No car owner wants to see the dreaded "check engine" light appear on the vehicle's instrument cluster, as it could mean a variety of things, many of them costly. However, if your light turns off without being serviced or diagnosed, it could signify a less pricey problem.
If you recently made a trip to the gas station and did not tighten the gas cap all the way after fueling up, air in the gas line can cause a pressure fluctuation and make your check engine light come on and turn off just as quickly. Check the gas cap to see if it is loose, then tighten it. In the future, make sure to listen for an audible click when tightening the cap before pulling off from the pump.
Because the check engine light comes on when the vehicle's on-board diagnostic system receives a misfire code, driving down a rough or rocky road can cause a code to set and thus turn on the light. Once you reach smooth ground again, the light may go back off. Take note of any potentially rough or unusual driving conditions the car is experiencing when the light comes on, and mention this to your mechanic.
For many minor issues such as low fluid levels, the check engine light may go off once the car is turned off and restarted. If this occurs and the light comes back on, the codes can and should still be read by a mechanic or auto parts store representative.
