Reasons for HOT TRACTION MOTOR TEMPERATURE in HHP loco

HOT TRACTION MOTOR TEMPERATURE 
a) DEFECTIVE TEMPERATURE SENSOR 
b) DEFECTIVE TRACTION MOTOR 
c) HEAVY TRAIN LOAD AND GRADIENT 
d) HIGH AMBIENT TEMP 
e) GEARCASE OIL DRAINED 
f) LOCO WORKING WITH SINGLE TRUCK