System Description

This diagnostic test the Evaporative Emission (EVAP) System for a small leak, when the key is turned OFF and the correct conditions are met.

Heat from the Exhaust System is transferred into a vehicle fuel tank while the vehicle is operating. When the vehicle is turned off a change in fuel tank vapor temperature occurs. With the EVAP System sealed, this results in corresponding pressure changes in the fuel tank vapor space. This change is monitored by the control module using the fuel tank pressure sensor input. The control module then makes a judgement on the integrity of the system. With a 0.51 millimeter (0.02 inch) leak in the system, the amount of pressure change observed is significantly less than that of a sealed system.

If the control module detects a pressure change less than a calibrated amount, DTC P0442 sets.

The following table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP canister purge and vent solenoid valves.