Power In

Electronic Shift Transfer Case Schematic:

Power is supplied to the system at three points (P1, P2, and P3 in the schematic).
P1. This is a direct connection to the battery. This power drives the electric shift control motor and provides current to the instrument cluster lamps. This circuit goes to ground G1.
P2. The electronic shift control module is tied into the ignition circuit. This circuit provides power to the computer and goes to ground G2.
P3. Nighttime illumination is provided by a connection to the vehicle's nighttime illumination circuit, which goes to ground G3.

The Electronic Shift Control Module directs power depending on the position of the control switches. In the schematic, you will notice that INPUTS and OUTPUTS to and from the Shift Module are labeled A, B or C. A circuits are POWER CIRCUITS, B circuits are DATA CIRCUITS from SENSORS, and C circuits are ACTIVATING SWITCH and RELATED LAMP CIRCUITS.

The B circuits supply data from THREE sources: The Speed Sensor, the Motor Position Sensor, and either a Park/Neutral Position Switch (for automatic transmissions) or a Clutch Pedal Position switch (for manual transmissions).

The Speed Sensor is important because the vehicle must be stopped for a shift into or out of 4L. The shift module won't make the shift if the vehicle is moving. The shift module also won't make a shift to 4L or back unless the automatic transmission is in NEUTRAL, or the clutch is DEPRESSED on a manual transmission.

Shift Motor Rotation:

The Motor Position Sensor indicates the position of the Shift Motor Shaft. This shaft turns through approximately 270° and should STOP at THREE indexed points, 2H, 4H, and 4L. The Shift Control Module needs to know where the shaft is before making a new shift. When this sensor isn't functioning properly or the motor stops slightly off location, the Shift Control Module may become "confused."

The C circuits involve the switches on the vehicle's Control Panel. When everything is working properly, activating a switch will result in either a shift from 2H to 4H or back, or a shift from 4H to 4L or back. The default operating mode is 2H. This means that in the absence of other instructions, the Shift Control Module will assume that the vehicle should be in 2H. If there is a failure in the system during shifts or engine start up, it will default the vehicle to 2H and permit continued operation.