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 this test, PCM monitors fuel tank pressure sensor for an atmospheric pressure reading when all DTC parameters have been met with engine running. PCM will then command the EVAP vent solenoid on (closed) and the EVAP purge solenoid on (open). PCM will allow pressure drop in fuel tank for a certain length of time after which it will turn off the EVAP purge solenoid. DTC will set when a certain vacuum in fuel tank could not be achieved due to a large leak.

The following are possible conditions that can result in a large leak detection:

• EVAP vent solenoid is commanded on (closed).
• EVAP purge solenoid is commanded on (open).
• Engine run time greater than 2 seconds.
• Fuel tank level between 15-85 percent full.
• BARO greater than 81 kPa.
• 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.