The evap system has to have a vent. It is there to allow air to escape while fueling and also keeps the tank from imploding while using fuel.
When the PCM does its own internal test to be sure the system has no leaks, it will close off the vented hose by a solenoid and test the system.
As far as the capped line, the canister may fit several different applications that use the nipple.
Do you have any codes or issues with the system?
Images (Click to enlarge)
Friday, January 11th, 2019 AT 5:30 AM