen sensors are numbered 1 or 2. The number 1 means the sensor is between the engine and the catalytic converter. The number 2 means the sensor is behind the converter between the converter and rear of the car. The code will go further to explain the problem that it has sensed from the oxygen sensor. A code stating that the preheater is defective (most common) is non-correctable without replacement.

4

Turn off the ignition switch. Raise the van and place a jack stand on both sides of the van under the subframe. Lower the van so it rests on the stands.

5

Locate the sensor indicated by the code. Disconnect the electrical connector by tracing the wiring harness from the sensor up to the connector. Use the wrench or socket and turn the sensor counterclockwise to remove it from the exhaust.

6

Coat the threads on the new sensor with anti-seize compound that meets Ford specification ESE-M12A4-A. Insert the sensor into the threaded hole in the exhaust and tighten it to between 27 and 33 foot-pounds with a torque wrench and oxygen sensor socket.

7

Connect the electrical harness connector. Lower the van. Turn the ignition key on again. Depress the Erase key and the scanner will turn the check engine light off and clear the code from memory.