What does the code P0456 mean on a 2004 Ford Taurus?

So my car’s emission systems light came on last Saturday and after work today I took it to the local Auto Zone to have an onboard diagnostic done to see what the code was, as some friends had recommended. I have a 2004 Ford Taurus with about 146,000 miles on it. It came back as only one code, P0456, which according to the clerk meant one of four things.

1.) Defective, loose, or missing fuel cap
2.) EVAP Canister Broke, hose cracked or not connected
3.) Purge or vent solenoid defective
4.) Vaccum leak at engine

I asked him if there was anyway to eliminate a few of these, but he wasn’t sure and said I would have to take it to a dealer or a repair shop (which I expected). I was wondering if anyone had any tips or tricks so I can eliminate a couple of these, and also if this is a five alarm fire I should be panicking about. I did call my Dad and he did not seem overly concerned about it. Plus my car is still running fine and the light has remained steady and not flashing. My friend at work suggested I put a piece of black electrical tape over it and ignore it, but I want to be sure it passes inspection in September.


P0456 means you have a 0.020" size evap leak.

My recommendation:

Go to a shop
They need to connect their evap/smoke machine to determine the location of the leak

If you don’t want to pay for diagnosis or labor, you’ll have to pay for parts which you’ll install yourself and hope for the best.

If you want to go this route, DO NOT clear the fault code after replacing your chosen component(s)

If everything is fine, the check engine light will eventually turn off and stay off.

If you want to guess, replace the fuel filler cap and the evap purge valve. Those are two relatively inexpensive components which often cause evap leak codes. If the fuel filler cap seal is rotten, you’ve most likely found the problem

Of course, there are numerous other problems that could cause P0456

Leaking fuel filler hose/neck
Leaking fuel tank sender seal

These other things are much more difficult to replace/repair, though

I gave you two options. Up to you which way to go.

The code indicates that there’s a very small leak in the EVAP system. This could be caused from a defective gas cap.

Try this. Remove the gas cap and apply a thin coat of petroleum jelly to the seal on the gas cap and reinstall it. Make sure the gas cap clicks a few times. Now drive the vehicle and see if the Check Engine light turns off. If it does, it usually means the gas cap requires replacement.