Small emissions leak making check engine and 4lo light blink?

Good evening, please help! I bought a forerunner a few months ago and two days after purchasing it the check engine light, traction control, and for low light started blinking on my dash. I called the person that sold it to me and of course they acted like they’d never seen it before, but suggested changing the gas cap. I took it into a buddy of mine who ran the codes and when he did the smoke test found a small leak at the charcoal canister, so I paid to have that replaced and two days later the light came back on... Tried the new gas cap and nothing takes it away. I don’t know what else to do. Any help is greatly appreciated.