Dodge Ram 2004, Service Manual

Page: 27 / 642

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 moni-
tored for malfunctions.
Wiper High/Low Relay
The wiper switch is a direct input to the instru-
ment 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 con-
trolled and continuously monitored for malfunc-
tions.
Wiper On/Off Relay
The wiper switch is a direct input to the instru-
ment 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.
3.8.3 ELECTRICAL INPUTS
Module Battery Supply
12 Volt input for all FCM functions except head-
lamp 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 place-
ment 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 connec-
tion and that the Connector Positive Assurance
(CPA) is engaged. If the CPA is not properly en-
gaged, a voltage is sent to the FCM to be inter-
preted as an unseated connector which will set a
Diagnostic Trouble Code (DTC).
3.9 HEATING & A/C SYSTEM
3.9.1 SYSTEM AVAILABILITY
• Depending on the model, either a Single-Zone or
Dual-Zone HVAC system is available in these
vehicles.
3.9.2 SYSTEM CONTROLS
The Heater Control Module:
• is fully addressable with the DRBIII
t
.
•
communicates over the Programmable Commu-
nication Interface Multiplex System (PCI) Bus.
• controls blower motor operation, providing four
blower speeds (Low, M1, M2, & High).
• controls heated mirror and EBL operation (if
equipped).
•
controls electric door actuator operation.
The A/C-Heater Control Module:
• is fully addressable with the DRBIII
t
.
•
communicates over the Programmable Commu-
nication Interface Multiplex System (PCI) Bus.
• uses input from the evaporator temperature sen-
sor to prevent evaporator freeze up while main-
taining optimum cooling performance.
• provides an A/C request to the Powertrain Con-
trol Module (PCM) over the PCI Bus when com-
pressor operation is desired.
•
controls blower motor operation, providing four
blower speeds (Low, M1, M2, & High).
• controls heated mirror and EBL operation (if
equipped).
•
controls electric door actuator operation.
• A simplified control system for operation of the
mode, recirculation, and temperature control
actuators provides positive positioning with-
out the complexity of feedback from position
sensors. The A/C - Heater Control Module
knows the number of operating actuator revo-
lutions required for full door travel as well as
the number of actuator commutator pulses per
revolution. Using these parameters, the A/C -
Heater Control Module runs the actuator for
the number of commutator pulses that corre-
13
GENERAL INFORMATION