Ford 2003 Mustang Workshop Manual page 3

Positions 5 through 7 indicate vehicle line, series and body type.
P40 — Two-door coupe
P42 — Two-door coupe, GT (Mach One available in GT Coupe only)
P44 — Two-door convertible
P45 — Two-door convertible, GT
P48 — Two-door coupe, Cobra
P49 — Two-door convertible, Cobra
Engine Code
The eighth VIN position is the engine displacement and number of cylinders code.
4 — 3.8L, OHV, EFI, six cylinder
R — 4.6L, DOHC, EFI, eight cylinder (Mach One)
X — 4.6L, SOHC, EFI, eight cylinder
Y— 4.6L, DOHC, S/C, EFI, eight cylinder (Cobra)
Computer Generated Check Digit