The mission of the O2 sensor, or oxygen sensor, on a 1999 Ford Contour is to signal the computer as to the air-fuel ratio. It does so by measuring the free oxygen in the exhaust. Too much oxygen -- or a lean mixture -- generates a low voltage, and too little oxygen -- or a rich mixture -- provides a high voltage. The voltage ranges from 0.1 volt to 1.1 volts. All oxygen sensors are identical in size but differ in their wiring. The Contour has four sensors, two between the engine and converters and two after the converters. Each is a four-wire sensor with a preheater.
Instructions
- 1
Determine which of the sensors is faulty or sending an irregular signal. The oxygen sensor is the only device on the Contour that can give an ambiguous signal. This is one of the most misdiagnosed sensors on a car. This means that although the computer set a code for the oxygen sensor denoting an unusually high or low signal, it does not mean the sensor is bad. The signal is out of parameter in most cases because something in the engine is faulty.
2Plug the code scanner into the onboard diagnostics port, located under the dash to the left of the steering column.
3Turn the ignition key on without starting the engine. Depress the Read key on the scanner. Make a note of the codes displayed and turn off the key. Cross-reference the codes with the code decipher sheet for identification of the faulty sensor or irregular code. Determining which sensor is sending the signal also indicates the side of the engine that the problem is on. If the code states that the sensor preheater is defective or signal lost, the sensor is definitely bad. If the code states the signal was too high or low, the engine must be checked for problems. The sensors on a Contour are identified by the engine side or bank and their position. For instance, B1-S2 would be bank 1, which is always the side with the number 1 cylinder, and the second sensor, which would be behind the converter.
4Prepare to change the sensor once it has been identified and other possibilities eliminated. Ensure that you have the proper tools for the sensor being replaced.
5Raise the car and place a jack stand under each side on the subframe. Lower the car so that it rests on the stands.
6Locate the failed sensor and disconnect the electrical harness. Follow the wires from the sensor up to the connector and separate it from the vehicle harness. Use the proper tool, either the wrench or oxygen sensor removal socket, and turn the sensor counterclockwise to remove it.
7Apply some anti-seize compound to the threads of the new sensor but do not get the compound on anything but the threads. Install the sensor clockwise in the exhaust system and tighten the sensor just until it is snug or it will never come out again.
8Plug in the electrical harness connector. Lower the vehicle. Turn the ignition key on without starting the car. Depress the Erase key, and the scanner will clear or erase the code from the computers memory and turn off the check engine light.
