Transfer Case: Description and Operation

Cross-sectional View





Control System





ALL-MODE 4WD TRANSFER BASIC CONTROL





HYDRAULIC CONTROL CIRCUITS

OUTLINE
All-mode 4WD transfer is controlled by the transfer control unit and sensors.
If a malfunction occurs in the all-mode 4WD system, the 4WD warning lamp lights up to indicate the system malfunction. There are two ways to identify the cause of the malfunction.
1. Performing the self-diagnosis. (The 4WD warning lamp will indicate what kind of malfunction has occurred by flickering.)
2. Performing diagnosis using CONSULT-II.





CONTROL SYSTEM DIAGRAM





INDICATIONS OF 4WD WARNING LAMP





Location of Electrical Parts

Description of Electrical Parts
TRANSFER MOTOR
1. The transfer motor drives the sub-oil pump to provide proper lubrication and oil pressure control when the vehicle is at standstill, during low-speed operations or is being driven in reverse.
2. The main oil pump is operated by the driving force of the mainshaft. In other words, sufficient oil pressure buildup does not occur when the vehicle is at standstill or during low-speed operations. While the vehicle is being driven in reverse, the main oil pump rotates in the reverse direction. Therefore the main oil pump does not discharge oil pressure. During any of the above vehicle operations, the transfer motor drives the sub-oil pump to compensate for insufficient oil pressure.
3. The transfer motor operates as follows:
1. The motor relay turns OFF in the 2WD mode.
2. The motor relay operates as described in the table below in modes other than the 2WD mode.





Table 1





Table 2

NOTE: OFF (after 2.5 seconds have elapsed.)

4. 4WD shift switch, PNP switch, Neutral-4LO switch, vehicle speed sensor and throttle position sensor are used in conjunction with the transfer motor.

WAIT DETECTION SWITCH
1. The wait detection switch releases the "booming" torque produced in the propeller shaft. After the release of the "booming" torque, the wait detection switch helps provide the 4WD lock gear (clutch drum) shifts. A difference may occur between the operation ("4LO" to "4H" shift only) of the 4WD shift switch and actual drive mode. At this point, the wait detection switch senses an actual drive mode.
2. The wait detection switch operates as follows:
4WD lock gear (clutch drum) locked: ON
4WD lock gear (clutch drum) released: OFF
3. The wait detection switch senses an actual drive mode and the 4WD shift indicator lamp indicates the vehicle drive mode.

2-4WD SHIFT SOLENOID VALVE
The 2-4WD shift solenoid valve operates to apply oil pressure to the wet, multiplate clutch, depending on the drive mode. The driving force is transmitted to the front wheels through the clutch so the vehicle is set in the 4WD mode. Setting the vehicle in the 2WD mode requires no pressure buildup. In other words, pressure force applied to the wet, multiplate clutch becomes zero.

LINE PRESSURE SWITCH
1. With the transfer system design, control of the oil pressure provides the transmission of drive torque to the front wheels. The main pressure to control the oil pressure is referred to as the line pressure.
The line pressure switch determines whether or not adequate line pressure has built up under different operating conditions.
2. The line pressure switch turns ON when line pressure is produced.
3. The line pressure switch senses line pressure abnormalities and turns the 4WD warning lamp ON.