Toyota Repair: Check engine light, service reminder, gas mileage

Question
I refueled my car a couple of days ago, and added fuel injector cleaner.  I have a 98 Avalon, 104,000 miles.  The check engine light came on shortly afterwards.  I have checked the gas cap--it is and was on securely.  The gas mileage seems to be lower than normal, but no other apparent problems.  Is this one of those automatic indicators that come on at predetermined miles?

Answer
The 98 Avalon doesn't have service reminder lights and the check engine light will only come on if the computer detects a malfunction that can affect emmision control systems, I recommend that you have a repair shop or the Toyota dealer hook up the diagnostic scantool and see what the code is that triggered the check engine light, if you like, you can contact me after you know what the codes are and I may be able to offer some advice on how to repair the problem.