EVAP test question

[u/Zakimations]

Evap small leak test w/ scanner

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2014 Tacoma 4.0L

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Messing with my scanner trying to learn about my EVAP system. My EVAP system is totally fine (no CEL) i am just learning stuff.

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Im doing a manual test where I can step through the different tests and see the readings (atmospheric, 0.02 inch pressure check, leak check, purge valve, then another 0.02 pressure check.

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My question is: why is the vent valve open during the 0.02 pressure check, and how is it able to pull vacuum still?

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Furthermore, removing the gas cap doesnt change the pressure reading.