Engine light on after replacing Fuel Pump

I just had a new fuel pump put in my 98 Chevy Lumina LTZ. The next day the engine light came on. Took it back to mechanic and of course he said it was the gas cap. Two days later, light was on again. Took it back to mechanic, again he says it must be the gas cap. There is also a faint smell of gas inside the car, it was much stronger right after the replacement but it's still there. Can I get some suggestion of what to check other than the gas cap, please.

TY

Chances are real good the seal is leaking in and around the fuel pump, or the seal to the filler tube is not sealing.....or the vent tube has been stretched...any number of things may have gone wrong.

The code was not there prior to FP replacement, it is there now, so the mechanic messed something up in his installation and he is now responsible to find it and fix it. Pretty simple. It is in cases like these that you learn what kind of people you are dealing with. Anyone can make an honest mistake, admitting to it is where the integrity lies.