The Error Codes for Loose Gas Cap & Gas Tank Seal

by Chris Brake
itstillruns article image
pumping gas image by Mat Hayward from

Almost every car owner that has ever filled up a gas tank has encountered a “Check Engine” light that comes on when the gas cap has not been closed properly. This warning light can indicate a wide range of problems, some minor and others much more serious; however, if the light comes on right after filling up, it probably indicates that the gas cap is loose.

Diagnostic Codes

It is never a good idea simply to assume that the "Check Engine" light is on because the gas cap is loose. Therefore, this warning light should be properly diagnosed to pinpoint the exact problem. Most owners will take their car to a repair shop and have it hooked up to an expensive system that will diagnose the problem. However, if you happen to be short of cash, there's a simple way for you to troubleshoot this problem. Most late-model cars come with a computerized system that provides diagnostic information. Manufacturers such as Autel produce consumer hand-held diagnostic devices that can be hooked up to a car's computer terminal for a quick diagnosis. As of 2010, these hand-held devices can be purchased for as little as $20.

Common Codes

One common error code that you may encounter is “P0440” which indicates a loose gas cap. However, this is not the only code involving the fuel tank that could set off the “Check Engine” light. Many cars will also generate a warning signal if the on-board computer detects any fuel vapor escaping from the gas tank. These codes typically will be in the “P0400” series and could indicate something more serious than a loose gas cap, such as a broken seal or even a leak in the gas tank, which is a much more serous problem.

Reset Engine Light

You will want to know how to reset the “Check Engine” light once the problem has been diagnosed and repaired. The method for resetting the light varies from one vehicle to another, but on many cars, a simple technique can be used. This method requires that you access the car’s fuse box; you will probably need access to the car’s service manual as well to locate the fuse box and identify the engine light fuse. Once you’ve located this fuse, simply remove it with a pair of pliers, wait ten seconds and then reinsert the fuse.

More Articles

article divider