The problem could range from something minor (like a loose gas cap) to something serious (like a failing catalytic converter). To find out the specific issue, you need to:
* Have the code read: You can use a relatively inexpensive OBD-II code reader (available at most auto parts stores) to retrieve the diagnostic trouble code (DTC). This code will give you a clue as to the nature of the problem.
* Take it to a mechanic: A mechanic can read the code, diagnose the problem, and provide a repair estimate.
Ignoring the SES light is not recommended. Driving with a problem could lead to further damage to your engine or other components, potentially leading to more expensive repairs down the line.
