Principles of Operation (How Does It Work?)

The Front Electronics Module (FEM) receives inputs and delivers outputs to a majority of the electronically controlled features which reside primarily in the front section of the vehicle. The Rear Electronics Module (REM) receives inputs and delivers outputs to a majority of the electronically controlled features which reside primarily in the rear section of the vehicle. The FEM and REM are configurable modules and must be correctly configured to the vehicle. The modules may also be configured to allow additional features or functions to be added to the vehicle. The FEM and REM do not have any optional window control configurations.

Driver Door Module (DDM)
The DDM receives inputs from the remote keyless entry transmitter and hardwired components such as the master window regulator control switch and delivers outputs in the form of Standard Corporate Protocal (SCP) network messages and hardwired component control. The DDM is a configurable module and must be correctly configured to the vehicle. The DDM may also be configured to allow additional features or functions to be added to the vehicle. The only DDM window feature that can be optionally configured is the window global open and close feature.

Module Inputs and Outputs
This system is unique in that many of the inputs that the FEM, REM and DDM receive are over the SCP communication network. These input messages come from other modules connected to the network. The FEM, REM and DDM will interpret the inputs, and in turn command the correct output that was requested. The modules also receive inputs which come directly from components which are hardwired to the modules such as the window regulator control switches.

One type of output the modules provide is over the SCP communication network in the form of messages. These types of outputs are usually generated from a module monitoring a hardwired input and sending a status message to another module. These outputs are commonly required by other modules to carry out their functions. The second type of output is the control of a component directly hardwired to the module.

Master Window Regulator Control Switch
The master window regulator control switch is hardwired to the DDM. Activating the master window regulator control switch sends a voltage signal to the DDM. The DDM will interpret the signal and control the power and ground to the driver front window regulator electric drive.

Activation of any of the passenger window switches on the master window regulator control switch sends a voltage signal to the DDM. The DDM interprets the signal and sends out the appropriate message over the SCP communication network. For the passenger front window, the FEM will interpret the DDM message and control the passenger front window regulator electric drive. For the rear passenger windows, the REM will interpret the DDM message and control the appropriate rear window regulator electric drive.

The driver one-touch down feature allows the driver front window to be lowered without holding the master window regulator control switch. Activation of the master window regulator control switch to the second down position sends a separate voltage signal to the DDM. The DDM will then control the power and ground to the driver front window regulator electric drive until a switch input is received or the motor reaches a stalled condition.

Passenger Window Power Supply
The REM controls the power supply to all three remote window regulator control switches. To protect the REM from a potential failure, the REM will remove power from the common passenger window power supply when a short to ground is sensed in any remote window regulator control switch, associated circuitry or the power output circuit of the REM. Power will be restored to the power output circuit upon a cycling of the ignition switch. If the REM output circuit is shorted to ground, the REM will immediately remove power from the common power supply circuit. If any remote window regulator control switch or its associated circuits are shorted to ground, the power will remain on the REM output circuit until the switch or circuit containing the short to ground is activated.

Passenger Window Lock-Out
The master window regulator control switch incorporates a passenger window lock-out switch. Activating the passenger window lock-out switch sends a separate voltage signal to the DDM. The DDM will then output a message to the REM. The REM will in turn remove power from the common passenger window power supply circuit. The rear window operation will be allowed from the master window regulator control switch only.

Passenger Front Power Window
The passenger front power window is controlled by the FEM. The passenger front window regulator control switch is hardwired directly to the FEM. Activating the passenger front window regulator control switch sends a voltage input to the FEM. The FEM then controls power and ground to the passenger front power window regulator electric drive, which is directly hardwired to the FEM. The voltage signal will only be received if the REM is supplying voltage to the remote window regulator control switch circuit.

The passenger front window can also be controlled by the master window regulator control switch. Activating the passenger front switch on the master window regulator control switch sends a voltage input to the DDM. The DDM will then send a message to the FEM over the network. The FEM then controls power and ground to the passenger front window regulator electric drive.

Left Rear (LR) and Right Rear (RR) Power Windows
The LR and RR power windows are controlled by the REM. Operating commands for the rear power windows are received in two forms, from the master window regulator control switch over the SCP communication network from the DDM, or directly from the LR or RR window regulator control switches, which are hardwired to the REM.

Activating the LR or RR switch on the master window regulator control switch causes the DDM to send a message to the REM over the SCP communication network. The REM will then control power and ground to the appropriate window regulator electric drive to raise or lower the window.

Activating either the LR or RR window regulator control switch sends a voltage signal to the REM. The REM will then control power and ground to the appropriate window regulator electric drive to raise or lower the window. A voltage signal will only be received if the window lock-out is OFF and the REM is supplying voltage to the remote window regulator control switch power circuit.

Rear Window Defrost
The rear window defrost feature is controlled by the REM, Powertrain Control Module (PCM), and the Dual Automatic Temperature Control (DATC) module. The rear window defrost switch is incorporated in the climate control head. When the switch is selected ON, the DATC module will send a message over the SCP communication network to the REM. The REM will then check its other messages for vehicle rpm from the PCM. If the rpm message is received, the REM will then ground the rear window defrost relay coil control circuit which is hardwired to the REM. The ground signal closes the rear window defrost relay which applies power to the rear window grid through the antenna isolator module. Fault management of the rear window defrost feature will prevent the rear window defrost from operating when a rpm or ignition switch invalid/missing data message is received.

Diagnosis
The FEM, REM and DDM constantly monitor systems under their control and report a concern in the form of a Diagnostic Trouble Code (DTC). DTCs can be retrieved with the New Generation STAR Tester or an equivalent tester through the SCP communication network.

This vehicle's design makes it unique in that electronic functions are divided into zones. The DDM controls features near the driver front door. The FEM controls features in the front portion of the vehicle and the REM controls the features in the rear portion. These systems rely heavily on the SCP communication network in order to transmit and receive messages. It is vital when diagnosing this vehicle's electronic systems, to understand:
^ where the input (command) originates.
^ all input information messages necessary in order for a feature to operate correctly.
^ which module(s) receive(s) the input (or command message).
^ if the module which received the input (message) controls the output of the feature, or does it output a message over the communication network to another module.
^ which module controls the output of the feature.

Delayed Accessory
Delayed accessory operation allows the power windows, radio and moon roof (if equipped) to operate for up to ten minutes after the ignition is turned to OFF. The delayed accessory function is controlled by the DDM. When the ignition switch is turned from RUN to OFF, the DDM will begin the timing sequence. If a door is opened or the ignition switch is activated to another position, the DDM will cancel the delayed accessory operation.

Heated Wiper Park
The heated wiper park grid (located within the lower painted area of the windshield) receives power from the heated wiper park relay located in the underhood auxiliary junction box. The heated wiper park relay coil is connected to a fused circuit from the underhood AJB. The heated wiper park relay is controlled by a switched ground from the DATC module controlled heated wiper park ON/OFF switch. The DATC module will disconnect current flow to the heated wiper park relay 10 minutes after activation or when manually switched OFF.