Grand Cherokee 2WD V6-3.7L (2008)
Control Unit: Description and Operation
Operation
OPERATION
POWER UP/DOWN
The Final Drive Control Module (FDCM) will power up with an OFF/ON transition of the hardwired ignition switch input, or with the presence of active
CAN C communications.
The FDCM will power down when the vehicle ignition switch transitions from ON to OFF, or there are no CAN C messages, or there are no system
requirements that dictate the controller to remain active
START-UP DIAGNOSTICS
When the FDCM is activated, the internal circuitry will undergo a diagnostic procedure. The controller will examine all inputs and outputs for short
circuits to ground, short circuits to battery and open circuits and will also verify proper CPU and memory operation. If a fault is detected, a message will
be sent out over the CAN C bus to the Cluster based Electronic Vehicle Information Center EVIC indicating that service is recommended.
After passing all diagnostic tests, the controller will receive and process inputs and produce the appropriate outputs. Proper monitoring of the controller
inputs and outputs performance will continue.
INPUTS/OUTPUTS
The following are inputs to the FDCM:
-
Lateral Accelerometer
-
Transfer Case Range Select Switch
-
Transfer Case Mode Sensor Signal
-
3 Direct Battery Feeds
-
Ignition RUN Sense
-
Sensor Grounds
-
Module Grounds
-
CAN C Bus
The following are outputs of the FDCM:
-
5V Sensor Supply
-
Transfer Case NEUTRAL Lamp
-
Front Electronic Limited Slip Differential Pressure Solenoid
-
Rear Electronic Limited Slip Differential Pressure Solenoid
-
Transfer Case Bi-directional Motor Control (A & B)
-
Switched B+ Solenoid Supply
-
Transfer Case Motor Brake Control
TRANSFER CASE RANGE SELECT SWITCH INPUT (NEUTRAL & 4HI/4LO SELECT SWITCH)
The FDCM will support circuitry which interfaces to the system's Transfer Case Range Select Switch, including a Transfer Case Range Select Switch
voltage supply and a Transfer Case Range Select Switch input. The purpose of this circuitry is to determine the mode currently being requested by the
operator via the resistance ladder network in the shifter assembly, where the Transfer Case Range Select Switch is packaged.
The NEUTRAL Select Switch Input will provide the operator with the ability to place the Transfer Case in Neutral. The 4HI/ 4LO Select Switch Input
will provide the operator with the ability to place the transfer case in 4HI or 4LO. The NEUTRAL Select Switch is a momentary contact switch and the
4HI/4LO Select Switch is a 2-position toggle or a momentary contact switch and both these switches are provided through a resistor network for
diagnostic purposes. The input will have an internal 1.0K +/- 1% pull-down resistor to ground.
As the selected position in the 4HI/4LO Switch varies and/or the NEUTRAL Switch is depressed or not, the resistance between the module's Transfer
Case Range Select Switches voltage supply and Transfer Case Range Select Switches input will vary. Hardware, software, and calibrations within the
FDCM will be provided that interpret the external resistance between the module's Transfer Case Range Select Switches voltage supply and Transfer
Case Range Select Switches inputs as given in the table below:
