Gas cap light came on after replacing with a new one

Unless the gasket in the cap is bad and does not make a good seal there is no need to replace it when the gas cap light comes on, it is usually a cap that has not been screwed in correctly. Have you tried to unscrew the cap and put it back on, slowly? Perhaps the code is still in the computer's memory and all that is necessary is to reset the computer. Ask your mechanic if he performed a reset after installing the new cap, even if the light went off.

Gas cap is not the only thing that will set a check engine light. What was the code??

I am not sure what the code was as they reset the computer after installing the new gas cap. The light went off and came back on the next day when the car was started. Could this be a faulty gas cap?

So, if the light came back read the code again, and write it down!

NEED THE CODE.

PO455

Code indicates fuel EVAP system leak: Missing or loose fuel cap. Incorrect fuel filler cap used. Fuel filler cap remains open or fails to close. EVAP canister or fuel tank leaks. EVAP system hose leaking. Fuel tank leaking. I would go back to the mechanic, let him remove the gas cap, inspect it well and replace it, then clear the code again, if it comes back then you may also have one of the other conditions.

V.W. Had a issue with the purge valve hanging up.

What ended up being the problem after all my Passat it doing the same thing right now the gas cap seems pretty good don't see no issues with my check engine light comes on n the gas cap light also here n there I'm getting the same code P0422

Same I’m getting p0422

Me too my light will come in then go right back off then two days later my check engine light comes on. I replaced my gas cap and they rest my code

I have same issue with 2001 passat 2.8l v6. Brand new oem gas cap bought and installed. Still get check engine light p0422 code. Can't see any fuel drips or smell gas leaks but light keeps coming on with same code. Could it be a vacuum leak?