The p0456 error code is a fairly common cause of the Check Engine Light in a Honda Accord. In this article I walk through how to get rid of a Check Engine Light (CEL) that is the result of a p0456 code – for good!

Eliminate P0456 Error Code in a Honda Accord


First of all, this error code refers to the following:

  • P0456 – Small Leak Detected in Evaporative Emissions System

This means that the ECM (car’s on-board computer) has detected a vapor leak in the evaporation system. The leak is small, smaller than 0.020 inches, but it means that gas vapors are escaping.

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Over the years I have had the P0456 error codes periodically, and the reason has typically been that the gas tank cannot hold a vacuum: it has a leak somewhere. In the vast majority of cases, the leak occurs around the gas cap seal. Either the gas cap is loose (not tightened all the way), the rubber seal in the gas cap is bad or the lip of the gas tank that the gas cap seals against is rusty causing a poor seal.

To make sure it is not a loose gas cap, after every fill-up, turn the gas cap at least 3 clicks. Even with the new OEM gas cap, get in the practice of turning the gas cap at least 3 clicks.

The easiest way to deal with this problem is to buy a new gas cap, but the dealership will charge around $95 for a new one. You can buy a replacement gas cap from Amazon fairly inexpensively:

Gas Cap for a Honda Accord 2004

Other Causes

If the gas cap has a nice tight fit, and you are sure it is not leaking, here are a few less-common reasons for the P0456 error code.

  • A small hole or leak in the fuel filler hose
  • Fuel pump mounting flange gasket leak
  • A leak in the top of the gas tank
  • Defective fuel-tank pressure sensor
  • Rusty or corroded gas tank lip


The seals on gas caps tend to go bad after 5-10 years it seems. When I replaced my gas cap, the check engine light (CEL) went off (note, unless you reset the light with an inexpensive OBDII meter, you will have to wait for about 1 tank fill-up before the CEL will turn off).

Thanks for reading, and I hope you found this helpful!