heater CHRYSLER VOYAGER 2001 User Guide
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Page 40 of 4284
3.5 COMMUNICATION
The Programmable Communication Interface or
PCI Bus is a single wire multiplexed network capa-
ble of supporting binary encoded messages shared
between multiple modules. The PCI bus circuit is
identified as D25 and is white with a violet tracer.
Additional tracer colors may be added to the violet
in order to distinguish between different module
connections. The modules are wired in parallel.
Connections are made in the harness using splices.
One splice called the Diagnostic Junction Port,
serves as the ªHubº of the bus. The Diagnostic
Junction Port provides an access point to isolate
most of the modules on the bus in order to assist in
diagnosing the circuit. The following modules are
used on the RG:
²Body Control Module
²Front Control Module
²Occupant Restraint Controller
²Left Side Impact Airbag Control Module
²Right Side Impact Airbag Control Module
²Controller Antilock Brake
²Powertrain Control Module
²Engine Control Module - Diesel Only
²Radio
²CD Changer
²Transmission Control Module
²Automatic Temperature Control Module
²A/C Heater Control Module (MTC)
²Sentry Key Immobilizer Module
²RKE/Thatcham Alarm Module
²Memory Seat/Mirror Module
²Overhead Console
²Mechanical Instrument Cluster
²Left Sliding Door Control Module
²Right Sliding Door Control Module
²Power Liftgate Module
Each module provides its own bias and termina-
tion in order to transmit and receive messages. The
bus voltage is at zero volts when no modules are
transmitting and is pulled up to about seven and a
half volts when modules are transmitting.
The bus messages are transmitted at a rate
averaging 10800 bits per second. Since there is only
voltage present when the modules transmit and the
message length is only about 500 milliseconds, it is
ineffective to try and measure the bus activity witha conventional voltmeter. The preferred method is
to use the DRBIIItlab scope. The 12v square wave
selection on the 20-volt scale provides a good view of
the bus activity. Voltage on the bus should pulse
between zero and about seven and a half volts.
Refer to the following figure for some typical dis-
plays.
The PCI Bus failure modes are broken down into
two categories. Complete PCI Bus Communication
Failure and individual module no response. Causes
of complete PCI Bus Communication Failure in-
clude a short to ground or battery on the PCI
circuit. Individual module no response can be
caused by an open circuit at either the Diagnostic
Junction Port or the module, or an open battery or
ground circuit to the affected module.
Symptoms of a complete PCI Bus Communication
Failure would include but are not limited to:
²All gauges on the MIC stay at zero
²All telltales on MIC illuminate
²MIC backlighting at full intensity
²Dashed lines in the overhead console ambient
temperature display
²No response received from any module on the PCI
bus (except the PCM)
²No start (if equipped with Sentry Key Immobi-
lizer)
Symptoms of Individual module failure could
include any one or more of the above. The difference
would be that at least one or more modules would
respond to the DRBIIIt.
Diagnosis starts with symptom identification. If a
complete PCI Bus Communication Failure is sus-
pected, begin by identifying which modules the
vehicle is equipped with and then attempt to get a
response from the modules with the DRBIIIt.Ifany
modules are responding, the failure is not related to
the total bus, but can be caused by one or more
modules PCI circuit or power supply and ground
circuits. The DRBIIItmay display ªBUS +/- SIG-
NAL OPENº or ªNO RESPONSEº to indicate a
communication problem. These same messages will
be displayed if the vehicle is not equipped with that
particular module. The CCD error message is a
default message used by the DRBIIItand in no way
indicates whether or not the PCI bus is operational.
The message is only an indication that a module is
either not responding or the vehicle is not equipped.
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GENERAL INFORMATION
Page 42 of 4284
3.7.6 EXTERIOR LIGHTING BATTERY
SAVER
The BCM monitors the status of, and controls, the
Park Lamps, Headlamps and Fog Lamp relays. If
any exterior lamps are left ON after the ignition is
turned OFF, the BCM will turn them OFF after 3
minutes.
3.7.7 AUTO HEADLAMPS
This feature is available on vehicles equipped
with both the Electrocromatic Mirror (ECM) and
the Compass/Mini-Trip Computer (CMTC). When
the BCM detects a day/night signal from the CMTC,
an ECM is present and Auto Headlamp mode is
selected.
3.8 FRONT CONTROL MODULE
The Front Control Module (FCM) is an electrical
control and interface center located in the engine
compartment. When it is mated to the Power Dis-
tribution Center (PDC), it is referred to as the
Intelligent Power Module (IPM). The IPM, with its
fuses and relays provides power and signal distri-
bution throughout most of the vehicle. The FCM
receives both hard wire and digital electronic inputs
from the vehicle electrical system through the PDC.
Based on these inputs and the ignition switch
position, it provides direct power feeds and relay
control to some of the vehicles' most critical electri-
cal systems.
The Front Control Module provides the following
features:
Controlled power feeds:
²Front airbag system
²Side airbag system
²Headlamp power
²EATX module power (4 speed only)
²Front washer motor
²Rear washer motor
²Brake shift interlock system
Relay controls:
²Fog lamp relay (when equipped)
²Park lamp relay
²Front wiper on relay
²Front wiper high/low relay
²Accessory relay
²Horn relay
²Front & rear blower relay
²Name brand speakers (NBS) relay
²Electronic back light (EBL) run only relay
²Cabin heater relayElectrical inputs:
²Headlamp battery supplies1&2
²Module battery supply
²Power ground
²Ignition switch RUN or START position status
²Ignition switch START only status
²PCI Bus
²Stop lamp switch
²Horn switch
²Back-up switch
²Wiper park switch
²Washer fluid level switch
²Brake fluid level switch
²Ambient temperature sensor
²Right park lamp outage
²Left park lamp outage
²Battery IOD
²Battery (+) connection detection
²Flash reprogramming voltage
3.8.1 CONTROLLED POWER FEEDS
Front airbag system
The FCM provides power to the Occupant Re-
straint Control (ORC) system through two ªfuse-
lessº circuits (ORC RUN/START, and ORC RUN
only). These circuits are electronically controlled
and continuously monitored for malfunctions.
Power is supplied while the ignition switch is in the
RUN and START positions on pin 48 of the FCM
connector, and in the RUN only position on pin 29.
Side airbag system
The FCM provides power to the Side Impact
Airbag Control Module (SIACM) system through
one ªfuselessº circuit. This circuit is electronically
controlled and continuously monitored for malfunc-
tions. Power is supplied in the ignition RUN and
START positions on pin 28 of the FCM connector.
Headlamp power
The headlamp switch is a direct input to the
BCM. The BCM sends a PCI Bus message to the
FCM informing it of a headlamp switch status
change. The FCM then turns on power to the
headlamps through four ªfuselessº circuits. These
circuits are electronically controlled and continu-
ously monitored for malfunctions. Power is supplied
to each filament in a separate circuit (RH low on pin
6, RH high on pin 4, LH low on pin 3 and LH high
on pin 5). For vehicles equipped with Daytime
Running Lamps (DRL), the FCM electronically
steps down the headlamp voltage to provide the
desired illumination.
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GENERAL INFORMATION
Page 44 of 4284
Front and rear blower relay
The blower control switch is part of the Automatic
Temperature Control (ATC) or A/C-Heater Control
Module, (Manual Temp). When the blower switch is
turned on, the ATC or A/C-Heater Control Module
sends a PCI Bus message to the FCM. The front and
rear blower relay is then powered through low side
control on pin 30 of the FCM. The relay provides the
high side to the blower motor, and the blower speed
is governed through low side control in the ATC or
A/C-Heater Control Module. This circuit is electron-
ically controlled and continuously monitored for
malfunctions.
Name Brand Speakers (NBS) relay
The NBS relay operates through the vehicle bus
interface between the radio and the FCM. When the
radio is turned on, the radio sends a PCI Bus
message to the FCM. The NBS relay is then pow-
ered on through low side control on pin 11 of the
FCM. The relay supplies power to the amplified
speaker, and ground is supplied through the radio.
This circuit is electronically controlled and contin-
uously monitored for malfunctions.
Electronic Back Light (EBL) relay
The rear defrost switch is part of the Automatic
Temperature Control or A/C-Heater Control Module
(Manual Temp). When the ignition switch is in the
RUN position and the rear defrost switch is turned
on, the ATC or A/C-Heater Control Module sends a
PCI Bus message to the FCM. The EBL run only
relay is then powered through low side control on
pin 31 of the FCM. The relay provides the high side
to the rear window defrost grid, and ground is
attached to the vehicle body. The FCM will only
allow the rear defrost to operate in the RUN posi-
tion. This circuit is electronically controlled and
continuously monitored for malfunctions.
Cabin Heater Relay
When the ignition is in Run, the FCM monitors
the PCI bus for the Cabin Heater Activation re-
quest. The A/C ± Heater Control Module initiates
this request only when all conditions for Cabin
Heater activation are favorable. The request carries
the status bit that the FCM requires to activate its
Cabin Heater Assist Control output. This output is
a low side driver (coming from FCM pin 15) which
supplies a ground signal to the Cabin Heater (pin
5). When the Cabin Heater receives this ground
signal input, it interprets this as an activation
signal. The FCM low side driver is also capable of
diagnostic sensing. The driver will sense an open
circuit when the driver is off, and will sense a short
to voltage when the driver is on. The FCM will set
DTCs for both of these types of faults. For addi-
tional information, refer to Cabin Heater under
General Information and Diagnostic Procedures in
the manual.3.8.3 ELECTRICAL INPUTS
Headlamp battery supplies1&2Ð12 volt
input on pins 1 and 2. Battery supply voltage for
switching headlamp circuits only.
Module battery supply Ð12 volt input on pin 9.
Battery supply voltage for all other FCM opera-
tions.
Power ground ÐGround source on pin 8 for all
FCM operations.
Ignition switch RUN or START position status
Ð12 volt input on pin 37. Allows the FCM to
determine the ignition switch status for related
FCM operations.
Ignition switch START only status Ð12 volt
input on pin 19. Allows the FCM to discriminate
between RUN/START input and START for related
FCM operations.
PCI Bus ÐApproximately 7.5 volt input on pin 22.
Allows the FCM to communicate with other mod-
ules on the vehicle bus.
Stop lamp Switch status Ð12 volt input on pin
44. Provides for brake shift interlock function.
Horn Switch ÐGround input on pin 17. Primary
means for engaging the horn.
Back-up switch ÐGround input on pin 39. Input
is converted to a PCI Bus status message for use by
other modules.
Wiper park switch ÐGround input on pin 16.
Used to determine park placement of wipers. Also
used as feedback to FCM to determine correct
operating mode of wipers.
Washer fluid level switch ÐGround input to
pull-up on pin 18. Ground is switched into the
circuit when washer bottle fluid level is low.
Brake fluid level switch ÐGround input to
pull-up on pin 36. Ground is switched into the
circuit when brake fluid level is low.
Ambient temperature sensor ÐResistive input
to pull-up on pin 25. Corresponding voltage level is
converted to a PCI Bus message for use by other
modules on the bus.
Right park lamp outage Ð12 volt input on pin
21. Used to determine if right park lamp circuit is
operating properly.
Left park lamp outage Ð12 volt input on pin 41.
Used to determine if left park lamp circuit is
operating properly.
Battery IOD Ð12 volt input on pin 20. The FCM
enters a low power consumption mode when the
ignition is turned OFF. This low current draw
battery supply keeps the microprocessor function-
ing in the low power mode.
Battery (+) connection detection Ð12 volt
input on pin 38. The battery connection on the PDC
incorporates the use of an internal switch to deter-
mine if the connector is properly mated and the
Connector Positive Assurance (CPA) is engaged. If
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GENERAL INFORMATION
Page 45 of 4284
the CPA is not properly engaged, a voltage on pin 38
will be interpreted as an unseated connector and a
fault will set.
Flash programming voltage Ð20 volt input on
pin 42. When a DRBIIItis connected and the
proper flash reprogramming sequence is selected,
the 20 volt signal will be applied through pin 42.
3.9 HEATING & A/C
3.9.1 AUTOMATIC TEMPERATURE
CONTROL (ATC)
3.9.1.1 CABIN HEATER
For vehicles equipped with a diesel engine, a
Cabin Heater is used in conjunction with the HVAC
system. The Cabin Heater is designed to supply the
vehicle's occupants with heat prior to the engine
reaching operating temperature. For additional in-
formation on this system, refer to Cabin Heater
under General Information and Diagnostic Proce-
dures in this manual.
3.9.1.2 SYSTEM OPERATION
The Automatic Temperature Control (ATC) sys-
tem provides fully adjustable three zone climate
control; Driver front zone, Passenger Front zone
and Rear zone. The following is a list of ATC
controls and features:
± a POWER button which allows the operator to
turn the system completely off.
± AUTO HIGH/LOW switch allows the operator
to select what rate (fan speed) the system will
provide the selected comfort level.
± DRIVER, REAR and PASSENGER rocker
switches to select desired temperature for each
zone.
± Recirculation button allows cooling air to be
recirculated which maximizes cooling ability.
± A/C select button allows the operator to turn
the A/C compressor off.
± Defroster button allows the operator to turn on
the defroster independently during automatic
control.
± Fan control rotary switch for selecting fan
speed.
± Mode rotary switch for selecting heating/
cooling direction.
± REAR SYSTEM rotary switch for activating
the Rear ATC Switch allowing intermediate
passenger control over rear climate control.
3.9.1.3 BLOWER MOTOR OPERATION
The Automatic Temperature Control (ATC) front
and rear blower control provides continuously vari-
able control of air flow rate to meet occupant
comfort requirements. Pulse width modulation of
the blower motor power allows the front and rear
blower to operate at any speed from off to full speed.
When front or rear blower operation is required, the
ATC sends a PCI Bus message to the Front Control
Module (FCM) requesting blower relay ON. The
FCM provides a ground for the front and rear
blower motor relay coils, activating both relays. The
front and rear blower relays provide 12 volts to
their respective blower motor power modules. Each
module provides a 12 volt blower motor control
signal to the ATC. The ATC provides a pulse width
modulated (duty-cycle) ground signal to this circuit
based on climate requirements. The higher voltage
on the signal circuit (less duty-cycle ground) the
lower the blower speed request. The lower voltage
on the signal circuit (more duty-cycle ground) the
higher the blower speed request.
3.9.1.4 INFRARED SENSORS
The ATC system uses infrared (I/R) sensors to
monitor and control oocupant comfort levels. This
sensing system replaces interior air temperature
and solar sensors which required complex control
programs to maintain occupant comfort levels. The
front I/R sensor is located in the instrument panel
center bezel outlet. The rear I/R sensor is located in
the rear overhead mounted ATC switch.
3.9.1.5 REAR ATC SWITCH
The rear ATC switch is mounted in the headliner.
The switch contains a rotary adjustment for fan
speed, a rotary adjustment for mode selection, a
push button switch for temperature selection and a
digital display of the selected temperature.
3.9.1.6 COOLDOWN TESTING
The ATC provides a feature referred to as a
Cooldown Test. This test is initiated using the
DRBIIItand is designed to check the performance
of the air conditioning system. The ATC will not
perform this test if the ambient air temperature is
below 12ÉC (53ÉF). During the test, the ATC com-
pares the ambient air temperature to the evapora-
tor temperature sensor. To pass the cooldown test,
the evap temperature sensor must drop -6ÉC (20ÉF)
below ambient temperature within 2 minutes of
start of test. At the completion of the cooldown test
the DRBIIItwill display one of the following mes-
sages indicating test outcome:
± Cooldown Test Passed
± Cooldown Test Failed
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GENERAL INFORMATION
Page 46 of 4284
± Evap Temp Sensor Shorted
± Evap Temp Sensor Open
± A/C Pressure Too Low
± A/C Pressure Too High
± Invalid Conditions for Cooldown Test, Evap
Temperature Too Low
If a message other than Cooldown Test Passed
occurs, refer to the appropriate symptom for diag-
nosis.
3.9.1.7 ACTIVE AND STORED TROUBLE
CODES
The Automatic Temperature Control (ATC) is
capable of storing Active and Stored trouble codes.
Active codes indicate a current fault in the system.
Stored codes indicate that a problem has occurred
in the system, however is not currently present.
Active codes cannot be erased until the problem
causing the code has been repaired. At this time the
Active code is converted to a Stored code, which can
be erased using the DRBIIIt.
3.9.2 MANUAL TEMPERATURE CONTROL
3.9.2.1 SYSTEM AVAILABILITY
Depending on the model, either a Single-Zone Air
Conditioning System or a Dual-Zone Air Condition-
ing System is currently available in these vehicles.
3.9.2.2 CABIN HEATER
For Vehicles equipped with a diesel engine, a
Cabin Heater is used in conjunction with the HVAC
system. The Cabin Heater is designed to supply the
vehicle's occupants with heat prior to the engine
reaching operating temperature. For additional in-
formation on this system, refer to Cabin Heater
under General Information and Diagnostic Proce-
dures in this manual.
3.9.2.3 ZONE CONTROL ± SINGLE-ZONE
The Single-Zone Air Conditioning System main-
tains incoming air temperature, airflow, fan speed,
and fresh air intake for the entire vehicle from the
instrument panel mounted A/C ± Heater Control
Module. The full range of temperature that the
system can produce in any mode for the entire
vehicle is available by positioning the blend control
to the desired range.
3.9.2.4 ZONE CONTROL ± DUAL-ZONE
The Dual-Zone Air Conditioning System main-
tains incoming air temperature, airflow, fan speed,
and fresh air intake for the entire vehicle from the
instrument panel mounted A/C ± Heater ControlModule. In addition, this system provides com-
pletely independent side-to-side control of incoming
air temperature. The full range of temperature that
the system can produce in any mode is available on
either side of the vehicle by positioning the inde-
pendent driver and passenger blend controls to the
desired range.
3.9.2.5 AIR DISTRIBUTION
The HVAC unit has five fully adjustable instru-
ment panel outlets. Side-window demister outlets
in the instrument panel eliminate door ducts and
door-to-instrument panel seals. A single, central
mounted outlet delivers air for defrosting the wind-
shield. Air exhausters allow air entering at the
front of the vehicle to flow out the back to the rear
occupants. Mid-cabin comfort control directs only
cooling air flow to the intermediate seat occupants
through outlets at the rear of each front door trim
panel. Air is supplied to these outlets from the
instrument panel through ducts in the doors that
use molded seals at the instrument panel to prevent
air leakage. Wide outlets under the front seats with
directional dividers distribute heated air across the
floor to the intermediate seat occupants. Ducts in
the center of the vehicle under the carpet deliver air
from the HVAC unit to these outlets. Models
equipped with Dual-Zone A/C systems also include
a dust and odor air filter installed in the HAVC
housing.
3.9.2.6 DOOR ACTUATORS
The electric door actuators are a two-wire design.
Each door actuator uses a similar connector wired
directly to the A/C ± Heater Control Module. Single-
Zone systems have one blend door actuator, one
mode door actuator, and one recirculation door
actuator. Dual-Zone systems have two blend door
actuators, one mode door actuator, and one recircu-
lation door actuator. All of the door actuators are
accessible from the vehicle's interior.
3.9.2.7 DOOR ACTUATOR CONTROL
The A/C ± Heater Control Module knows the
number of operating actuator revolutions required
for full door travel as well as the number of actuator
commutator pulses per revolution. Using these pa-
rameters, the A/C ± Heater Control Module runs
the actuator for the number of commutator pulses
that correspond to the desired door position. To
maintain accuracy, the system recalibrates itself
periodically at known zero and full travel condi-
tions.
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GENERAL INFORMATION
Page 47 of 4284
3.9.2.8 HVAC SYSTEM RELAYS
The Integrated Power Module (IPM) houses and
provides power to the A/C Clutch Relay and Front
Blower Motor Relay.
3.9.2.9 EVAPORATOR TEMPERATURE
SENSOR
An evaporator temperature sensor, located on the
A/C expansion valve under the hood, replaces the
previously used fin sensor.
3.9.2.10 A/C ± HEATER CONTROL
MODULE, SWITCH OPERATION
Power Switch
The Power Switch is a momentary contact switch.
The switch LED illuminates when the switch is on.
The Power Switch setting is remembered during
power down.
Rear Window Defogger Switch
The Rear Window Defogger Switch is a momen-
tary contact switch. Toggling the switch results in
the A/C ± Heater Control Module sending a change
of state message to the FCM to provide rear window
defogger activation or deactivation respectively.
The switch LED illuminates when the switch is on.
Recirculation Switch
The Recirculation Switch is a momentary contact
switch. Toggling the switch on results in the A/C ±
Heater Control Module signaling the actuator to
close the fresh-air door. Toggling the switch off
results in the A/C ± Heater Control Module signal-
ing the actuator to open the fresh-air door. The
switch LED illuminates when the switch is on.
When the Power Switch is off, the A/C ± Heater
Control Module closes the fresh-air door to prevent
outside air from entering the passenger compart-
ment. The recirculation mode will cancel whenever
defrost is requested. Pressing the Recirculation
Switch while in defrost mode will illuminate the
Recirculation Switch LED, but only while the but-
ton is pressed. Under this circumstance, the recir-
culation request will be denied and the fresh-air
door will remain in the fresh position. All door
positions are determined relative to the number of
commutator pulses required to provide full travel of
the door. On command, the A/C ± Heater Control
Module runs the actuator for the number of pulses
corresponding to the desired door position.
A/C Switch
The A/C Switch is a momentary contact switch.
Toggling the switch results in the A/C ± Heater
Control Module sending a change of state message
to the Powertrain Control Module (PCM ± gasoline)or Engine Control Module (ECM ± diesel) to provide
A/C compressor clutch activation or deactivation
respectively. The A/C ± Heater Control Module will
only provide this request if EVAP function is found
acceptable. The Power Switch must be on to make
the A/C switch active. The switch LED illuminates
when the switch is on. The A/C Switch setting is
remembered during power down.
Blower Switch
The rotary Blower Switch has five positions, Low,
M1, M2, M3, and High. The Power Switch must be
on to make the Blower Switch active. Toggling the
Power Switch results in the A/C ± Heater Control
Module sending a request to the FCM to provide
blower motor activation or deactivation respec-
tively.
Blend Switch ± Single Zone
The single rotary Blend Switch has multiple
detents to control the full range of temperature that
the system can produce in any mode. Rotating the
switch results in the A/C ± Heater Control Module
signaling the actuator to move the blend door. All
door positions are determined relative to the num-
ber of commutator pulses required to provide full
travel of the door. On command, the A/C ± Heater
Control Module runs the actuator for the number of
pulses corresponding to the desired door position.
Blend Switch ± Dual Zone
The dual sliding Blend Switches have multiple
detents to control the full range of temperature that
the system can produce an any mode. The upper
slide pot controls the driver-side blend door, while
the lower slide pot controls the passenger-side
blend door. Sliding the switch results in the A/C ±
Heater Control Module signaling the actuator to
move the blend door. All door positions are deter-
mined relative to the number of commutator pulses
required to provide full travel of the door. On
command, the A/C ± Heater Control Module runs
the actuator for the number of pulses corresponding
to the desired door position.
Mode Switch
The single rotary Mode Switch has 13 detents to
either direct airflow to the panel outlets, a mix of
floor and panel outlets, floor outlets, a mix of floor
and defrost outlets, or defrost outlets. Rotating the
switch results in the A/C ± Heater Control Module
signaling the actuator to move the mode door. All
door positions are determined relative to the num-
ber of commutator pulses required to provide full
travel of the door. On command, the A/C ± Heater
Control Module runs the actuator for the number of
pulses corresponding to the desired door position.
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GENERAL INFORMATION
Page 48 of 4284
3.9.2.11 HVAC DIAGNOSTICS
The A/C ± Heater Control Module is fully addres-
sable with the DRBIIIt. Two of the Control Mod-
ule's diagnostic capabilities that the DRBIIItwill
actuate include the A/C Cooldown Test to test A/C
system performance and the HVAC Door Recalibra-
tion Test to determine actuator travel span. After
performing either test, the Control Module will
display one or more messages on the DRBIIIt
screen. The message will indicate either that the
HVAC system passed the test or that there is a fault
currently active in the HVAC system. The DRBIIIt
can also extract active and stored Diagnostic Trou-
ble Codes (DTCs) from the control module. Active
DTCs are faults that currently exit in the HVAC
system. Active DTCs cannot be erased until the
condition causing the code is repaired. Stored DTCs
are faults that occurred in the HVAC system since
the control module received the last ªclear diagnos-
tic infoº message.
3.10 CABIN HEATER
NOTE: The Cabin Heater, also known as the
Diesel Cabin Heater Assist (DCHA), will be
referred to as the DCHA throughout most of
the General Information and the Diagnostic
Procedures in this manual.
3.10.1 GENERAL SAFETY INFORMATION
WARNING: DO NOT OPERATE THE DCHA IN
AN ENCLOSED AREA SUCH AS A GARAGE
THAT DOES NOT HAVE EXHAUST
VENTILATION FACILITIES. ALWAYS VENT
THE DCHA's EXHAUST WHEN OPERATING
THE DCHA. FAILURE TO FOLLOW THESE
INSTRUCTIONS MAY RESULT IN PERSONAL
INJURY OR DEATH.
WARNING: ALLOW THE DCHA ASSEMBLY
TO COOL BEFORE PERFORMING A COM-
PONENT INSPECTION/REPAIR/REPLACE-
MENT. FAILURE TO FOLLOW THESE
INSTRUCTIONS MAY RESULT IN PERSONAL
INJURY.
WARNING: ALWAYS DISCONNECT THE
VEHICLE'S BATTERY PRIOR TO PER-
FORMING ANY TYPE OF WORK ON THE
DCHA. FAILURE TO FOLLOW THESE
INSTRUCTIONS MAY RESULT IN PERSONAL
INJURY OR DEATH.WARNING: NEVER ATTEMPT TO REPAIR THE
DCHA HEATER MODULE OR ANY OF ITS
INTERNAL COMPONENTS. ALWAYS PER-
FORM DCHA COMPONENT REPLACEMENT
IN ACCORDANCE WITH THE SERVICE
INFORMATION. FAILURE TO FOLLOW
THESE INSTRUCTIONS MAY RESULT IN
PERSONAL INJURY OR DEATH.
CAUTION: Do not actuate the DCHA Field
Mode Test with the engine off. Failure to
follow these instructions may result in
internal damage to the DCHA Heater Module.
CAUTION: Always Perform The Cabin Heater
Pre-Test Prior To Performing Any Other Cabin
Heater Test For The Test Result To Be Valid.
NOTE: Do not disconnect the vehicle's
battery or the DCHA's main power-supply
while the DCHA is in operation or in
run-down mode. Failure to follow these
instructions may result in excess emissions
from the DCHA Heater Module.
NOTE: Failure to prime the Dosing Pump
after draining the DCHA fuel line will prevent
DCHA heater activation during the first
attempt to start the heater. This will also set a
Diagnostic Trouble Code (DTC) in the DCHA
Control's memory. Do not perform the Dosing
Pump Priming Procedure if an attempt was
made to start the DCHA without priming the
Dosing Pump first. This will put excess fuel
in the DCHA Heater Module and cause smoke
to emit from the DCHA exhaust pipe when
heater activation occurs.
NOTE: Waxed fuel can obstruct the fuel line
and reduce flow. Check for the appropriate
winter grade fuel and replace as necessary.
3.10.2 COMPONENT DESCRIPTION AND
OPERATION
3.10.2.1 DCHA ASSEMBLY
The DCHA is a supplemental heater designed to
pre-heat the engine's coolant in order to supply the
vehicle's occupants with heat prior to the engine
reaching operating temperature. The DCHA assem-
bly mounts underneath the vehicle on the left side
floor pan near the front door opening. The DCHA
assembly connects to the vehicle's heater hoses and
has a fuel supply line that connects to the vehicle's
fuel tank.
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Page 49 of 4284
The DCHA assembly consists of a:
²combustion air fan assembly
²burner housing
²burner insert
²control unit/heat exchanger
²combustion chamber
²dosing pump
3.10.2.2 COMBUSTION AIR FAN
The combustion air fan assembly includes the:
²combustion air fan
²combustion air fan inlet
²fuel supply inlet
The combustion air fan delivers the air required
for combustion from the combustion air inlet to the
burner insert.
3.10.2.3 BURNER HOUSING
The burner housing includes the:
²coolant inlet
²coolant outlet
²exhaust outlet
The burner housing accommodates the burner
insert and is combined with the control unit/heat
exchanger as an assembly.
3.10.2.4 BURNER INSERT
The burner insert includes the:
²combustion pipe fuel cross section
²glow plug/flame sensor
Inside the burner insert fuel is distributed across
the combustion pipe fuel cross section. Combustion
of the fuel/air mixture takes place within the com-
bustion pipe to heat the exchanger. The glow plug/
flame sensor located in the burner insert ignites the
fuel/air mixture during heater start up. After heater
start up, the glow plug/flame sensor operates in the
flame sensor function. The glow plug/flame sensor
designed as an electrical resistor is located in the
burner insert opposite the flame side.
3.10.2.5 CONTROL UNIT/HEAT
EXCHANGER
The control unit/heat exchanger includes the:
²control unit
²temperature sensor
²overheat protection
²heat exchanger
²connector terminal
The control unit controls and monitors combus-
tion operation. The control unit is ventilated bymeans of a ventilation hose routed from the com-
bustion air collector compartment of the burner.
The heat exchanger transfers the heat generated by
combustion to the coolant circuit. The control unit/
heat exchanger and the burner housing are an
assembly and must not be disassembled.
The temperature sensor senses the coolant tem-
perature in the heat exchanger as an electrical
resistance. This signal is sent to the control unit for
processing.
The overheat protection, controlled by the tem-
perature resistor, protects the heater against undue
operating temperatures. The overheat protection
will switch the heater off if the water temperature
exceeds 105ÉC (221ÉF).
3.10.2.6 DOSING PUMP
The dosing pump is a combined delivery, dosing,
and shut-off system for the fuel supply of the heater.
The dosing pump receives its supply of fuel from the
vehicle's fuel tank.
3.10.3 OPERATION
3.10.3.1 ACTIVATION
When the ignition is in Run, the FCM monitors
the PCI bus for the Cabin Heater Activation re-
quest. The A/C ± Heater Control Module initiates
this request only when all conditions for Cabin
Heater activation are favorable (see below). The
request carries the status bit that the FCM requires
to activate its Cabin Heater Assist Control Output.
This output is a low side driver (coming from FCM
pin 15) which supplies a ground signal to the Cabin
Heater (pin 5). When the Cabin Heater receives this
ground signal input, it interprets this as an activa-
tion signal. The FCM low side driver is also capable
of diagnostic sensing. The driver will sense an open
circuit when the driver is off, and will sense a short
to voltage when the driver is on. The FCM will set
DTCs for both of these types of faults.
The DCHA will activate only when the:
²engine is running.
²coolant temperature is below 66ÉC (151ÉF).
²fuel tank has greater than 1/8 of a tank of fuel.
²Power switch on the A/C ± Heater Control Module
is on.
²Blend Control on the A/C ± Heater Control Mod-
ule is set above 95% reheat.
²Front Control Module (FCM) sees the Cabin
Heater Activation request that is bussed from the
A/C ± Heater Control Module.
When the DCHA starting sequence begins, the
glow plug and the combustion air fan are activated.
After 30 seconds, the fuel dosing pump begins oper-
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GENERAL INFORMATION
Page 50 of 4284
ating and the combustion air fan operation is sus-
pended for 3 seconds. Subsequently, the combustion
air fan speed is increased in two ramps within 56
seconds to nearly full load operation. After a stabi-
lization phase of 15 seconds, the combustion air fan
speed is again increased in a ramp within 50
seconds to nearly full load. After reaching full load
fuel delivery, the glow plug is deactivated and the
combustion air fan operation is increased to full
load. During the subsequent 45 seconds, as well as
in normal operation, the glow plug functions as a
flame sensor to monitor the flame condition. After
all these events, the automatically controlled heat-
ing operation starts.
In case of a no flame or a flame out condition, a
restart is automatically initiated. If the no flame
condition persists, fuel delivery is stopped and the
heater enters an error lockout mode with a run-
down of the combustion air fan. This will set one or
more DTCs in the DCHA Control's memory. If six
continuous attempts to start the heater fail due to
one or more faults in the DCHA system, the heater
enters a heater lockout mode. This will set DTC
B1813 along with any other fault(s) that the DCHA
Control identified.
3.10.3.2 HEATING
During the automatically controlled heating op-
eration, when the coolant temperature reaches
72ÉC (162ÉF), the heater will switch to a part load
operation. When the coolant temperature reaches
75ÉC (167ÉF) or if the heater runs for longer than 76
minutes the heater will switch to a control idle
period. If the coolant temperature drops to 71ÉC
(160ÉF) during a control idle period, the heater will
perform a regular starting sequence into full load
operation. A drop in coolant temperature to 65ÉC
(149ÉF) during part load operation will cause the
heater to switch to a full load operation.
3.10.3.3 DEACTIVATION
The DCHA will deactivate if the:
²engine is turned off.
²coolant temperature reaches 75ÉC (167ÉF).
²heater runs longer than 76 minutes.
²fuel tank has less than 1/8 of a tank of fuel.
²Power switch on the A/C ± Heater Control Module
is off.
²Blend Control on the A/C ± Heater Control Mod-
ule is set below 75% reheat.
When the heater is deactivated, the combustion
stops and a run-down sequence begins. During the
run-down sequence, the combustion air fan contin-
ues operation to cool down the heater. The fan is
automatically switched off after the run-down se-
quence is complete. The run-down time and thecombustion air fan speed depend on the heater
operating condition at the time of deactivation.
Run-down time is approximately 175 seconds when
deactivated in full load operation and approxi-
mately 100 seconds when deactivated in part load
operation.
3.10.4 DIAGNOSTICS
The DCHA is fully addressable with the DRBIIIt.
System tests include a Field Mode Test to activate
the DCHA for diagnostic testing purposes. The
DCHA Control will store up to three DTCs in its
memory. If the Controller detects a new fault in the
DCHA system, one that is not already stored in its
memory, it will clear the oldest of the three stored
DTCs, and it will store the new fault's DTC. If the
Controller detects a reoccurrence of a stored fault, it
will overwrite that fault's DTC with the most recent
occurrence.
3.11 INSTRUMENT CLUSTER
The Instrument Cluster receives and sends mes-
sages to other modules via the PCI bus circuit. The
indicator lamps will illuminate briefly for a bulb
check when the ignition is turned from off to run.
All of the gauges receive their information via the
PCI bus from the powertrain control module and
body control module.
The gauges and the LEDs are not individually
replaceable thereby requiring complete replace-
ment of the Instrument Cluster if a repair is neces-
sary. In the event that the Instrument Cluster loses
communication with other modules on the PCI bus,
the cluster will display ªno busº in the VF display.
The Trip/Reset button is used to switch the dis-
play from trip to total mileage. Holding the button
when the display is in the trip mode will reset the
trip mileage. This button is also used to put the
cluster in self-diagnostic mode. The odometer dis-
play uses blue-green vacuum fluorescent digital
characters.
On base vehicles, the Instrument Cluster has
three gauges: Speedometer, Fuel and Engine Cool-
ant Temperature. A red dot moves transversely
through openings in the Instrument Cluster face
(P-R-N-D-2-1) to indicate the gear selected.
With all other models, the Instrument Cluster
also includes a Tachometer and uses a vacuum-
fluorescent shift indicator.
The odometer display and door/liftgate ajar indi-
cators turn on when a door is opened to assist both
the customer and service technician to view the
odometer without turning the ignition on.
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GENERAL INFORMATION
Page 59 of 4284
WARNING: BEFORE ROAD TESTING A
VEHICLE, BE SURE THAT ALL
COMPONENTS ARE REASSEMBLED.
DURING THE TEST DRIVE, DO NOT TRY TO
READ THE DRBIIITSCREEN WHILE IN
MOTION. DO NOT HANG THE DRBIIITFROM
THE REAR VIEW MIRROR OR OPERATE IT
YOURSELF. HAVE AN ASSISTANT
AVAILABLE TO OPERATE THE DRBIIIT.
5.0 REQUIRED TOOLS AND
EQUIPMENT
DRBIIIt(diagnostic read-out box)
Jumper wires
Ohmmeter
Voltmeter
Sentry Key Tester
Test Light
8310 Airbag System Load Tool
8443 SRS Airbag System Load Tool
Diagnostic Junction Port Tester 8339
6.0 GLOSSARY OF TERMS
ABSantilock brake system
ACMairbag control module
AECMairbag electronic control module
(ACM)
ASDMairbag system diagnostic module
(ACM)
AT Cautomatic temperature control
BCMbody control module
CABcontroller antilock brake
CMTCcompass/mini-trip computer
CPAconnector positive assurance
DABdriver airbag
DCHAdiesel cabin heater assist
(cabin heater)
DLCdata link connector
DTCdiagnostic trouble code
DRdriver
EBLelectric back lite (rear window de-
fogger)ECMEngine control module
EVICelectronic vehicle information center
FCMfront control module
GCCGulf Coast Countries
HVACheater ventilation, air conditioning
IPMintelligent power module
LDUlower drive unit
LHDLeft Hand Drive
MICmechanical instrument cluster
MTCmanual temperature control
MSMMmemory seat/mirror module
OBDon board diagnostics
ODOodometer
ORCoccupant restraint controller
PA Bpassenger airbag
PASSpassenger
PCIProgrammable Communication In-
terface (vehicle communication bus)
PCMpowertrain control module
PDCpower distribution center
PLGpower liftgate
PLGMpower liftgate module
PSDpower sliding door
PSDMpower sliding door module
PWMpulse width modulated
RHDRight Hand Drive
RKEremote keyless entry
SABseat airbag
SBTseat belt tensioner
SIACMside impact airbag control module
SKIMsentry key immobilizer module
SKISsentry key immobilizer system
SQUIBalso called initiator (located inside
airbag)
SRSsupplemental restraint system
TCMtransmission control module
VFDvacuum fluorescent display
VTSSvehicle theft security system
30
GENERAL INFORMATION