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Fuel Pump

I have a 2005 chevy impala 3.4. I had the fuel pump replaced in the fuel tank. I have had it back 4 times because the check engine light keeps going on. The mechanic says it is carbon in the fuel tank and it takes time . I am so frustrated. Can anyone help me figure out how to rix the problem. Computer codes says it is infact emissions problem.

The mechanic says it is carbon in the fuel tank and it takes time .

I love that one.  The only carbon in the fuel tank is the hydrocarbon molecules that make up the gasoline.  OK I suspect what he may have been suggesting is that the light was indicating a problem with the carbon canister that is part of the vapor recovery (vent) system for the fuel tank. He may be thinking that in time the canister may dry out.  I doubt if that is going to work unless this is all very recient.

Are you in the habit of topping off the tank when you fill it?  You could have caused the problem by doing that.  The owner's manual and stickers on your car in the glove box or in the gas cap area likely warn you about it.  

 In order for anyone here to give the best guess, we need to know the exact code that is stored in your car's computer that explains why that light is on.  Many auto part stores will read the light for free.  It should be in the form [P0123].  If you can get that information and post it in a reply to your message above, it should prove helpful.

It could also be an incorrectly installed vent line or tank hose causing a vacuum leak that would set the DTC for an evap system problem. The evap system tries to keep a vacuum in the tank to insure that gas vapors are not escaping. If there is a leak, it cannot maintain vacuum, and sets a code. The tank would need to be removed again to re-check all that work, and I suspect this mechanic doesn’t want to do that, even though he knows he must. Go back and insist he fix it. The other option is to have another shop fix it, then sue him for the costs.