i have a 94 gt and i keep getting dtc 556(Primary Fuel Pump circuit failure), my CEL hasn't turned on. so far i already replaced injectors with 30lb, i replaced fuel pump with a 255, i changed the fuel pressure regulator and i replaced the module next to coolant resevoir. the code was present before changing all these items and i did clear the codes..... does anyone have an idea of what can cause this code....... by the way, after clearing codes, it takes a very long time for the code to re-appear....