Why did the check engine light come on recently in your 2002 Avalon with 38000 miles and no apparent problems at all?

often the "check engine" light will come on with no apparent problems in any car. there is an array of sensors, actuators, valves, and wiring that is monitored by a computer in the car. if the computer "sees" something that doesnt match a predetermined parameter, it will turn the light on. for example, if your gas cap was left loose, after certain driving conditions are met, the computer notices that there isn't any pressure in the gas tank. Federal Laws say at this point, there should be pressure there. so the computer turns the light on. there would be no problems with the engine itself, just the emission system, but it turns the "check engine" light on to warn you that your car car is no longer meeting federal standards for emissions.

Sometimes there is a false warning light.

To Check:Turn off all accessories and have the key out of the ignition. Disconnect the negative battery connection for about 30 seconds and then reconnect. This action resets the computer and may make the light go out if it was a false alarm. If the light comes back on, then it is possible that you have an actual problem.