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 (circuit 1640) provides the power to the module and motor circuitry.

The transfer case encoder motor is a permanent magnet D.C. motor and gear reduction assembly. The encoder motor is controlled with a Pulse Width Modulated (PWM) circuit within the transfer case shift control module. It is located on the left hand side (drivers side) of the transfer case. When activated it turns the sector shaft of the transfer case to shift the transfer case. 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 Propshaft 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 Propshaft 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 indicator (AWD/4WD) lamp is part of the instrument cluster. Voltage is supplied to it by an 10 amp. fuse through circuit 39. The transfer case shift control module controls this lamp by providing a ground through circuit 1567. This lamp is used to inform the driver of the vehicle of malfunctions within the Automatic Transfer Case (ATC) system.