check engine light on 2006 Kia Rio

check engine light came on about 100 miles after timing belt, new plugs, new belts, & trans. service. car has 70700 miles. Mechanic says code indicates evaporative canister problem, but, he cleared code and said drive car, as it may have been a fluke. Says if it comes back on, leave car with him so he can futher diagnoise. Any thoughts about that and costs ideas? THANKS

Asked by for the 2006 Kia Rio
The most common cause for evaprotive system faults on just about all newer vehicles is a loose or faulty gas cap. The evap system must be completely sealed when the engine control module performs its evap system test. If the gas cap is loose or worn enough to cause a small fuel vapor leak the check engine light will come on indicating a fault. Sometimes all that is necessary to correct the fault is to secure the gas cap. If the light comes on again after securing the gas cap then the system will need to be diagnosed in order to find the leak. The most common way to inspect the evap system for leaks is to inject smoke into the system using a special tool.