Circuit Description

The DTC P0442 Evaporative Emission (EVAP) System Leak Detected diagnostic monitors the operation of the EVAP system. The EVAP control system leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring vacuum decay. The Powertrain Control Module (PCM) monitors the vacuum level via the fuel tank pressure sensor input. The PCM turns ON the EVAP canister purge valve and the EVAP vent valve, allowing the 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 P0442 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 (FTP) sensor
• Fuel pipes and hoses
• Vapor lines
• Fuel filler cap
• Fuel tank pressure control valve EVAP canister
• EVAP canister
• Purge lines
• EVAP canister purge valve