Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Chevrolet Impala Check Engine Light Due to Gas Cap Issue
Chevrolet Impala Problem
Average Mileage: 91,933 mi (23,000 mi - 160,000 mi)
I kept getting the check engine light and tighten gas cap. Paid dealership (almost $200 including labor) for a new gas cap. Now almost a year later getting same check engine light and tighten gas cap. This time they're saying I need to replace evap vent solenoid for $130. It seems like a lot of the issues with this car are the same. GM should step up and solve them.
Visitor, 2011 Chevrolet Impala, 23,000 mi
3rd time in 7 months the check engine light came on and dealer keeps telling me the gas cap isn't on tight enough. i'm soooo sorry i bought this car!
Engine light comes on, reads large emissions leak, replaced gas cap.
Visitor, 2007 Chevrolet Impala
Check engine light is on. It says check gas cap, However gas cap is tight.
Visitor, 2006 Chevrolet Impala, 114,000 mi
Replaced gas cap; still have problem.
Visitor, 2006 Chevrolet Impala, 110,000 mi
Same issue, worn gas cap allowing air in the tank and check engine light. Bought a new cap and fixed the issue. 50,000 miles later still no re-occurrence.
Visitor, 2011 Chevrolet Impala, 58,000 mi
Same issue, same story, paid for the most expensive gas cap they could find!
Visitor, 2006 Chevrolet Impala, 131,000 mi
had to buy a gas cap from chevy dealership because of tighten gas cap indication
Visitor, 2006 Chevrolet Impala, 97,500 mi
engine light on; replaced gascap...one of many issues with this car...
Visitor, 2008 Chevrolet Impala, 100,000 mi
engine light came one whenever I got gas, replaced cap and it was fine for two years, now it has started again.