pulled a code

[Flamed95stang]

ok, my friend has a 94 gt, mith mods as follows: Eibach Sportline 2" springs, Bullitt 17x9 wheels, Mac Cold Air kit, BBK 70MM Throttle Body, Pro-M Remote Optimizer, TrickFlow upper and lower intake, Mac Unequal Length Headers, Mac Prochamber, Bassani Forward exit catback, MSD 6AL Ignition system, 8MM Trickflow wires, 255# BBK Fuel Pump, Adjustable fuel pressure regulator, Mac Underdrive pullies, 4.10 Motorsports gears, white face guages, clear corners, cobra r clutch, Steeda Adjustable & quadrant, autometer air/fuel & water. His check engine light would come on occasionally, he thought no big deal. He put on a afpr and now it stays on constantly, so last night I bring my scanner up to his house and run it for codes, I pulled a 123 (think that was the number) but it was for the tps voltage beyond maximum limit or range or something like that, no big deal. Heres the one im wondering about, code 998 means hard fault present, wtf is a hard fault, in my 7 years or working on mustangs I have never heard of such a thing, any help here would be great.