Electronic Shift Operation

NOTE: It is important to remember that the electronic shift transfer case does not have a selectable neutral position. Because of this, if vehicles equipped with electronic shift are to be towed for long distances, the rear driveshaft should be disconnected. If this is not done, the transfer case (which is protected by positive lubrication) will drive the transmission (which is not lubricated under these conditions), and may cause damage to the transmission.





This feature allows for the electronic shifting of the vehicle transfer case between 2WD, 4WD HIGH and 4WD LOW. The system mode is selected by the operator through a three-position rotary switch on the instrument panel.








The operator is informed which mode the system is in by two cluster indicator lamps, one for 4WD HIGH and one for 4WD LOW (in 4WD LOW, both lamps are on). The module accomplishes shifts between different system modes by interpreting inputs from 4x4 selector switch, the vehicle speed signal, and the transfer case contract plates. Based on these inputs, two relays (L2H and H2L directional control), the transfer case motor, and an output for the transfer case electric clutch, are used to shift into 2WD, 4WD HIGH, or 4WD LOW. The module will not allow shifts into 4WD LOW unless the brake is depressed, the vehicle is in NEUTRAL (with automatic transmission vehicles), the clutch is pressed (in manual transmission vehicles), and the speed is less than 3 mob.





The transfer case is equipped with a magnetic clutch, similar to an air conditioning compressor clutch, which is located inside the transfer case adjacent to the lockup sleeve. The clutch is used to spin up the front drive system from zero to vehicle speed in milliseconds. This spin-up allows the shift between 2H and 4H to be made at vehicle speeds listed in the vehicle owner's guide. The spin-up engages the front lock hubs. When the transfer case rear and front output shaft reach synchronous speed, the spring-loaded shift collar mechanically engages the mainshaft lockup hub to the chain-drive sprocket and the magnetic clutch is then deactivated. Shifts between 4H and 4L can only occur with the transmission safety switches closed. The vehicle's speed must also be within specified limits as determined by the Generic Electronic Module (GEM).

The electronic shift control system consists of a rotary switch control system, a GEM, a transfer case shift motor with an integral shift position sensor, a clutch pedal position switch or digital transmission range (DTR) sensor, and a brake signal input switch.

There is a control switch located on the instrument panel for fingertip shift control.

When the switch on the instrument panel is turned, there is a one second delay, then the electronic control module verifies the transfer case positions (2H, 4H or 4L). Next, the GEM looks at the shift position sensor and the digital transmission range (DTR) sensor or clutch pedal position switch (depending on transmission type) and brake pedal switch. If all conditions are correct to allow the desired shift, the electronic control module will tell the transfer case shift motor to execute the shift. After the shift has been made and the transfer case shift motor is off, the control module again looks at the shift position sensor to make sure the proper shift has been accomplished. Finally, the dash indicator light on the control panel will be illuminated by a signal from the GEM indicating the desired shift has been completed.