System Description

The DTC P0442 Evaporative Emission System Leak Detected diagnostic monitors the EVAP system for a small leak. The diagnostic runs when the ignition is in the OFF position and the correct conditions are met. While the vehicle is operating there are sources of heat transferred into the tank from the following:

• Exhaust heat
• Engine heat
• Ambient temperature

When the engine is topped and the ignition is in the OFF position a change in the fuel tank vapor temperature occurs. This results in a change in the pressure of the fuel tank vapor space. This change in pressure is monitored by the control module using the fuel tank pressure (FTP) sensor input. The EVAP diagnostic detects leaks as small as 0.51 mm (0.020 in). If the control module detects a change in the fuel tank vacuum/pressure less than a calibrated amount, this DTC sets.