Check Engine Light Problem on a Ford Expeditionby Jeffrey Caldwell
Vehicles built after 1996 such as the Ford Expedition utilize a system known as On Board Diagnostics (OBD II) to monitor the performance of emissions components. When one of the emissions components fails, it send a trouble code to the engine computer, which in turn sends a signal for the check engine light on the dash to illuminate.
Diagnostic Code Scanners
To determine which emissions component has caused the check engine light to illuminate, you will need a diagnostic code scanner. Scanners come in two basic types, handheld units, and cables that work with software installed on a computer. Either type will work to read and clear trouble codes from your engine's computer. If you intend to purchase a code scanner, make sure it will work with the specific make, model and year of your vehicle. Some scanners are universal, while others will only work on specific brands. If you don't plan to use a code scanner much and don't wish to purchase one, many automotive parts stores will read and clear trouble codes at no cost.
Reading a Trouble Code
Plug the scanner into the diagnostic port or your vehicle. On the Expedition, this port is located on the driver's side of the vehicle underneath the dash. Insert the key into the ignition and turn it to the "run" position. Do not start the engine. The scanner will not be able to read most trouble codes while the engine is running. Specific instructions for using the diagnostic scanner will vary by manufacturer. Most will have a "Search for trouble codes" or similar button. Press this button to check the engine's computer. Wail a few minutes until the scanner finds the trouble code.
Decoding Trouble Codes
While the diagnostic code scanner will give you the relevant trouble code that causes your check engine light to come on, it will not give you an explanation of what the code means. The Internet is a great source for decoding trouble codes. Sites like obd-codes.com allow you to search for the code and tell you which component is faulty. You can also use a search engine. Type the trouble code (it will be in the form of a "P," followed by a four-digit number) and the specific make, model and year of your vehicle. This will compile a list of forum postings from people who have had the same trouble code as you. They will usually offer some suggestions for fixing the problem. If you still can't decode your trouble code, contact a Ford dealer. He will be able to tell you which component is faulty.
Clearing a Trouble Code
Once you have fixed the emissions component that caused the check engine light to illuminate, use the diagnostic scanner to clear the code from the computer. Plug the diagnostic scanner into the diagnostic port on your Expedition. Turn the key to the run position. Use the scanner to read the codes. Once the scanner is finished, press the button to clear the trouble code. Remember that clearing the trouble code will not solve the underlying malfunction by itself. If you clear the trouble code without fixing the malfunctioning emissions component, the check engine light will illuminate again within a few miles.