Here are some possibilities:
* Faulty Oxygen Sensor: A malfunctioning oxygen sensor can impact fuel efficiency and emissions, triggering the light.
* Mass Airflow Sensor (MAF) Issue: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause inaccurate fuel delivery, leading to the light.
* Crank Position Sensor: This sensor tells the computer the position of the crankshaft. A faulty one can cause misfires or starting problems.
* Throttle Position Sensor: Similar to the MAF sensor, a problem here can affect fuel delivery.
* Evaporative Emission System (EVAP) Leak: A leak in the system that controls fuel vapors can trigger the light.
* Other Sensor Problems: Many other sensors contribute to engine operation. A failure in any of these can trigger the light.
* Loose or Damaged Gas Cap: While seemingly unrelated, a loose or damaged gas cap can cause a small leak and trigger the light. Try tightening it first as this is an easy fix.
* Spark Plug/Ignition Coil Problems: Misfires due to worn spark plugs or faulty ignition coils are common causes.
* Catalyst Converter Issues: A failing catalytic converter can trigger this light.
What to do:
1. Get the codes read: The most important step is to use an OBD-II scanner to read the diagnostic trouble codes (DTCs). Auto parts stores often offer free code reading services. The codes will give you a much clearer indication of the problem.
2. Don't ignore the light: Driving with a persistent "Service Engine Soon" light could lead to further engine damage.
3. Professional diagnosis: Once you have the codes, you can research them online or take your Expedition to a mechanic for diagnosis and repair. Trying to fix things without knowing the problem could be expensive and ineffective.
Simply adding oil won't fix an underlying engine problem. Focus on getting the diagnostic codes read to find the root cause.
