Possible causes

– Missing or loose fuel cap
– Incorrect fuel filler cap used
– Fuel filler cap remains open or fails to close
– Foreign matter caught in fuel filler cap
– Evaporative Emission (EVAP) canister or fuel tank leaks
– Evaporative Emission (EVAP) system hose leaking
– Fuel tank leaking

Tech notes

The fuel tank filler cap and the Purge Volume Control Valve are the more common problems that will trigger the P0456 code on Nissan vehicles.

There is factory Nissan service bulletin to help diagnose the P0456 code:
Nissan Factory Service Bulletin OBDII Code P0456

Nissan models with factory service bulletin:

2005-2007 Nissan Pathfinder
2005-2007 Nissan Pathfinder Service Bulletin OBDII Code P0456

2007-2009 Nissan Altima Sedan
2008-2009 Nissan Altima Coupe
2007-2009 Nissan Altima Hybrid
2009 Nissan Maxima
Nissan Factory Service Bulletin OBDII Code P0456

When is the code detected?

Malfunction is detected when Evaporative Emission (EVAP) control system has a very small leak, EVAP control system does not operate properly.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Possible a noticeable fuel odor caused by the release of fuel vapors

P0456 NISSAN Description

This diagnosis detects leaks in the Evaporative Emission System (EVAP) purge line using engine intake manifold vacuum. If pressure does not increase, the Engine Control Module (ECM) will check for leaks in the line between the fuel tank and EVAP canister purge volume control solenoid valve under the following vacuum test condition.
The vacuum cut valve bypass valve is opened to clear the line between the fuel tank and the EVAP canister purge volume control solenoid valve. The EVAP canister vent control valve will then be closed to shut the EVAP purge line off. The EVAP canister purge volume control solenoid valve is opened to depressurize the EVAP purge line using intake manifold vacuum. After this depressurization is implemented, the EVAP canister purge volume control solenoid valve will be closed.

http://cardiytool.com/images/3022.gif

NISSAN Technical Service Bulletins for P0456 code