The transfer case shift control module uses the VIN information for calculations that are required for the different calibrations used based on axle ratio, transmission, tire size, and engine. The system does not know which calibration to use without this information.

The direct battery supply line (CKT 1640) provides the power to the module and motor circuitry.

The transfer case encoder motor is a permanent magnet DC motor and gear reduction assembly. The encoder motor is controlled with a pulse width modulated (PWM) circuit within the transfer case shift control module. This circuit consists of a power supply relay (Motor A) circuit that supplies voltage to the motor through CKT 1552. The Motor B circuit (CKT 1553) is a PWM driver that varies the duty cycle to control the amount of current through the motor to ground.

There are three vehicle speed sensors on the automatic transfer case (ATC), two on the rear output shaft and one on the front output shaft. Each vehicle speed sensor is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases as speed increases.

Vehicle Speed Sensor

One of the two on the rear output shaft is the vehicle speed sensor (VSS) input to the vehicle control module (VCM). The VCM sends this information to the transfer case shift control module via the Class 2 Serial Data bus.

Rear Transfer Case Vehicle Speed Sensor

The transfer case shift control module converts the pulsating AC voltage from the rear transfer case vehicle speed sensor to a Rear Propshaft Speed in RPM to be used for calculations. The Rear Propshaft Speed can be displayed with a scan tool.

Front Transfer Case Vehicle Speed Sensor

The transfer case shift control module converts the pulsating AC voltage from the front transfer case vehicle speed sensor to Front Propshaft Speed in RPM to be used for calculations, and to monitor the difference between the front and rear sensor speed. It is also used in the AUTO (Adapt) mode of operation to determine the amount of slip and the percent of torque to apply to the front axle. The Front Propshaft Speed can be displayed with a scan tool.

The SERVICE AWD/4WD lamp is an integral part of the cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle of malfunctions within the Automatic Transfer Case (ATC) system. The SERVICE AWD/4WD lamp is controlled by the transfer case shift control module via a Class 2 Serial Data message.