Here's the breakdown:
1. Diagnose the Problem: Before doing anything, you *must* find out why the light came on. This is crucial. You can:
* OBD-II Scanner: This is the best method. A relatively inexpensive OBD-II scanner (available at most auto parts stores) will read the Diagnostic Trouble Codes (DTCs) stored by your Expedition's computer. These codes will give you a clue about what's wrong. Look up the codes online (many free resources are available) to understand their meaning.
* Auto Parts Store Check: Many auto parts stores will scan your vehicle for free. They can tell you the code(s) and might even give you advice on the potential fix.
2. Repair the Problem: Once you know what's causing the light, fix it! This could be anything from a loose gas cap to a more serious issue requiring professional repair.
3. Resetting the Light (After Repair): Once the problem is fixed, you can reset the SES light. There are a few ways to do this:
* Disconnect the Battery: This is the simplest method, but it's not always reliable. Disconnect the negative (-) battery terminal for about 10-15 minutes. Reconnect the terminal and start the engine. The light *might* go off after a few driving cycles.
* OBD-II Scanner: Most OBD-II scanners have a "clear codes" or "reset codes" function. This is the most reliable method, as it clears the codes from the computer's memory directly.
* Key Cycle Method (Less Reliable): Some vehicles allow for a key cycle reset. This generally involves turning the key to the "on" position (without starting the engine), waiting for a certain time, then turning it off and repeating several times. This method is unreliable on many modern vehicles, including the 1999 Expedition; it is unlikely to work and shouldn't be the first method tried.
Important Considerations:
* Driving Cycles: After resetting the light, drive your Expedition for several driving cycles (meaning several start-stop cycles) to allow the computer to monitor the system and confirm that the problem is resolved. If the problem persists, the light will come back on.
* Professional Mechanic: If you're not comfortable diagnosing and fixing the problem yourself, take your Expedition to a qualified mechanic. They have the tools and expertise to properly diagnose and repair the issue. Ignoring the SES light could lead to more significant and costly problems down the road.
Ignoring the "Service Engine Soon" light is not a good idea. It indicates a problem that needs attention to prevent further damage or potential safety hazards. Diagnose, repair, then reset.
