Here are a few possibilities:
* A pre-existing, intermittent problem: The problem causing the light to illuminate might have been present *before* the test, but intermittent enough that it didn't trigger the light until after. The driving conditions during or immediately after the test might have triggered the issue. Think a sensor that's working erratically, or a minor leak that worsened with the car's movement.
* A new, unrelated problem: Something truly did go wrong *during* or *immediately after* the test, such as a loose connection somewhere in the system, a sensor failing under stress, or even something unrelated to the emissions system (like a minor electrical fault).
* A problem with the OBD system itself: Though less likely, there could be a fault within the vehicle's OBD system itself.
What to do:
1. Don't ignore it: The SES light indicates a problem that needs attention. Driving with a malfunctioning system could lead to further damage or reduced fuel economy.
2. Get the code read: You need to get the Diagnostic Trouble Code (DTC) read from your vehicle's OBD-II system. Auto parts stores often offer this service for free. The code will give a much clearer indication of the specific problem.
3. Address the problem: Once you have the code, you can research the likely cause and determine whether you can fix it yourself or need professional help. A simple fix might be a loose gas cap, but it could also be something more serious.
In short, the timing is coincidental. The emissions test didn't cause the light; a problem within the vehicle did, either pre-existing or newly developed. Getting the code read is the crucial next step.
