The most common cause of a Honda check engine light being on is a DTC P1456, and it's usually caused by a loose or missing gas cap (usually). This isn't the only reason though, the code or DTC P1456 is caused by a leak on the tank side of the evaporative system, and the most common cause is a loose or missing gas cap, but it could also mean a leak in the fuel tank, or one of the tubes or hoses.
What to do if the Check Engine
Light Comes on after Refueling
So if your Honda check engine light comes on after refueling your vehicle, the first thing you should check is the gas cap, check to see if it's missing, If it's not missing, make sure the cap is tight by making sure it clicks three times after it has stopped turning. Once you have checked the condition of the gas cap, the vehicle has to run through two driving cycles and two complete test on the evaporative system before the light will go out on its own. If the vehicle passes both tests, the check engine light will go off and the DTC P1456 will be cleared until the next fault occurs.
Evaporative System Tests and Drive Cycles
A drive cycle is when the engine is stone cold and then its run until it reaches operating temperature; this is considered one driving cycle. During the drive cycle, the vehicle computer will perform a test on the evaporative system. The computer will pull a vacuum on the fuel tank and then monitor the voltage at the fuel tank pressure sensor, if the tank loses vacuum during the test, the computer senses the leak by a voltage drop at the FTP sensor and turns on the check engine light. The evaporative system has to pass two of these tests with no leaks before the vehicle computer will shut off the check engine light. The check engine light can also be cleared manually by using a scan tool, but it's not necessary.
What if the Check Engine Light Never Goes Out?
If your Honda check engine light never goes out, and the gas cap is in place and tight, most likely you have other issues or a faulty gas cap. I recommend finding a automotive shop or dealership who has the equipment to diagnose the problem properly, not just pull a code and guess at the problem. Honda dealers have diagnostic tools to check the evaporative system; these diagnostic tools can actually run the evaporative test with the scan tool without going through the drive cycles.
Having the right mechanic doing the job can save you time and money, having the right tools for the mechanic is key, and most small shops will not spend the money on sophisticated tools. Dealerships have to spend the money because they are forced to, by the manufacturer. The hourly rate at a dealership may be greater than a small shop, but it's because they have the right tools and the proper information to fix your vehicle, but you still need to get the right mechanic.
If you have a question about your check engine light, please don't hesitate to ask in the Facebook comment box or in the other comment box, I answer all questions :)
What's Inside a Honda Canister
Vent Shut Valve
How to Test A Honda Canister Vent Shut Valve
1999 Honda Accord v6 P1457 Code Fix