That's wrong and the mechanic should know that. For 96 and newer cars, OBD 2 (onboard diagnostics, second generation) systems are in use, and the codes that come up are four digit codes.

That means that the code you got is 1255, not four individual one-digit codes (even a pre-96 car would have two digit codes, not single digit). Generically, a 1200-series code deals with fuel and air metering, but unfortunately I don't have a listing for a 1255. What symptoms does your car have? Is it just bad gas mileage or is it acting up in other ways? Post up as a reply here with anything along those lines that you can think of and I'm sure we'll figure out the problem.