Theory Of Operation
| EVAP SYSTEM COMPONENTS | |
|---|---|
| CALLOUT | DESCRIPTION |
| 1 | Filter |
| 2 | ESIM Switch |
| 3 | Evaporative Canister |
| 4 | Fuel Tank Vent (Check Valve) |
| 5 | Control Valve |
| 6 | Inlet Check Valve |
| 7 | Fuel Tank Pressure Sensor |
| 8 | To Purge System |
| 9 | Fuel Fill Tube |
This diagnostic tests the evaporative emission (EVAP) system for a small leak when the ignition is turned OFF and the correct conditions are met. Heat is transferred from operating the vehicle and ambient conditions into a vehicle fuel tank during normal operation. When the ignition is turned OFF and the EVAP system is sealed, a change in the fuel tank vapor temperature occurs, which results in corresponding pressure changes in the fuel tank vapor space. This change is monitored by the Powertrain Control Module (PCM) using the fuel tank pressure sensor input. The PCM then makes a judgment on the integrity of the system. With a 0.51 mm (0.02 in) leak in the system, the amount of pressure change observed is significantly less than that of a sealed system.