The transfer case control module runs the four-wheel drive (4WD) drivetrain and controls the process of shifting gears when the vehicle operates in 4WD mode.The transfer case control module manages engine torque distribution between the drive axles and how much force each axle and wheel gets.A bad transfer case control module can cause engine hesitation, fluid leak in the transfer case, gear shifting issues, and a malfunctioning 4WD mode, among other issues.