Circuit Description

The DTC P0456 Evaporative Emission (EVAP) System Very Small Leak Detected diagnostic monitors the operation of the EVAP system for leaks as small as 0.020 inch (0.5 mm). The EVAP control system leak detection diagnostic strategy is based on applying vacuum to EVAP system and monitoring vacuum decay. The Powertrain Control Module (PCM) monitors vacuum level via the fuel tank pressure sensor input. The PCM turns ON the EVAP canister purge valve and the EVAP vent valve, allowing engine manifold pressure to draw a small vacuum on the entire EVAP system. If sufficient vacuum cannot be sustained over a given period of time, a small leak or a malfunction is suspected and DTC P0456 sets. The EVAP system used with this powertrain is part of an On-Board Refueling Vapor Recovery (ORVR) fuel system.

The EVAP system as defined by federal regulation includes the following components: fuel tank, EVAP canister vent valve, fuel tank pressure sensor, fuel pipes and hoses, vapor lines, fuel filler cap, fuel tank pressure control valve, EVAP canister, purge lines and EVAP canister purge valve.