Circuit Description

The Evaporative Emission (EVAP) system is used to store fuel vapors to reduce amount of unburned fuel from escaping into atmosphere. PCM monitors the EVAP system for circuit faults in the fuel tank pressure sensor, EVAP purge solenoid and EVAP vent solenoid circuits. PCM also monitors the EVAP system for small and large leaks. During DTC diagnostic, the EVAP purge solenoid is commanded on (open) and EVAP vent solenoid is commanded on (closed) in order to build vacuum. Once vacuum is obtained, EVAP vent solenoid is commanded off and vacuum should decrease rapidly. DTC will set when vacuum decay is too slow, indicating a blocked vent system.

The following are possible conditions indicating a blocked vent system:

• EVAP purge solenoid is commanded on (open).
• EVAP vent solenoid is commanded off (open).
• Engine run time greater than 2 seconds.
• Fuel tank level between 15-85 percent full.
• BARO greater than 81 kPa.
• ECT and IAT at start-up between 41-90°F (5-32°C).
• ECT and IAT within 50°F (10°C).
• No ECT, fuel tank pressure, IAT, MAP or VSS DTCs set.