Front Control Module
FRONT CONTROL MODULEThe Front Control Module (FCM) is a microprocessor-based electrical control and interface center located in the engine compartment. When it is mated to the Power Distribution Center (PDC), it is referred to as the Integrated Power Module (IPM). The IPM, with its fuses and relays provides power and signal distribution throughout most of the vehicle. The FCM receives hard-wired analog and resistor multiplexed inputs as well as digital electronic inputs from other electronic modules in the vehicle electrical system through its connection to the IPM and the Programmable Communications Interface (PCI) data bus network. Based on these inputs and programming, the FCM uses high side drivers to provide direct power feeds and low side drivers to provide relay control for some of the vehicle's most critical electrical systems.
The FCM provides the following features:
Controlled Feeds
Headlamp power
Windshield washer pump motor
Relay Controls
Accessory relay
Adjustable pedals relay (when equipped)
Fog lamp relay (when equipped)
Horn relay
Park lamp relay
Wiper ON/OFF relay
Wiper high/low relay
Electrical Inputs
Headlamp battery supplies
Module battery supply
Power ground
Ignition switch RUN or START position status
Ignition switch START Only status
PCI bus
Brake lamp switch
Wiper park switch
Washer fluid level switch
Brake fluid level switch
Ambient Temperature sensor
Right park lamp outage
Left park lamp outage
Battery IOD
Battery (+) connection detection
Flash reprogramming voltage
Controlled Power Feeds
Headlamp Power
he headlamp switch is a direct input to the instrument cluster which is sometimes known as the Cab Control Node (CCN). The instrument cluster sends a Programmable Communications Interface (PCI) bus message to the FCM informing it of a headlamp switch status change. The FCM then turns power ON or OFF (depending on the bus message) to the headlamps through four "fuseless" circuits. These circuits are electronically controlled and continuously monitored for malfunctions. Power is supplied to each filament in a separate circuit. For vehicles equipped with Daytime Running Lamps (DRL), the FCM electronically steps down the headlamp voltage to provide the desired illumination levels.
Washer Pump Motor
The washer switch is a direct input to the instrument cluster. The instrument cluster sends a PCI bus message to the FCM informing it of a request to wash. The washer pump motor is then powered through low side control inside the FCM.
This circuit is electronically controlled and continuously monitored for malfunctions. In addition, the FCM electronically protects the washer pump motor from system voltages higher than 16 volts by automatically switching OFF the low side circuit. The low side circuit is connected to pin 45 in the FCM connector.
If the FCM receives a prolonged request to wash lasting 30 seconds or more, it will treat the request as a stuck switch condition and deactivate the washer pump motor. The FCM will not reactivate the washer pump motor until there is at least a two second break in the request to wash from the instrument cluster.
Relay Controls
Accessory Relay
The accessory relay works in conjunction with the FCM's power accessory delay features to control the operation of the radio, power windows, washer pump motors, wiper motor and power outlets. The accessory relay is turned ON by the FCM through the relay's low side control circuit. This circuit is electronically controlled and continuously monitored for malfunctions.
Depending on the ignition switch position, the accessory relay will remain ON or will time out and deactivate. The accessory relay remains ON in the RUN and ACCY ignition switch positions. In the UNLK and OFF positions, the relay will remain energized for 45 seconds and then deactivate. During this time-out period, if a driver or passenger door is opened, the relay will be deenergized immediately. While the ignition switch is in the START position, the relay will also drop out and then resume operation. Accessory relay operation is most noticeable by observing the operation of the radio.
Adjustable Pedals Relay
If equipped, the adjustable pedals relay, when not activated, supplies fused battery power to the adjustable pedals switch. If the FCM receives a bus message that the vehicle is in reverse or that the cruise control is engaged, it will apply a ground to the adjustable pedals relay control circuit. The ground will activate the relay which will open the power circuit to the adjustable pedals switch. The relay control circuit is continuously monitored for malfunctions which the FCM will report as DTC's.
Fog Lamp Relay
If equipped, the fog lamp switch is a direct input to the instrument cluster. The instrument cluster sends a PCI bus request to the FCM to turn ON the fog lamp relay. The fog lamp relay is then actuated by the FCM through low side control. This circuit is electronically controlled and continuously monitored for malfunctions. The FCM "learns" that the vehicle is equipped with fog lamps by reading the instrument cluster PCI bus message.
Horn Relay
The Horn Relay, which is internal to the IPM, is controlled by the FCM through PCI bus messages from the instrument cluster. These bus messages will be sent when either the horn switch is pressed which is hard wired to the instrument cluster, panic mode is requested from the RKE or for vehicle theft security reasons (if equipped). Under normal operating conditions, if the horn is activated for more than 30 seconds, the FCM will automatically deactivate the horn to prevent damage. The FCM will reactivate control of the relay after a 25-second cool-down period. The relay control circuit is continuously monitored for malfunctions that the FCM will report as DTC's.
Park Lamp Relay
The park lamp switch is a direct input to the instrument cluster. The instrument cluster sends a PCI bus request to the FCM to actuate the park lamp relay. The park lamp relay is then actuated through the low side control circuit. This circuit is electronically controlled and continuously monitored for malfunctions.
Wiper High/Low Relay
The wiper switch is a direct input to the instrument cluster. The instrument cluster sends a PCI bus request to the FCM to actuate the wiper high/low relay. The relay switches power between the low speed and high speed brush of the wiper motor. The wiper high/low relay is then actuated through the low side control circuit. This circuit is electronically controlled and continuously monitored for malfunctions.
Wiper ON/OFF Relay
The wiper switch is a direct input to the instrument cluster. The instrument cluster sends a PCI bus request to the FCM to actuate the wiper ON/OFF relay. The wiper ON/OFF relay is then actuated through the low side control circuit. This relay switches power to the wiper high/low relay. This circuit is electronically controlled and continuously monitored for malfunctions.
Electrical Inputs
Headlamp Battery Supplies
12 Volt input as battery supply voltage dedicated for headlamp switching circuits only.
Module Battery Supply
12 Volt input for all FCM functions except headlamp operation.
Power Ground
Ground source for all FCM functions
Ignition Switch RUN or START Position Status
12 Volt input to inform the FCM of the ignition switch status for related FCM functions.
Ignition Switch START Only Status
12 Volt input to allow the FCM to differentiate between the RUN/START and START only status for related FCM functions.
PCI Bus
Approximately 7.5 Volt input to allow the FCM to communicate with other modules on the PCI bus.
Brake Lamp Switch Status
12 Volt input from brake lamp switch for brake shift interlock functions.
Wiper Park Switch
Ground input used to determine the park placement of the wipers. The ground is also used as feedback to the FCM to determine wiper operating mode.
Washer Fluid Level Switch
Ground input from the washer fluid level switch which closes when washer fluid is low.
Right Park Lamp Outage
12 Volt input used to monitor the RH parking lamp circuit.
Left Park Lamp Outage
12 Volt input used to monitor the LH parking lamp circuit.
Battery IOD
A low current 12 Volt input to maintain microprocessor power when the FCM switches to low power consumption mode during ignition OFF.
Battery (+) Connection Detection
12 Volt supply used to monitor battery connection to the IPM. The battery connection to the IPM uses an internal switch to check integrity of the connection and that the Connector Positive Assurance (CPA) is engaged. If the CPA is not properly engaged, a voltage is sent to the FCM to be interpreted as an unseated connector which will set a Diagnostic Trouble Code (DTC).
Flash Programming Voltage
20 volt input. When the DRB III is connected and proper flash reprogramming sequence is selected, the 20 Volt signal will be applied to the FCM.