Initial Inspection and Diagnostic Overview
Four Wheel Drive (4WD) Systems Electronic Shift
Refer to Wiring Diagrams for Four Wheel Drive Systems for schematic and connector information.
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.
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 shift motor 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) sensor
- ignition switch
- gearmotor encoder assembly
Based on these inputs, the 4WD control module controls the shifis into 2WD, 4WD HIGH or 4WD LOW with the following outputs:
- gearmotor (clockwise)
- gearmotor (counterclockwise)
Neutral Tow
To transition the vehicle to neutral tow, the operator must:
- turn the ignition switch to the ON position
- place the mode select switch (MSS) in 2WD
- step on the brake
- place the transmission in NEUTRAL
- turn the ignition switch to the OFF position
- hold brake pedal down until neutral indicator illuminates (approximately four seconds).
- release the brake pedal.
When neutral tow is requested, the 4WD control module checks that the neutral tow feature is enabled, the baffery voltage is between 9 and 16 volts, the vehicle is in 2WD and the ignition switch is in the OFF position. Once these conditions are met, the 4WD control module checks for the presence of the neutral tow indicator lamp. If the indicator lamp is detected, the 4WD control module will request the transfer case shift motor position the transfer case into NEUTRAL. If any of the previous conditions are not met, the neutral tow feature will be suspended until the next neutral tow request.
Once all the doors are closed, the neutral tow indicator lamp will stay on until the battery saver relay enables the battery saver function. If any door is opened afier the battery saver function is enabled, the lamp will come back on until the transfer case is shified out of NEUTRAL or until the battery saver feature times out.
Inspection and Verification Electronic Shift
1. Verify the customer concern.
2. Visually inspect for obvious signs of mechanical or electrical damage.
3. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
4. If the cause is not usually evident, connect the diagnostic tool to the data link connector and select the vehicle to be tested from the diagnostic tool menu. If the diagnostic tool does not communicate with the vehicle:
- check that the program card is correctly installed.
- check the connections to the vehicle.
- check the ignition switch position.
5. If the diagnostic tool still does not communicate with the vehicle, refer to the diagnostic tool operating manual.
6. Carry out the DATA LTNK DIAGNOSTICS test. If the diagnostic tool responds with:
- SCP+ or SCP- circuit fault = ALL ECUS NO RESPINOT EQUIP, refer to module Communications network.
- NO RESPINOT EQUIP for 4WD control module, go to Pinpoint Test B.
- SYSTEM PASSED, retrieve and record the continuous diagnostic trouble codes (DTCs), erase the continuous DTCs and carry out the self-test diagnostics for the 4WD control module.
7. If the DTCs retrieved are related to the concern, go to the 4WD Control Module Diagnostic Trouble Code (DTC) Index.
8. If no DTCs related to the concern are retrieved, carry out the Electronic Shift Function Test. Refer to Functional Test Electronic Shift (Pinpoint Test A). Pinpoint Test A: ELECTRONIC SHIFT FUNCTIONAL TEST