Good morning - I think we may have all encountered this at some point. I have been trying to diagnose my problem and why this check engine light keeps coming on. I checked the purge valve at he engine and it appears to be working fine. I checked the vent valve back at the charcoal canister and it seems to work as it should. With my scan tool I'm able to turn on and off the purge valve and the vent valve. I put the scan tool on live data and drove down the road. The vent valve showed "venting" all of the time while the purge valve would go from 0% to 100% depending on the speed of travel. My question is when does the vent valve ever close? How long should it stay open? The gas cap may be an issue but the dash message will say "Gas Cap" if it isn't on good and that message hasn't been coming on lately?

Thank you