Das \ am Ende mach die Zeile zwar leserlich kürzer, allerdings fügt der Compiler das wieder zusammen, was die Zeile wieder für den Compiler zu lang macht.
Daher musst du den String splitten:
format(query, sizeof(query), "UPDATE `FracVehicles` SET `fVehid`='%s', `fPosX`='%f', `fPosY`='%f', `fPosZ`='%f', `fPosA`='%f', `fCol1`='%d', `fCol2`='%d', `fFaction1`='%d' ",
FactionCars[i][fVehid], FactionCars[i][fPos][0], FactionCars[i][fPos][1], FactionCars[i][fPos][2],
FactionCars[i][fPos][3], FactionCars[i][fCol][0], FactionCars[i][fCol][1],FactionCars[i][fFaction][0]);
format(query, sizeof(query), "%s, `fFaction2`='%d', `fFaction3`='%d', `fFaction4`='%d', `fFaction5`='%d', `fSpoiler`='%d', `fHood`='%d', `fRoof`='%d', `fSideskirt`='%s', `fLamps`='%d', `fNitro`='%d' ", string,
FactionCars[i][fFaction][1], FactionCars[i][fFaction][2], FactionCars[i][fFaction][3], FactionCars[i][fFaction][4], FactionCars[i][fTuning][0],
FactionCars[i][fTuning][1], FactionCars[i][fTuning][2], FactionCars[i][fTuning][3], FactionCars[i][fTuning][4], FactionCars[i][fTuning][5]);
format(query, sizeof(query), "%s, `fExhaust`='%d', `fWheel`='%d', `fStereo`='%d', `fHydraulics`='%d', `fFrontBumper`='%d', `fVent1`='%d', `fRearBumper`='%d', `fVent2`='%s', `fPaintjob`='%d', `fPrice`='%d' ", string,
FactionCars[i][fTuning][6], FactionCars[i][fTuning][7], FactionCars[i][fTuning][8], FactionCars[i][fTuning][9], FactionCars[i][fTuning][10],
FactionCars[i][fTuning][11], FactionCars[i][fTuning][12], FactionCars[i][fTuning][13], FactionCars[i][fTuning][14], FactionCars[i][fPrice]);
format(query, sizeof(query), "%s, `fTankart`='%d', `fGesperrt`='%d', `fMotorschaden`='%d', `fSperrpreis`='%d' ", string,
FactionCars[i][fTankart], FactionCars[i][fGesperrt], FactionCars[i][fMotorschaden], FactionCars[i][fSperrpreis]);
format(query, sizeof(query), "%s WHERE `id` = '%d'", string, i);
Alternativ kannst du auch jede Variable in ein extra format schreiben und zusammenfügen, anstatt wie hier immer ein paar. Macht es eventuell leserlicher.
Also so:
format(query, sizeof(query), "UPDATE `FracVehicles` SET ");
format(query, sizeof(query), "%s`fVehid`='%s', ", string, FactionCars[i][fVehid]);
format(query, sizeof(query), "%s`fPosX`='%f', ", string, FactionCars[i][fPos][0]);
format(query, sizeof(query), "%s`fPosY`='%f', ", string, FactionCars[i][fPos][1]);
//...
format(query, sizeof(query), "%s`fSperrpreis`='%d' ", string, FactionCars[i][fSperrpreis]);
format(query, sizeof(query), "%s WHERE `id` = '%d'", string, i);