Evaporative Emission Large Leak Test

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This diagnostic test creates a vacuum condition in the Evaporative Emission system. When the enabling criteria has been met, the ECM commands the normally open Q13 Evaporative Emission Canister Vent Solenoid Valve On/closed and the Q12 Evaporative Emission Purge Solenoid Valve On/Open, creating a vacuum in the Evaporative Emission system. The ECM then monitors the B150 Fuel Tank Pressure Sens or voltage to verify that the system is able to reach a predetermined level of vacuum within a set amount of time. Failure to achieve the expected level of vacuum indicates the presence of a large leak in the Evaporative Emission system, a restriction in the purge path or a malfunctioning Q12 Evaporative Emission Purge Solenoid Valve. The ECM will set a DTC if it detects a lower than expected vacuum level under these test conditions.