2000 Chevy Silverado gas tank vaccum relief valve

Disregard the vacuum relief valve and inspect and test Canister Purge Control Solenoid

The Canister Purge Control Solenoid (CPCS) allows fuel vapor to flow from carbon canister to the engine. Solenoid is normally closed and is pulse-width modulated by the PCM to precisely control vapor flow. PCM controls flow of fuel vapors based on coolant temperature. At temperatures greater than 113 °F (45 °C), purge control solenoid is open. Purge control solenoid is also opened if PCM detects extreme lean air/fuel mixture ratio conditions.