Principles of Operation

Four-Wheel Drive Systems-Electronic Shift





Special Tool(s)

Principles of Operation
Transfer Case-Electronic Shift
The four-wheel drive electronic shift-on-the-fly feature electrically shifts the vehicle transfer case between 2WD, 4WD HIGH, and 4WD LOW. The system mode is selected by the operator through the mode select switch (MSS) on the instrument panel. The operator is informed which mode the system is in by two instrument cluster indicators: one for 4WD HIGH which appears as 4WD HIGH, and one for 4WD LOW, which appears as 4WD LOW. Shifts into 4WD HIGH can be made at any speed. When shifting into 4WD HIGH with the vehicle stationary, tooth blockage may occur preventing shift completion. When the vehicle is driven above 8 km/h (5 mph) the shift will complete. When shifting in or out of 4WD LOW, the four-wheel drive (4WD) control module requires that the vehicle speed be less than 5 km/h (3 mph), the brake pedal be applied, and the transmission be in NEUTRAL (automatic transmission) or the clutch pedal be depressed (manual transmission).

The gearmotor encoder assembly is mounted externally on the transfer case. It drives a rotary cam, which moves the mode fork and range fork within the transfer case between the 4WD HIGH, 4WD LOW, and 2WD range positions.

The four-wheel drive (4WD) control module controls the gearmotor encoder assembly that shifts between 4WD HIGH, 4WD LOW, and 2WD modes.
The 4WD control module accomplishes shifts by interpreting inputs from the following:
^ mode select switch (MSS)
^ vehicle speed signal
^ encoder plate position
^ brake pedal switch
^ digital transmission range (TR)
^ ignition switch
^ gearmotor encoder assembly

Based on these inputs, the 4WD control module controls the shifts into 2WD, 4WD HIGH or 4WD LOW with the following outputs:
^ gearmotor (clockwise)
^ gearmotor(counterclockwise)