'06 PT setting CEL-gascap

Bought this thing a month ago. It started setting the CEL when the tank was almost empty. Took it in to Otterzone and it scanned as gas cap. Put a new cap on and it is still doing it. Clear the code and it stays off until it is below 1/4 tank. Any ideas/known issues?

Thanks!

I believe there is a little air pump that pressurizes the tank and measures the leakage. There would be a rubber hose between this pump and the tank. Maybe your problem is there. Or else it's in the evaporative emission control line to the charcoal canister, if they use those any more.

R.

https://m.youtube.com/watch?v=Dl9Bi_kuWkY

Don’t know if this will help, but you may get an idea on what to check. Might save you some shop rates....