2007 ES 350 136,000 miles

June 2018 - CEL --> :Low air tire light --> Red ! --> Check VSC all came on. Brought to dealer. They say Ignition colt #3 .problem solved so it's clear the on-board diagnostic warnings work correctly (in June 2018 anyway)
December 14, 2018 - CEL --> Low air tire light --> Red ! --> Check VSC all came on at 8 pm. brought to the same dealer. They say (after $165 diagnostic charge) their computer read P2401 and I need to replace the Carbon Vapor canister ($165/ hr labor x 3.8 hours + parts = $1419).

They said it's emission related and is not urgent to replace. I however know that if there are any other issues I will not be notified of them because the lights are already "on" on the dashboard. So I set up to get the job done this morning (Mon. 12-17) but when I left work yesterday at 8 am the lights were all off (135 miles since Dealer read code P2401). I have driven about 160 miles since the lights first came on and about 30 since they went off yesterday morning. Anyone here know of or heard of this? Can these advanced on-board electronics somehow diagnose and correct something (Carbon canister failure) ? Was there a fuel vapor build up? Thanks for any feedback!

NOTE: the night before I started the car and the lights all came on last week the car was parked on a slope with the front bumper angled downward. Did this affect the read (or false read) of the Carbon Vapor canister fault?

EDIT 6:35 pm - 243 miles since lights first came on. 47 miles since lights went out (Sunday 8 am) . I think it was like 25-30 degrees when lights came on last week. It's been mid 30's and the 40's this week. Does the cold temperature have any effect on this? BUT it was warm in the dealer when they read the code (yes, lights were on when I brought car to dealer last Friday). And, again, the night before I started the car and the lights all came on last week the car was parked on a slope with the front bumper angled downward.