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Home >> Dodge or Ram Truck >> 2003 >> RAM 2500 Truck 2WD V8-5.7L VIN D >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Relays and Modules - Computers and Control Systems >> Body Control Module >> Description and Operation >> Functional Operation >> Front Control Module

Front Control Module

FRONT CONTROL MODULE
The 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:
- Brake lights
- Headlamp power
- Turn signals (front & rear)
- Windshield washer pump motor

Relay Controls
- Adjustable pedals relay (when equipped)
- Fog lamp relay (when equipped)
- Horn relay
- Park lamp relay
- Trailer tow relays
- Wiper on/off relay
- Wiper high/low relay

Electrical Inputs
- Module battery supply
- Power ground
- Ignition switch RUN or START position status
- PCI bus
- Wiper park switch
- Washer fluid level switch
- Ambient Temperature sensor
- Battery (+) connection detection

CONTROLLED POWER FEEDS

Headlamp Power
The 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.

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

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 DTCs.

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.

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). The relay control circuit is continuously monitored for malfunctions that the FCM will report as DTCs.

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 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

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.

PCI Bus
Approximately 7.5 volt input to allow the FCM to communicate with other modules on the PCI bus.

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.

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).
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