analog and resistor multiplexed inputs as well as
digital electronic inputs from other electronic mod-
ules in the vehicle electrical system through its
connection to the IPM and the Programmable Com-
munications 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 sys-
tems.
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
3.8.1 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 clus-
ter sends a Programmable Communications Inter-
face (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 mes-
sage) to the headlamps through four 9fuseless9
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 Run-
ning 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 instru-
ment 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 con-
tinuously 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.
3.8.2 RELAY CONTROLS
Adjustable Pedals Relay
If equipped, the adjustable pedals relay, when not
activated, supplies fused battery power to the ad-
justable 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 moni-
tored 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.
12
GENERAL INFORMATION
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