Here are the Hertz vehicle classifications:

Class SIPP Car Type
STANDARD
A ECAR Economy(Hyundai Accent)
B CCAR Compact(Ford Escort)
C ICAR Intermediate(Mazda 626)
D SCAR Standard(Ford Mustang)
F FCAR Full-Size(Ford Taurus)
P PCAR Premium(Mercury Grand Marquis)
L LCAR Luxury(Lincoln Town Car)
4WD/AWD
Q CFAR Compact(Subaru Outback)
Q4 IFAR Intermediate(Ford Escape)
L SFAR Standard(Ford Explorer)
T FFAR Full-Size(Ford Expedition)
T6 PFAR Premium(Ford Excursion)
CONVERTIBLES
U STAR Standard(Ford Mustang)
VANS
R MVAR Mini(Ford Windstar)
M4 FVAR Full-Size(Ford Club Wagon)
M PVAR Premium(Ford Super Club Wagon)
M6 LVAR Luxury
SPECIAL
H PXAR Premium(Mercury Grand Marquis)
PRESTIGE COLLECTION
J XSAR Jaguar S-TYPE
J6 XCAR Jaguar X-TYPE
J4 XXAR Jaguar XJ8
H4 LWAR Volvo V70 Wagon
H6 PSAR Volvo S80 Sedan
I6 LXAR Lincoln LS
T4 LFAR Lincoln Navigator
P IJAR Land Rover Discovery

If anyone knows of missing classifications let me know!