Cucucachu

Check Engine Light accompanied by P0456 - Very Small Evap System Leak and no other codes:
There are quite a few posts about this in the C-class thread. I understand it is about how quickly pressure bleeds from the fuel tank. OBD II runs a test when tank decreases to 75% to 25% full. If it bleeds down too fast, code P0456 or P0455 is triggered.

P0456 Code - minor pressure bleed down from the fuel tank.
P0455 Code - major pressure bleed down from the fuel tank.

I read probable causes like: Fuel Cap, Emission Control Canister Solenoid, Vapor Canister Purge Valve, leaking vent line.

Troubleshooting so far:

I erased the P0456 code. Ck Eng Light extinguished.
Next time I filled the fuel tank, the Ck Eng Light illuminated again when down to 3/4 full. P0456 code returned.

Replaced the Fuel Cap with OEM Cap. Exact matching P/N.
I erased the P0456 code. Ck Eng Light extinguished.
Next time I filled the fuel tank, the Ck Eng Light illuminated again when down to 3/4 full. P0456 code returned.

Any one have solenoid or purge valve failures?

Plutoe

Yep, you do!!