Electric 4WD Shifting

Transfer Case 4WD Selector Switch:

4WD Selector Switch Wiring Schematic:

OPERATION
On vehicles equipped with the Model 233 transfer case, there is no transfer case selector lever in the cab. The operator selects 4HI or 4LO by pushing a three-position (4HI, 4LO, 2HI) rocker-type selector switch mounted on the instrument panel. During normal driving the transfer case is in the 2HI mode. The switch is spring-loaded to the center position. When the transfer case is in 2HI both the 4HI and 4L0 switch circuits are open, and both lights are off. When shifting to 4HI or 4LO the rocker switch will still return to the center position and the 4HI or 4LO light will be on. The above image shows the wiring schematic of the transfer case selector switch.

Mode Shifts
Mode shifts are shifts from:

- 2HI to 4HI
- 4HI to 2HI

A mode shift can be accomplished in any gear position and at any vehicle speed. If the system is in 2HI, the operator can shift into 4HI merely by pressing and releasing the 4HI area of the selector rocker switch. The green 4HI status lamp flashes whenever a 2HI or 4HI shift is initiated and continues to flash until the TCCM completes the shift (or until 30 seconds elapses). After the shift into 4HI is accomplished, the 4HI status lamp remains lit to indicate that the system is in 4HI. The operator can shift from 4HI back to 2HI by again pressing 4HI on the selector switch. Again, the green 4HI status lamp flashes until the shift to 2HI is complete, and then extinguishes once the shift is complete. Both the 4HI and 4LO lamps remain oft when the vehicle is in 2HI.


Range Shifts
Range shifts are shifts between the HI and LO ranges, from:

- 2HI to 4LO
- 4HI to 4LO
- 4LO to 4HI

A range shift from 4L0 directly to 2HI cannot be made. The operator must first make range shift from 4LO to 4HI, then a mode shift from 4HI to 2HI.
A range shift can only be made with the automatic transmission in neutral or with the manual transmission clutch fully depressed. The vehicle speed must also be below three miles per hour before the shift can occur.
Whenever a shift into 4LO is initiated, the amber 4LO status lamp flashes and continues to flash until the TCCM completes the shift (or until 30 seconds elapses). The 4LO status lamp must glow steadily before the vehicle transmission is shifted into gear or before the clutch pedal is released. If a range shift is initiated when the transmission is engaged or when the vehicle speed is above 3 mph, the 4LO status lamp flashes for 30 seconds and no range shift actually occurs; the system returns to the position before the shift was initiated.