Rep Power: 0

This 01 Civic, unknown trim level, has the P1456 code
www.autocodes.com says:

Missing Fuel cap
Incorrect fuel filler cap used
Fuel filler cap remains open or fails to close
Foreign matter caught in fuel filler cap
EVAP purge control solenoid
EVAP canister
Fuel tank pressure sensor

When we purchased the vehicle, there was no fuel cap. I installed an OEM fuel cap and cleaned and inspected the filler neck for dents or debris; none found. The code still comes back after a few drive cycles and, over the past four months or so, the code has been erased probably 15 times. While I don't drive the vehicle myself often, I've told my wife that the cap needs to be closed 'till several clicks are heard, so I have to assume that the cap being left loose isn't the problem.

If autocodes.com is to be believed, that leaves an EVAP purge control solenoid, an EVAP canister or a fuel tank pressure sensor. If experience with other vehicles is anything to go off of, the charcoal canister itself is very unlikely, but who knows?

Is one of these more likely a trouble spot than the other? Is there troubleshooting to figure one part failure out over the other? Should I be looking at any other "Oh, this always happens," type failures like a particularly troublesome hose or connection?

Thanks in advance for any help!

 
Rep Power: 125

A cracked fuel filler neck will also throw that code. That happened when I owned my Integra. It stops the fuel tank from pressurizing so it throws the code and it would usually come on after a fuel cycle. That may be your culprit. There are lots of comprehensive videos online showing the entire process.

 
Rep Power: 98

I'm no expert on Honda's EVAP system, but I believe the P1456 code relates to the tank side of the system. So if the cap isn't the issue and you don't see any problems with the filler neck, then it is most likely one of the plastic/rubber hoses connected to the filler neck...or maybe a faulty fuel pressure sensor (this doesn't seem common).

There are quite a few hoses and check valves and filters to look over on these EVAP systems. If you don't see anything obvious, then it may be quickest to just replace the purge valve as a guess. They aren't particularly expensive ($40-$50) and they're easy enough to replace.

If that doesn't work, then you'll probably have to do a smoke test to find the leak. There is also a very small chance that there's a layer of rust around the ridge of the filler neck where the fuel cap o-ring seals against. A quick check could eliminate that possiblilty (if it is rusty, then clean it with some steel wool (or similar) and some brakleen).

 
Rep Power: 132

A common issue with the EVAP system on these cars is a bad By-pass (Canister) Shut Valve (CVS). It is located attached to the EVAP canister under the car. Many replace the canister at the same time as the valve will likely be rusted on. Mine threw the P1457 code though.