It receives inputs and then, on the basis of the program, makes decisions to output commands to other components. The ATCM is a computer that works with other computers in the vehicle. If the customer wants the use of 4WD in the rain or on dry pavement they should select the automatic 4WD mode.Īlthough the NV 246 transfer case and subsystems are extremely sophisticated and appear complex, they are more easily understood if you examine the components in regard to their functions and the relationship between their actions. This range applies constant power to both axles and should be used only in snow or ice conditions, off road, but never on dry pavement. When the driver engages the 4WD High function, the encoder motor shifts the transfer case to the 4-high range and applies the clutch pack to split the torque to the propshafts 50/50. If the tires do not match in circumference all around, change the tires before proceeding and measure the new tires for equal size. You must measure tire circumference with a stagger gauge or a tape measure around the center of the tire tread and equalize all tire pressures before doing anything else. It does not matter that the sidewall labels are read the same. A 15-rpm difference in driveshaft speeds is equal to 1⁄16 inch of tire wear. Many complaints and trouble codes will be set because of mismatched tire sizes or pressures. Tire size is critical to proper performance and operation. This is a very critical issue overlooked by most technicians when they begin a diagnostic routine on this type of transfer case. If the ATCM detects a difference of 15 rpm or more between the propshafts, the ATCM will increase the duty cycle of the clutch pack to send maximum torque to the front axle and then will back down the duty cycle to achieve equal shaft speeds. Three vehicle-speed sensors monitor the road speed of the vehicle and the rotating speed of the front and rear propshafts.
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