1998 DODGE RAM 1500 Iod fuse

²87A (Normally Closed)- This terminal is con-
nected to the normally closed fixed contact point of
the relay.
The rear window defogger relay cannot be adjusted
or repaired. If the relay is damaged or faulty, it must
be replaced.
OPERATION
The rear window defogger relay is an electrome-
chanical switch that uses a low current input from
the integrated power module (IPM) to control the
high current output to the rear window defogger
grid. The movable common feed contact point is held
against the fixed normally closed contact point by
spring pressure. When the relay coil is energized, an
electromagnetic field is produced by the coil wind-
ings. This electromagnetic field draws the movable
relay contact point away from the fixed normally
closed contact point, and holds it against the fixed
normally open contact point. When the relay coil is
de-energized, spring pressure returns the movable
contact point back against the fixed normally closed
contact point. The resistor or diode is connected in
parallel with the relay coil in the relay, and helps to
dissipate voltage spikes and electromagnetic interfer-
ence that can be generated as the electromagnetic
field of the relay coil collapses.
The rear window defogger relay terminals are con-
nected to the vehicle electrical system through a
receptacle in the IPM. The inputs and outputs of the
rear window defogger relay include:
²The common feed terminal (30) receives a bat-
tery current input from fuse 27 (15 amp) in the IPM
through a fused B(+) circuit at all times.²The coil ground terminal (87) receives a ground
input from the A/C-heater control when the A/C-
heater control electronically pulls the control circuit
to ground.
²The coil battery terminal (85) receives a battery
current input from fuse 36 (10 amp) in the IPM
through a fused B(+) circuit only when the ignition
switch is in the Run position.
²The normally open terminal (86) provides a bat-
tery current output to the rear window defogger and
heated power mirrors (when equipped) through the
relay output circuit only when the rear window
defogger relay coil is energized.
²The normally closed terminal (87A) is not con-
nected to any circuit in this application, but provides
a battery current output only when the rear window
defogger relay coil is de-energized.
The rear window defogger relay cannot be repaired
and, if faulty or damaged, it must be replaced. Refer
to the appropriate wiring information for diagnosis
and testing of the micro-relay and for complete rear
window defogger system wiring diagrams.
REMOVAL
(1)Disconnect and isolate the negative battery cable.
(2) Remove the cover from the integrated power
module (IPM) (Fig. 3).
(3) Refer to the fuse and relay layout map on the
inner surface of the IPM cover for rear window defog-
ger relay identification and location.
(4) Remove the rear window defogger relay from
the IPM.
Fig. 2 Rear Window Defogger Relay
1 - RELAY TERMINALS
2 - RELAY CAVITIES
Fig. 3 Integrated Power Module (IPM)
1 - BATTERY
2 - INTEGRATED POWER MODULE (IPM)
DRHEATED GLASS 8G - 3
REAR WINDOW DEFOGGER RELAY (Continued)

OPERATION
The heated seat module receives fused battery cur-
rent through the Integrated Power Module. The
heated seat switches receive battery current from the
Cab Compartment Node (CCN) only when the igni-
tion switch is in the On position and the engine is
running. The heated seat module shares a common
ground circuit with each of the heated seat elements.
The heated seat system will control the surface tem-
perature of the seat cushion to within the designed
temperature set points of the system.
The heated seat system will also automatically
turn off whenever the ignition switch is turned to
any position except On, or if the engine quits run-
ning. If the ignition switch is turned to the Off posi-
tion or if the engine quits running while a heated
seat is ON, the heated seat will remain Off after the
engine is restarted until a heated seat switch is
depressed again. This helps prevent the vehicles bat-
tery from being drained by the heated seat system.
The heated seat module monitors inputs from the
heated seat sensors and the heated seat switches. Inresponse to these inputs the heated seat module uses
its internal programming to control 12v to the heated
seat elements in both front seats and to control the
heated seat LED indicator lamps located in both of
the heated seat switches. The heated seat module is
also programmed to provide self-diagnostics, if a
problem with the heated seat system is detected. If
the module detects certain failures within the heated
seat system, it will provide a visual indication of the
failure by flashing the indicator lamps in the appro-
priate heated seat switch. The heated seat module
will automatically turn off the heated seat elements
if it detects a short or open in the heated seat ele-
ment circuit or a heated seat sensor value that is out
of range.
DIAGNOSIS AND TESTING - HEATED SEAT
SYSTEM
HEATED SEAT SYSTEM SELF-DIAGNOSIS
The heated seat system is capable of performing
some self-diagnostics. The following table depicts the
various monitored failures which will be reported to
the vehicle operator or technician by flashing the
individual heated seat switch Light Emitting Diode
(LED) indicator lamps. Refer to the HEATED SEAT
SYSTEM SELF-DIAGNOSIS table for failure identi-
fication. The drivers heated seat switch indicator
lamps will flash if a failure occurs in the driver
heated seat, and the passengers heated seat switch
indicator lamps will flash for a passenger heated seat
failure. If a monitored heated seat system failure
occurs, the switch indicator lamps will flash at a
pulse rate of about one-half second on, followed by
about one-half second off for a duration of about one
minute after the switch for the faulty heated seat is
depressed in either the Low or High direction. This
process will repeat every time the faulty heated seat
switch is actuated until the problem has been cor-
rected.
HEATED SEAT SYSTEM SELF-DIAGNOSIS
Monitored FailureSwitch High
Indicator LampSwitch Low
Indicator Lamp
Heated Seat
Element ShortedFlashing Flashing
Heated Seat
Element OpenFlashing Off
Heated Seat
Sensor Value Out
of RangeOff Flashing
Diagnostic logic is built into the heated seat mod-
ule to help the person trying to locate the problem by
the most efficient means possible. Anytime a problem
Fig. 1 DR Heated Seat System Diagram
1 - WIRE HARNESS
2 - DRIVER HEATED SEAT SWITCH
3 - PASSENGER HEATED SEAT SWITCH
4 - PASSENGER HEATED SEAT CUSHION ELEMENT
5 - SEAT CUSHION/BACK ELEMENT ELECTRICAL CONNECTOR
LOCATION
6 - DRIVER HEATED SEAT BACK ELEMENT
7 - DRIVER HEATED SEAT CUSHION ELEMENT
8 - HEATED SEAT MODULE
8G - 8 HEATED SEAT SYSTEMDR
HEATED SEAT SYSTEM (Continued)

dimmer controlled back lighting of the switch when
the headlamps or park lamps are on.
The heated seat switches are both mounted in the
instrument panel center bezel, located in the lower
center of the instrument panel. The two switches are
snapped into the mounting holes of the heated seat
switch bezel, and the heated seat switch bezel is
secured with screws to the instrument panel center
bezel. The heated seat switches are differentiated by
the keyway in the connector receptacle on the backs
of the switches and keyway on the switch housing.
The instrument panel wire harness connectors for
the heated seat switches are keyed to match the con-
nector receptacles on the switches so that the two
heated seat switches can only be connected to the
proper heated seat electrical.
The two LED indicator lamps and the incandescent
bulb in each heated seat switch cannot be repaired. If
the indicator lamps or back lighting bulb are faulty
or damaged, the individual heated seat switch must
be replaced.
OPERATION
The heated seat switches receive battery current
through a fused ignition switch output (run) circuit
when the ignition switch is in the On position.
Depressing the heated seat switch rocker to its
momentary High or Low position provides a hard-
wired resistance signal to the heated seat module.
This signal tells the module to energize the heatedseat element of the selected seat and maintain the
requested temperature setting. If the heated seat
switch is depressed to a different position (Low or
High) than the currently selected state, the heated
seat module will change states to support the new
selection. If a heated seat switch is depressed a sec-
ond time, the heated seat module interprets the sec-
ond input as a request to turn the seat heater OFF.
The High and Low LED indicator lamps in the
heated seat switches receive battery current through
a fused ignition switch output (run) circuit when the
ignition switch is in the On position. The ground side
of each indicator lamp is controlled by the heated
seat module. This control of the switch indicator
lamps also allows the module to provide diagnostic
feedback to the vehicle operator or technician to indi-
cate heated seat system faults by flashing the indica-
tor lamps on and off. One side of the incandescent
back lighting bulb in each heated seat switch is con-
nected to ground at all times. The other side of the
incandescent bulb is connected to the fused panel
lamps dimmer switch signal circuit. These bulbs are
energized when the park lamps or headlamps are
turned on, and their illumination intensity is con-
trolled by the panel lamps dimmer switch.
DIAGNOSIS AND TESTING - HEATED SEAT
SWITCH
Refer toWiring Diagramsfor connector pin-outs
and the location of complete heated seat system wir-
ing diagrams.
WARNING: DISABLE THE AIRBAG SYSTEM
BEFORE ATTEMPTING ANY STEERING WHEEL,
STEERING COLUMN, OR INSTRUMENT PANEL
COMPONENT DIAGNOSIS OR SERVICE. DISCON-
NECT AND ISOLATE THE BATTERY NEGATIVE
(GROUND) CABLE, THEN WAIT TWO MINUTES FOR
THE AIRBAG SYSTEM CAPACITOR TO DISCHARGE
BEFORE PERFORMING FURTHER DIAGNOSIS OR
SERVICE. THIS IS THE ONLY SURE WAY TO DIS-
ABLE THE AIRBAG SYSTEM. FAILURE TO TAKE
THE PROPER PRECAUTIONS COULD RESULT IN
ACCIDENTAL AIRBAG DEPLOYMENT AND POSSI-
BLE PERSONAL INJURY.
(1) If the problem being diagnosed involves inoper-
ative heated seat switch back lighting and the cluster
illumination lamps operate, go to Step 2. If the prob-
lem being diagnosed involves inoperative heated seat
switch back lighting and the cluster illumination
lamps are also inoperative, (Refer to 8 - ELECTRI-
CAL/INSTRUMENT CLUSTER - DIAGNOSIS AND
TESTING). If the problem being diagnosed involves
inoperative heated seat switch indicator lamps and
the heated seat elements do not heat, proceed. If the
Fig. 4 HEATED SEAT SWITCH
1 - HEATED SEAT SWITCH
2 - LIGHT-EMITTING DIODE (LED) INDICATOR LAMPS
8G - 12 HEATED SEAT SYSTEMDR
HEATED SEAT SWITCH (Continued)

The heated seat module is an electronic micropro-
cessor controlled device designed and programmed to
use inputs from the battery, the two heated seat
switches and the two heated seat sensors to operate
and control the heated seat elements in both front
seats and the two heated seat indicator lamp Light-
Emitting Diodes (LEDs) in each heated seat switch.
The heated seat module is also programmed to per-
form self-diagnosis of certain heated seat system
functions and provide feedback of that diagnosis
through the heated seat switch indicator lamps.
The heated seat module cannot be repaired. If the
heated seat module is damaged or faulty, the entire
module must be replaced.
OPERATION
The heated seat module operates on fused battery
current received from the integrated power module.
Inputs to the module include a resistor multiplexed
heated seat switch request circuit for each of the two
heated seat switches and the heated seat sensor
inputs from the seat cushions of each front seat. In
response to those inputs the heated seat module con-
trols battery current feeds to the heated seat ele-
ments and sensors, and controls the ground for the
heated seat switch indicator lamps.
When a heated seat switch (Driver or Passenger) is
depressed a signal is received by the heated seat
module, the module energizes the proper indicator
LED (Low or High) in the switch by grounding the
indicator lamp circuit to indicate that the heated seat
system is operating. At the same time, the heated
seat module energizes the selected heated seat sensor
circuit and the sensor provides the module with an
input indicating the surface temperature of the
selected seat cushion.The Low heat set point is about 36É C (96.8É F),
and the High heat set point is about 42É C (107.6É F).
If the seat cushion surface temperature input is
below the temperature set point for the selected tem-
perature setting, the heated seat module energizes
an N-channel Field Effect Transistor (N-FET) within
the module which energizes the heated seat elements
in the selected seat cushion and back. When the sen-
sor input to the module indicates the correct temper-
ature set point has been achieved, the module
de-energizes the N-FET which de-energizes the
heated seat elements. The heated seat module will
continue to cycle the N-FET as needed to maintain
the selected temperature set point.
If the heated seat module detects a heated seat
sensor value input that is out of range or a shorted
or open heated seat element circuit, it will notify the
vehicle operator or the repair technician of this con-
dition by flashing the High and/or Low indicator
lamps in the affected heated seat switch. Refer to
Diagnosis and Testing Heated Seat Systemin
Heated Systems for flashing LED diagnosis and test-
ing procedures. Refer toDiagnosis and Testing
Heated Seat Modulein this section for heated seat
module diagnosis and testing procedures.
DIAGNOSIS AND TESTING - HEATED SEAT
MODULE
If a heated seat fails to heat and one or both of the
indicator lamps on a heated seat switch flash, refer
toDiagnosis and Testing Heated Seat Systemin
Heated Seats for the location of flashing LED heated
seat system diagnosis and testing procedures. If a
heated seat heats but one or both indicator lamps on
the heated seat switch fail to operate, test the heated
seat switch. Refer toDiagnosis and Testing
Heated Seat Switchin Heated Seats for heated
seat switch diagnosis and testing procedures. If the
heated seat switch checks OK, proceed as follows.
(1) Check the heated seat element (Refer to 8 -
ELECTRICAL/HEATED SEATS/HEATED SEAT
ELEMENT - DIAGNOSIS AND TESTING).
(2) Check the heated seat sensor (Refer to 8 -
ELECTRICAL/HEATED SEATS/HEATED SEAT
SENSOR - DIAGNOSIS AND TESTING).
(3) Check the heated seat switch (Refer to 8 -
ELECTRICAL/HEATED SEATS/DRIVER HEATED
SEAT SWITCH - DIAGNOSIS AND TESTING).
NOTE: Refer to Wiring for the location of complete
heated seat system wiring diagrams and connector
pin-out information.
(4) Using a voltmeter, backprobe the appropriate
heated seat module connector, do not disconnect.
Check for voltage at the appropriate pin cavities. 12v
Fig. 5 Heated Seat Module
1 - MOUNTING TABS (NOT USED ON DR)
2 - HEATED SEAT MODULE
3 - ELECTRICAL CONNECTOR RECEPTACLE
8G - 14 HEATED SEAT SYSTEMDR
HEATED SEAT MODULE (Continued)

NOTE: Certain indicators in this instrument cluster
are automatically configured. This feature allows
those indicators to be activated or deactivated for
compatibility with certain optional equipment. If the
problem being diagnosed involves improper illumi-
nation of the cruise indicator, the electronic throttle
control indicator, the service four-wheel drive indi-
cator, the tow/haul indicator, the transmission over-
temp indicator, the upshift indicator, the security
indicator or the gear selector indicator, disconnect
and isolate the battery negative cable. After about
five minutes, reconnect the battery negative cable
and turn the ignition switch to the On position. The
instrument cluster should automatically relearn the
equipment in the vehicle and properly configure the
configurable indicators accordingly.
ABS INDICATOR
DESCRIPTION
An Antilock Brake System (ABS) indicator is stan-
dard equipment on all instrument clusters (Fig. 8).
However, the instrument cluster can be programmed
to disable this indicator on vehicles that are not
equipped with the ABS or Rear Wheel Anti-Lock
(RWAL) brake systems, which are not available in
some markets. On vehicles equipped with a gasoline
engine, the ABS indicator is located near the lower
edge of the instrument cluster, between the tachom-
eter and the speedometer. On vehicles equipped with
a diesel engine, the ABS indicator is located on the
right side of the instrument cluster, to the right of
the engine temperature gauge. The ABS indicator
consists of a stencil-like cutout of the International
Control and Display Symbol icon for ªFailure of Anti-
lock Braking Systemº in the opaque layer of the
instrument cluster overlay. The dark outer layer of
the overlay prevents the indicator from being clearly
visible when it is not illuminated. An amber Light
Emitting Diode (LED) behind the cutout in the
opaque layer of the overlay causes the icon to appear
in amber through the translucent outer layer of the
overlay when the indicator is illuminated from
behind by the LED, which is soldered onto the
instrument cluster electronic circuit board. The ABS
indicator is serviced as a unit with the instrument
cluster.
OPERATION
The ABS indicator gives an indication to the vehi-
cle operator when the ABS system is faulty or inop-
erative. This indicator is controlled by a transistor on
the instrument cluster circuit board based upon clus-
ter programming and electronic messages received by
the cluster from the Controller Antilock Brake (CAB)
over the Programmable Communications Interface
(PCI) data bus. The ABS indicator Light Emitting
Diode (LED) is completely controlled by the instru-
ment cluster logic circuit, and that logic will only
allow this indicator to operate when the instrument
cluster receives a battery current input on the fused
ignition switch output (run-start) circuit. Therefore,
the LED will always be off when the ignition switch
is in any position except On or Start. The LED only
illuminates when it is provided a path to ground by
the instrument cluster transistor. The instrument
cluster will turn on the ABS indicator for the follow-
ing reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the ABS indicator is illu-
minated by the cluster for about two seconds as a
bulb test.
²ABS Lamp-On Message- Each time the clus-
ter receives a lamp-on message from the CAB, the
ABS indicator will be illuminated. The indicator
remains illuminated until the cluster receives a
lamp-off message from the CAB, or until the ignition
switch is turned to the Off position, whichever occurs
first.
²Communication Error- If the cluster receives
no lamp-on or lamp-off messages from the CAB for
three consecutive seconds, the ABS indicator is illu-
minated. The indicator remains illuminated until the
cluster receives a valid message from the CAB, or
until the ignition switch is turned to the Off position,
whichever occurs first.
²Actuator Test- Each time the instrument clus-
ter is put through the actuator test, the ABS indica-
tor will be turned on, then off again during the bulb
check portion of the test to confirm the functionality
of the LED and the cluster control circuitry.
²ABS Diagnostic Test- The ABS indicator is
blinked on and off by lamp-on and lamp-off messages
from the CAB during the performance of the ABS
diagnostic tests.
The CAB continually monitors the ABS circuits
and sensors to decide whether the system is in good
operating condition. The CAB then sends the proper
lamp-on or lamp-off messages to the instrument clus-
ter. If the CAB sends a lamp-on message after the
bulb test, it indicates that the CAB has detected a
system malfunction and/or that the ABS system has
become inoperative. The CAB will store a Diagnostic
Trouble Code (DTC) for any malfunction it detects.
Fig. 8 ABS Indicator
DRINSTRUMENT CLUSTER 8J - 17
INSTRUMENT CLUSTER (Continued)

Each time the ABS indicator fails to light due to an
open or short in the cluster ABS indicator circuit, the
cluster sends a message notifying the CAB of the
condition, then the instrument cluster and the CAB
will each store a DTC. For proper diagnosis of the
antilock brake system, the CAB, the PCI data bus, or
the electronic message inputs to the instrument clus-
ter that control the ABS indicator, a DRBIIItscan
tool is required. Refer to the appropriate diagnostic
information.
AIRBAG INDICATOR
DESCRIPTION
An airbag indicator is standard equipment on all
instrument clusters (Fig. 9). However, the instrument
cluster can be programmed to disable this indicator
on vehicles that are not equipped with the airbag
system, which is not available in some markets. The
airbag indicator is located near the upper edge of the
instrument cluster, between the tachometer and the
speedometer. The airbag indicator consists of a sten-
cil-like cutout of the words ªAIR BAGº in the opaque
layer of the instrument cluster overlay. The dark
outer layer of the overlay prevents the indicator from
being clearly visible when it is not illuminated. A red
Light Emitting Diode (LED) behind the cutout in the
opaque layer of the overlay causes the ªAIR BAGº
text to appear in red through the translucent outer
layer of the overlay when the indicator is illuminated
from behind by the LED, which is soldered onto the
instrument cluster electronic circuit board. The air-
bag indicator is serviced as a unit with the instru-
ment cluster.
OPERATION
The airbag indicator gives an indication to the
vehicle operator when the airbag system is faulty or
inoperative. The airbag indicator is controlled by a
transistor on the instrument cluster circuit board
based upon cluster programming and electronic mes-
sages received by the cluster from the Airbag Control
Module (ACM) over the Programmable Communica-
tions Interface (PCI) data bus. The airbag indicator
Light Emitting Diode (LED) is completely controlled
by the instrument cluster logic circuit, and that logic
will only allow this indicator to operate when the
instrument cluster receives a battery current input
on the fused ignition switch output (run-start) cir-
cuit. Therefore, the LED will always be off when theignition switch is in any position except On or Start.
The LED only illuminates when it is provided a path
to ground by the instrument cluster transistor. The
instrument cluster will turn on the airbag indicator
for the following reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the airbag indicator is illu-
minated for about six seconds. The entire six second
bulb test is a function of the ACM.
²ACM Lamp-On Message- Each time the clus-
ter receives a lamp-on message from the ACM, the
airbag indicator will be illuminated. The indicator
remains illuminated for about twelve seconds or until
the cluster receives a lamp-off message from the
ACM, whichever is longer.
²Communication Error- If the cluster receives
no airbag messages for three consecutive seconds, the
airbag indicator is illuminated. The indicator
remains illuminated until the cluster receives a sin-
gle lamp-off message from the ACM.
²Actuator Test- Each time the cluster is put
through the actuator test, the airbag indicator will be
turned on, then off again during the bulb check por-
tion of the test to confirm the functionality of the
LED and the cluster control circuitry. The actuator
test illumination of the airbag indicator is a function
of the instrument cluster.
The ACM continually monitors the airbag system
circuits and sensors to decide whether the system is
in good operating condition. The ACM then sends the
proper lamp-on or lamp-off messages to the instru-
ment cluster. If the ACM sends a lamp-on message
after the bulb test, it indicates that the ACM has
detected a system malfunction and/or that the air-
bags and seat belt tensioners may not deploy when
required, or may deploy when not required. The ACM
will store a Diagnostic Trouble Code (DTC) for any
malfunction it detects. Each time the airbag indicator
fails to illuminate due to an open or short in the
cluster airbag indicator circuit, the cluster sends a
message notifying the ACM of the condition, the
instrument cluster and the ACM will each store a
DTC, and the cluster will flash the seatbelt indicator
on and off as a backup to notify the vehicle operator.
For proper diagnosis of the airbag system, the ACM,
the PCI data bus, or the electronic message inputs to
the instrument cluster that control the airbag indica-
tor, a DRBIIItscan tool is required. Refer to the
appropriate diagnostic information.
Fig. 9 Airbag Indicator
8J - 18 INSTRUMENT CLUSTERDR
ABS INDICATOR (Continued)

BRAKE/PARK BRAKE
INDICATOR
DESCRIPTION
A brake indicator is standard equipment on all
instrument clusters (Fig. 10). The brake indicator is
located near the lower edge of the instrument cluster,
between the tachometer and the speedometer. The
brake indicator consists of stencil-like cutouts of the
word ªBRAKEº and the International Control and
Display Symbol icon for ªBrake Failureº in the
opaque layer of the instrument cluster overlay. The
dark outer layer of the overlay prevents the indicator
from being clearly visible when it is not illuminated.
A red Light Emitting Diode (LED) behind the cutout
in the opaque layer of the overlay causes the
ªBRAKEº text and the icon to appear in red through
the translucent outer layer of the overlay when the
indicator is illuminated from behind by the LED,
which is soldered onto the instrument cluster elec-
tronic circuit board. The brake indicator is serviced
as a unit with the instrument cluster.
OPERATION
The brake indicator gives an indication to the vehi-
cle operator when the parking brake is applied, when
there are certain brake hydraulic system malfunc-
tions as indicated by a low brake hydraulic fluid level
condition, or when the brake fluid level switch is dis-
connected. The brake indicator can also give an indi-
cation when certain faults are detected in the
Antilock Brake System (ABS). This indicator is con-
trolled by a transistor on the instrument cluster cir-
cuit board based upon cluster programming,
electronic messages received by the cluster from the
Controller Antilock Brake (CAB) over the Program-
mable Communications Interface (PCI) data bus, and
a hard wired input from the park brake switch. The
brake indicator Light Emitting Diode (LED) is com-
pletely controlled by the instrument cluster logic cir-
cuit, and that logic will only allow this indicator to
operate when the instrument cluster receives a bat-
tery current input on the fused ignition switch out-
put (run-start) circuit. Therefore, the LED will
always be off when the ignition switch is in any posi-
tion except On or Start. The LED only illuminates
when it is provided a path to ground by the instru-
ment cluster transistor. The instrument cluster will
turn on the brake indicator for the following reasons:²Bulb Test- Each time the ignition switch is
turned to the On position the brake indicator is illu-
minated by the instrument cluster for about two sec-
onds as a bulb test.
²Brake Lamp-On Message- Each time the
cluster receives a lamp-on message from the CAB,
the brake indicator will be illuminated. The CAB can
also send brake lamp-on messages as feedback dur-
ing ABS diagnostic procedures. The indicator
remains illuminated until the cluster receives a
lamp-off message from the CAB, or until the ignition
switch is turned to the Off position, whichever occurs
first.
²Park Brake Switch Input- Each time the
cluster detects ground on the park brake switch
sense circuit (park brake switch closed = park brake
applied or not fully released) while the ignition
switch is in the On position, the brake indicator
flashes on and off. The indicator continues to flash
until the park brake switch sense input to the cluster
is an open circuit (park brake switch open = park
brake fully released), or until the ignition switch is
turned to the Off position, whichever occurs first.
²Actuator Test- Each time the instrument clus-
ter is put through the actuator test, the brake indi-
cator will be turned on, then off again during the
bulb check portion of the test to confirm the function-
ality of the LED and the cluster control circuitry.
The park brake switch on the park brake pedal
mechanism provides a hard wired ground input to
the instrument cluster circuitry through the park
brake switch sense circuit whenever the park brake
is applied or not fully released. The CAB continually
monitors the ABS system circuits and sensors,
including the brake fluid level switch on the brake
master cylinder reservoir, to decide whether the sys-
tem is in good operating condition. The CAB then
sends the proper lamp-on or lamp-off messages to the
instrument cluster. If the CAB sends a lamp-on mes-
sage after the bulb test, it indicates that the CAB
has detected a brake hydraulic system malfunction
and/or that the ABS system has become inoperative.
The CAB will store a Diagnostic Trouble Code (DTC)
for any malfunction it detects.
For further diagnosis of the brake indicator or the
instrument cluster circuitry that controls the LED,
(Refer to 8 - ELECTRICAL/INSTRUMENT CLUS-
TER - DIAGNOSIS AND TESTING). The park brake
switch input to the instrument cluster can be diag-
nosed using conventional diagnostic tools and meth-
ods. For proper diagnosis of the brake fluid level
switch, the ABS, the CAB, the PCI data bus, or the
electronic message inputs to the instrument cluster
that control the brake indicator, a DRBIIItscan tool
is required. Refer to the appropriate diagnostic infor-
mation.
Fig. 10 Brake Indicator
DRINSTRUMENT CLUSTER 8J - 19

cluster programming, a hard wired multiplex input
received by the cluster from the headlamp panel
lamps dimmer switch on the headlamp dimmer
switch mux circuit, and electronic unlock request
messages received from the optional Remote Keyless
Entry (RKE) receiver module. The cargo lamp indica-
tor Light Emitting Diode (LED) is completely con-
trolled by the instrument cluster logic circuit, and
that logic will allow only this indicator to operate
whenever the instrument cluster receives a battery
current input on the fused ignition switch output
(run-start) circuit. Therefore, the LED will always be
off when the ignition switch is in any position except
On or Start. The LED only illuminates when it is
provided a path to ground by the instrument cluster
transistor. The instrument cluster will turn on the
cargo lamp indicator for the following reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the cargo lamp indicator is
illuminated for about two seconds as a bulb test.
²Cargo Lamp-On Input- Each time the cluster
detects a cargo lamp-on input from the headlamp
switch on the headlamp dimmer switch mux circuit,
the cargo lamp and the cargo lamp indicator will be
illuminated. The cargo lamp and indicator remain
illuminated until the cluster receives a cargo lamp-off
input from the headlamp switch, or until the ignition
switch is turned to the Off position, whichever occurs
first.
²Actuator Test- Each time the cluster is put
through the actuator test, the cargo lamp indicator
will be turned on, then off again during the bulb
check portion of the test to confirm the functionality
of the LED and the cluster control circuitry.
The instrument cluster continually monitors the
headlamp dimmer switch circuit to determine the
proper interior lamps features and panel lamps illu-
mination levels to provide. The cluster then energizes
and de-energizes a low side driver circuit to control
the exterior cargo lamp. Each time the instrument
cluster energizes the cargo lamp driver and the igni-
tion switch is in the On or start positions, the cluster
also turns on the cargo lamp indicator. For further
diagnosis of the cargo lamp indicator or the instru-
ment cluster circuitry that controls the indicator,
(Refer to 8 - ELECTRICAL/INSTRUMENT CLUS-
TER - DIAGNOSIS AND TESTING). For proper
diagnosis of the cargo lamp or the headlamp switch
inputs to the instrument cluster that control the
cargo lamp indicator, a DRBIIItscan tool is required.
Refer to the appropriate diagnostic information.CHECK GAUGES INDICATOR
DESCRIPTION
A check gauges indicator is standard equipment on
all instrument clusters (Fig. 12). On vehicles
equipped with a gasoline engine, the check gauges
indicator is located near the lower edge of the instru-
ment cluster, between the tachometer and the speed-
ometer. On vehicles equipped with a diesel engine,
the check gauges indicator is located on the left side
of the instrument cluster, to the left of the voltage
gauge. The check gauges indicator consists of a sten-
cil-like cutout of the words ªCHECK GAGESº in the
opaque layer of the instrument cluster overlay. The
dark outer layer of the overlay prevents the indicator
from being clearly visible when it is not illuminated.
A red Light Emitting Diode (LED) behind the cutout
in the opaque layer of the overlay causes the
ªCHECK GAGESº text to appear in red through the
translucent outer layer of the overlay when the indi-
cator is illuminated from behind by the LED, which
is soldered onto the instrument cluster electronic cir-
cuit board. The check gauges indicator is serviced as
a unit with the instrument cluster.
OPERATION
The check gauges indicator gives an indication to
the vehicle operator when certain instrument cluster
gauge readings reflect a condition requiring immedi-
ate attention. This indicator is controlled by a tran-
sistor on the instrument cluster circuit board based
upon cluster programming and electronic messages
received by the cluster from the Powertrain Control
Module (PCM) on vehicles equipped with a gasoline
engine, or from the Engine Control Module (ECM) on
vehicles equipped with a diesel engine over the Pro-
grammable Communications Interface (PCI) data
bus. The check gauges indicator Light Emitting
Diode (LED) is completely controlled by the instru-
ment cluster logic circuit, and that logic will only
allow this indicator to operate when the instrument
cluster receives a battery current input on the fused
ignition switch output (run-start) circuit. Therefore,
the LED will always be off when the ignition switch
is in any position except On or Start. The LED only
illuminates when it is provided a path to ground by
the instrument cluster transistor. The instrument
cluster will turn on the check gauges indicator for
the following reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the check gauges indicator
is illuminated for about two seconds as a bulb test.
Fig. 12 Check Gauges Indicator
DRINSTRUMENT CLUSTER 8J - 21
CARGO LAMP INDICATOR (Continued)