What does it mean?
When I encounter a code P0456, it means that the powertrain control module (PCM) has detected a malfunction in the evaporative emissions (EVAP) system. The malfunction is due to a small leak and is typically associated with a defective, loose, or missing fuel cap. The EVAP system is designed to capture fuel vapors (from the fuel tank) before they escape into the atmosphere. It utilizes a closed reservoir to store excessive vapors until the engine is prepared to burn them.
Excessive fuel vapors are discharged to the reservoir (usually called a canister), through a specially designed valve and a network of metal tubes and rubber hoses. The pressure that is developed (when fuel is stored) acts a propellant, causing the vapors to vent through the tubes and eventually into the canister. A charcoal element is contained in the canister. It absorbs fuel vapors and holds them for release at the appropriate time.
Major components of the EVAP system include: the charcoal canister, the EVAP pressure sensor, the purge valve/solenoid, the vent control valve/solenoid, and a complex system of metal tubes and rubber hoses that stretches from the fuel tank to the engine compartment. The EVAP system uses engine vacuum to draw fuel vapors into the intake manifold where they can be burned as opposed to being released into the atmosphere. The purge control valve/solenoid is electronically controlled by the PCM.
It regulates intake vacuum to the EVAP canister so that fuel vapors are drawn into the engine only when conditions are ideal for the vapors to be burned most efficiently. The vent control valve/solenoid is also controlled by the PCM. It allows excessive pressure to be released from the EVAP system and fuel tank. When pressure reaches a certain level, the PCM commands the vent control solenoid to open the valve and the excessive pressure is released into the atmosphere.
The EVAP pressure sensor allows the PC to monitor EVAP system/fuel tank pressure. If EVAP and/or fuel tank pressure remains too low over a set period of time, and under certain circumstances, a code P0456 will be stored and the malfunction indicator lamp (MIL) may be illuminated. Since this code specifies a small EVAP system leak, there is likely to be some pressure in the system. If there is no pressure in the system, a large EVAP leak code will likely be exhibited.