Is your Check Engine Light on? Are you getting a P0456 error code from an OBDII reader in your vehicle? This article addresses some of the most common causes of this error, and more importantly, how to fix them!

Okay, so you diagnosed your check engine light with an OBDII reader and found out that you have error p0456. Now what?

What Does P0456 Mean?

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.

Over the years I have had the following error code periodically: P0456, 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 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.

The easiest way to deal with this problem is to buy a new gas cap, but the dealership will charge around $65 for a new one. You can get the OEM replacement (part# 77300-33070) for 1/4th the price on Amazon here, or, if you can live without the tether, even less at 1/10th the price here.

One thing to confirm is whether you have a threaded gas cap or a studded cap. I had the threaded cap, so that is the cap I ended up getting.

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).

The other problem can be a rusty or corroded gas tank lip, so that even if you have a new gas cap, it still can’t make a nice seal. In this case, it is just a matter of cleaning the rust off. I also had that problem recently.

The tools required:

Step by Step Procedure to Fix a P0456 Error

Here is the procedure I followed to fix that.

01-gas-cap-cleaning-supplies

Here is the OBDII reader. Here it is displaying the P0456 code. If you have one of these units, reset the Check Engine Light after you do this repair, to see if the error code comes back.

This is the ‘before’ photo of the gas cap. Clearly it needs some cleaning…!

03-rusty-gas-cap

Even before you remove the gas cap, take your vacuum cleaner and suck up the sand, grit, and dust. We don’t want that to get into the gas tank.

04-vacuum-gas-cap-area

Here is the gas cap before cleaning.

05-gas-cap-not-clean

Here is the lip of the gas tank. Notice the rust and corrosion around the rim.

06-rusty-gas-port-before

We are going to be filing off the rust, so to prevent the particles from getting into the gas tank, stuff a rag in there.

07-put-in-rag

Here is an especially bad spot of rust, very likely the source of the leak…

08-scrape-off-rust

Use a file to scrape off the rust.

09-scrape-off-rust

Once it is cleaned off, put a little rust inhibitor on there, for example, I used this silicone spray.

10-spray-silicone-on-rag

Wipe off the rust you have filed off, and apply the silicone to the rim.

11-wipe-off-gas-tank-lip

Also clean the rubber seal on the gas cap.

12-wipe-off-gas-cap-seal

This is a photo after everything has been cleaned.

13-cleaned-gas-cap-and-lip

Replace the gas cap.

14-cleaned-gas-cap

After driving for ~ 500 miles, the P0456 error code has not returned!

If you determine that your gas cap is bad and needs to be replaced, here are links to the correct parts on Amazon:

Thanks for reading, and I hope this was helpful!

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