2002 JEEP LIBERTY Powertrain control

AUTO SHUT DOWN RELAY
DESCRIPTION - PCM OUTPUT
The 5±pin, 12±volt, Automatic Shutdown (ASD)
relay is located in the Power Distribution Center
(PDC). Refer to label on PDC cover for relay location.
OPERATION
OPERATION - ASD SENSE - PCM INPUT
A 12 volt signal at this input indicates to the PCM
that the ASD has been activated. The relay is used to
connect the oxygen sensor heater elements, oxygen
sensor heater relay, ignition coil and fuel injectors to
12 volt + power supply.
This input is used only to sense that the ASD relay
is energized. If the Powertrain Control Module
(PCM) does not see 12 volts at this input when the
ASD should be activated, it will set a Diagnostic
Trouble Code (DTC).
OPERATION - PCM OUTPUT
The ASD relay supplies battery voltage (12+ volts)
to the fuel injectors and ignition coil(s). With certain
emissions packages it also supplies 12±volts to the
oxygen sensor heating elements and the oxygen sen-
sor heater relay.
The ground circuit for the coil within the ASD
relay is controlled by the Powertrain Control Module
(PCM). The PCM operates the ASD relay by switch-
ing its ground circuit on and off.
The ASD relay will be shut±down, meaning the
12±volt power supply to the ASD relay will be de-ac-
tivated by the PCM if the ignition key is left in the
ON position. This is if the engine has not been run-
ning for approximately 1.8 seconds.
DIAGNOSIS AND TESTING - ASD AND FUEL
PUMP RELAYS
The following description of operation and
tests apply only to the Automatic Shutdown
(ASD) and fuel pump relays. The terminals on the
bottom of each relay are numbered. Two different
types of relays may be used, (Fig. 2) or (Fig. 3).
²Terminal number 30 is connected to battery volt-
age. For both the ASD and fuel pump relays, termi-
nal 30 is connected to battery voltage at all times.
²The PCM grounds the coil side of the relay
through terminal number 85.
²Terminal number 86 supplies voltage to the coil
side of the relay.
²When the PCM de-energizes the ASD and fuel
pump relays, terminal number 87A connects to termi-
nal 30. This is the Off position. In the off position,voltage is not supplied to the rest of the circuit. Ter-
minal 87A is the center terminal on the relay.
²When the PCM energizes the ASD and fuel
pump relays, terminal 87 connects to terminal 30.
This is the On position. Terminal 87 supplies voltage
to the rest of the circuit.
The following procedure applies to the ASD and
fuel pump relays.
(1) Remove relay from connector before testing.
(2) With the relay removed from the vehicle, use
an ohmmeter to check the resistance between termi-
nals 85 and 86. The resistance should be 75 ohms +/-
5 ohms.
(3) Connect the ohmmeter between terminals 30
and 87A. The ohmmeter should show continuity
between terminals 30 and 87A.
Fig. 2 TYPE 1 RELAY (ISO MICRO RELAY)
Fig. 3 ASD AND FUEL PUMP RELAY TERMINALSÐ
TYPE 2
TERMINAL LEGEND
NUMBER IDENTIFICATION
30 COMMON FEED
85 COIL GROUND
86 COIL BATTERY
87 NORMALLY OPEN
87A NORMALLY CLOSED
8I - 4 IGNITION CONTROLKJ

cylinders 1 and 4, and coil number two fires cylinders
2 and 3.
The Auto Shutdown (ASD) relay provides battery
voltage to the ignition coil. The PCM provides a
ground contact (circuit) for energizing the coil(s). The
PCM will de-energize the ASD relay if it does not
receive the crankshaft position sensor and camshaft
position sensor inputs.
Base ignition timing is not adjustable.By con-
trolling the coil ground circuit, the PCM is able to set
the base timing and adjust the ignition timing
advance. This is done to meet changing engine oper-
ating conditions.
The ignition coil is not oil filled. The windings are
embedded in an epoxy compound. This provides heat
and vibration resistance that allows the ignition coil
to be mounted on the engine.
Spark plug cables (secondary wires or cables) are
used with the 2.4L engine.
3.7L
Battery voltage is supplied to the 6 ignition coils
from the ASD relay. The Powertrain Control Module
(PCM) opens and closes each ignition coil ground cir-
cuit at a determined time for ignition coil operation.
Base ignition timing is not adjustable.By con-
trolling the coil ground circuit, the PCM is able to set
the base timing and adjust the ignition timing
advance. This is done to meet changing engine oper-
ating conditions.
The ignition coil is not oil filled. The windings are
embedded in an epoxy compound. This provides heat
and vibration resistance that allows the ignition coil
to be mounted on the engine.
Because of coil design, spark plug cables (second-
ary cables) are not used with the 3.7L engine.
REMOVAL
2.4L
(1) Disconnect electrical connector at rear of coil.
(2) Remove all secondary cables from coil.
(3) Remove 4 coil mounting bolts (Fig. 17).
(4) Remove coil from vehicle.
3.7L
An individual ignition coil is used for each spark
plug (Fig. 19). The coil fits into machined holes in the
cylinder head. A mounting stud/nut secures each coil
to the top of the intake manifold (Fig. 18). The bot-
tom of the coil is equipped with a rubber boot to seal
the spark plug to the coil. Inside each rubber boot is
a spring. The spring is used for a mechanical contact
between the coil and the top of the spark plug. These
rubber boots and springs are a permanent part of the
coil and are not serviced separately. An o-ring (Fig.19) is used to seal the coil at the opening into the cyl-
inder head.
(1) Depending on which coil is being removed, the
throttle body air intake tube or intake box may need
to be removed to gain access to coil.
(2) Disconnect electrical connector from coil by
pushing downward on release lock on top of connec-
tor and pull connector from coil.
(3) Clean area at base of coil with compressed air
before removal.
(4) Remove coil mounting nut from mounting stud
(Fig. 18).
(5) Carefully pull up coil from cylinder head open-
ing with a slight twisting action.
(6) Remove coil from vehicle.
INSTALLATION
2.4L
(1) Position coil to engine.
(2) Install 4 mounting bolts. Refer to torque speci-
fications.
(3) Install secondary cables.
(4) Install electrical connector at rear of coil.
(5) Install air cleaner tube and housing.
3.7L
(1) Using compressed air, blow out any dirt or con-
taminants from around top of spark plug.
(2) Check condition of coil o-ring and replace as
necessary. To aid in coil installation, apply silicone to
coil o-ring.
Fig. 17 IGNITION COIL - 2.4L
1 - IGNITION COIL
2 - MOUNTING BOLTS (4)
8I - 10 IGNITION CONTROLKJ
IGNITION COIL (Continued)

(3) Position ignition coil into cylinder head opening
and push onto spark plug. Do this while guiding coil
base over mounting stud.
(4) Install coil mounting stud nut. Refer to torque
specifications.(5) Connect electrical connector to coil by snapping
into position.
(6) If necessary, install throttle body air tube or
box.
KNOCK SENSOR
DESCRIPTION
The 2 knock sensors are bolted into the cylinder
block under the intake manifold. The sensors are
used only with the 3.7L engine.
OPERATION
Two knock sensors are used on the 3.7L V-6
engine; one for each cylinder bank. When the knock
sensor detects a knock in one of the cylinders on the
corresponding bank, it sends an input signal to the
Powertrain Control Module (PCM). In response, the
PCM retards ignition timing for all cylinders by a
scheduled amount.
Knock sensors contain a piezoelectric material
which constantly vibrates and sends an input voltage
(signal) to the PCM while the engine operates. As the
intensity of the crystal's vibration increases, the
knock sensor output voltage also increases.
The voltage signal produced by the knock sensor
increases with the amplitude of vibration. The PCM
receives the knock sensor voltage signal as an input.
If the signal rises above a predetermined level, the
PCM will store that value in memory and retard
ignition timing to reduce engine knock. If the knock
sensor voltage exceeds a preset value, the PCM
retards ignition timing for all cylinders. It is not a
selective cylinder retard.
The PCM ignores knock sensor input during engine
idle conditions. Once the engine speed exceeds a
specified value, knock retard is allowed.
Knock retard uses its own short term and long
term memory program.
Long term memory stores previous detonation
information in its battery-backed RAM. The maxi-
mum authority that long term memory has over tim-
ing retard can be calibrated.
Short term memory is allowed to retard timing up
to a preset amount under all operating conditions (as
long as rpm is above the minimum rpm) except at
Wide Open Throttle (WOT). The PCM, using short
term memory, can respond quickly to retard timing
when engine knock is detected. Short term memory
is lost any time the ignition key is turned off.
Fig. 18 IGNITION COIL LOCATION - 3.7L
1 - IGNITION COIL
2 - COIL MOUNTING NUT
Fig. 19 IGNITION COIL - 3.7L
1 - O-RING
2 - IGNITION COIL
3 - ELECTRICAL CONNECTOR
KJIGNITION CONTROL 8I - 11
IGNITION COIL (Continued)

NOTE: Over or under tightening the sensor mount-
ing bolts will affect knock sensor performance, pos-
sibly causing improper spark control. Always use
the specified torque when installing the knock sen-
sors.
REMOVAL
The 2 knock sensors are bolted into the cylinder
block under the intake manifold (Fig. 20).
NOTE: The left sensor is identified by an identifica-
tion tag (LEFT). It is also identified by a larger bolt
head. The Powertrain Control Module (PCM) must
have and know the correct sensor left/right posi-
tions. Do not mix the sensor locations.
(1) Disconnect knock sensor dual pigtail harness
from engine wiring harness. this connection is made
near rear of left valve cover (Fig. 20).
(2) Remove intake manifold. Refer to Engine sec-
tion.
(3) Remove sensor mounting bolts (Fig. 20). Note
foam strip on bolt threads. This foam is used only to
retain the bolts to sensors for plant assembly. It is
not used as a sealant. Do not apply any adhesive,
sealant or thread locking compound to these bolts.
(4) Remove sensors from engine.
INSTALLATION
NOTE: The left sensor is identified by an identifica-
tion tag (LEFT). It is also identified by a larger bolt
head. The Powertrain Control Module (PCM) must
have and know the correct sensor left/right posi-
tions. Do not mix the sensor locations.
(1) Thoroughly clean knock sensor mounting holes.
(2) Install sensors into cylinder block.
NOTE: Over or under tightening the sensor mount-
ing bolts will affect knock sensor performance, pos-
sibly causing improper spark control. Always use
the specified torque when installing the knock sen-
sors. The torque for the knock senor bolt is rela-
tively light for an 8mm bolt.
NOTE: Note foam strip on bolt threads. This foam is
used only to retain the bolts to sensors for plant
assembly. It is not used as a sealant. Do not apply
any adhesive, sealant or thread locking compound
to these bolts.
(3) Install and tighten mounting bolts. Refer to
torque specification.
(4) Install intake manifold. Refer to Engine sec-
tion.
(5) Connect knock sensor wiring harness to engine
harness at rear of intake manifold.
SPARK PLUG
DESCRIPTION
Resistor type spark plugs are used.
Spark plug resistance values range from 6,000 to
20,000 ohms (when checked with at least a 1000 volt
spark plug tester).Do not use an ohmmeter to
check the resistance values of the spark plugs.
Inaccurate readings will result.
OPERATION
To prevent possible pre-ignition and/or mechanical
engine damage, the correct type/heat range/number
spark plug must be used.
Always use the recommended torque when tighten-
ing spark plugs. This is especially true when plugs
are equipped with tapered seats. Incorrect torque can
distort the spark plug and change plug gap. It can
also pull the plug threads and do possible damage to
both the spark plug and the cylinder head.
Remove the spark plugs and examine them for
burned electrodes and fouled, cracked or broken por-
celain insulators. Keep plugs arranged in the order
in which they were removed from the engine. A sin-
Fig. 20 KNOCK SENSOR LOCATION
1 - KNOCK SENSORS (2)
2 - MOUNTING BOLTS
8I - 12 IGNITION CONTROLKJ
KNOCK SENSOR (Continued)

OPERATION
The ElectroMechanical Instrument Cluster (EMIC)
is designed to allow the vehicle operator to monitor
the conditions of many of the vehicle components and
operating systems. The gauges and indicators in the
EMIC provide valuable information about the various
standard and optional powertrains, fuel and emis-
sions systems, cooling systems, lighting systems,
safety systems and many other convenience items.
The EMIC is installed in the instrument panel so
that all of these monitors can be easily viewed by the
vehicle operator when driving, while still allowing
relative ease of access for service. The microproces-sor-based EMIC hardware and software uses various
inputs to control the gauges and indicators visible on
the face of the cluster. Some of these inputs are hard
wired, but most are in the form of electronic mes-
sages that are transmitted by other electronic mod-
ules over the Programmable Communications
Interface (PCI) data bus network. (Refer to 8 -
ELECTRICAL/ELECTRONIC CONTROL MOD-
ULES/COMMUNICATION - OPERATION).
The EMIC microprocessor smooths the input data
using algorithms to provide gauge readings that are
accurate, stable and responsive to operating condi-
tions. These algorithms are designed to provide
Fig. 2 EMIC Gauges & Indicators
1 - SKIS INDICATOR 16 - REAR FOG LAMP INDICATOR
2 - AIRBAG INDICATOR 17 - ABS INDICATOR
3 - LOW FUEL INDICATOR 18 - CHARGING INDICATOR
4 - WAIT-TO-START INDICATOR 19 - WATER-IN-FUEL INDICATOR
5 - OVERDRIVE-OFF INDICATOR 20 - ENGINE TEMPERATURE GAUGE
6 - COOLANT LOW INDICATOR 21 - ODOMETER/TRIP ODOMETER SWITCH BUTTON
7 - SEATBELT INDICATOR 22 - ODOMETER/TRIP ODOMETER DISPLAY
8 - TACHOMETER 23 - CRUISE INDICATOR
9 - LEFT TURN INDICATOR 24 - LOW OIL PRESSURE INDICATOR
10 - HIGH BEAM INDICATOR 25 - TRANSMISSION OVERTEMP INDICATOR
11 - RIGHT TURN INDICATOR 26 - PART TIME 4WD INDICATOR
12 - SPEEDOMETER 27 - BRAKE INDICATOR
13 - FRONT FOG LAMP INDICATOR 28 - FULL TIME 4WD INDICATOR
14 - 4WD LOW MODE INDICATOR 29 - SECURITY INDICATOR
15 - MALFUNCTION INDICATOR LAMP (MIL) 30 - FUEL GAUGE
8J - 4 INSTRUMENT CLUSTERKJ
INSTRUMENT CLUSTER (Continued)

eter/trip odometer switch button that extends
through the lower edge of the cluster lens, just right
of the speedometer. Actuating this switch momen-
tarily with the ignition switch in the On position will
toggle the VFD between the odometer and trip odom-
eter modes. Depressing the switch button for about
two seconds while the VFD is in the trip odometer
mode will reset the trip odometer value to zero. Hold-
ing this switch depressed while turning the ignition
switch from the Off position to the On position will
initiate the EMIC self-diagnostic actuator test. The
VFD will also display the cluster software version
level near the completion of the EMIC self-diagnostic
actuator test. Refer to the appropriate diagnostic
information for additional details on this VFD func-
tion.
The VFD is diagnosed using the EMIC self-diag-
nostic actuator test. (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND
TESTING). Proper testing of the PCI data bus and
the electronic data bus message inputs to the EMIC
that control some of the VFD functions requires the
use of a DRBIIItscan tool. Refer to the appropriate
diagnostic information. Specific operation details for
the odometer, the trip odometer, and the various
warning message functions of the VFD may be found
elsewhere in this service information.
INDICATORS Indicators are located in various
positions within the EMIC and are all connected to
the EMIC circuit board. The turn signal indicators,
security indicator, washer fluid indicator, and coolant
low indicator (diesel engine only) use hard wired
inputs to the EMIC. The brake indicator is controlled
by PCI data bus messages from the Controller
Antilock Brake (CAB) as well as by hard wired park
brake switch and brake fluid level switch inputs to
the EMIC. The Malfunction Indicator Lamp (MIL) is
normally controlled by PCI data bus messages from
the Powertrain Control Module (PCM); however, if
the EMIC loses PCI data bus communication, the
EMIC circuitry will automatically turn the MIL on
until PCI data bus communication is restored. The
EMIC uses PCI data bus messages from the Body
Control Module (BCM), the PCM, the Airbag Control
Module (ACM), and the CAB to control all of the
remaining indicators.
The various indicators are controlled by different
strategies; some receive fused ignition switch output
from the EMIC circuitry and have a switched ground,
others are grounded through the EMIC circuitry and
have a switched battery feed, while still others are
completely controlled by the EMIC microprocessor
based upon various hard wired and electronic mes-
sage inputs. Some indicators are illuminated at a
fixed intensity, while the illumination intensity ofothers is synchronized with that of the EMIC general
illumination lamps.
In addition, certain indicators in this instrument
cluster are automatically configured or self-config-
ured. This feature allows the configurable indicators
to be enabled by the EMIC circuitry for compatibility
with certain optional equipment. The ABS indicator,
airbag indicator, SKIS indicator are automatically
configured by PCI data bus messages received by the
EMIC from the CAB, ACM, or Sentry Key Immobi-
lizer Module (SKIM) after the EMIC is installed in
the vehicle. Once these configuration settings are
learned by the EMIC, the DRBIIItscan tool must be
used to remove these settings from the EMIC non-
volatile memory. The self-configured indicators
remain latent in each EMIC at all times and will be
activated only when the EMIC receives the appropri-
ate PCI message inputs for the optional system or
equipment.
The hard wired indicators are diagnosed using con-
ventional diagnostic methods. The EMIC and PCI
bus message controlled indicators are diagnosed
using the EMIC self-diagnostic actuator test. (Refer
to 8 - ELECTRICAL/INSTRUMENT CLUSTER -
DIAGNOSIS AND TESTING). Proper testing of the
PCI data bus and the electronic data bus message
inputs to the EMIC that control each indicator
require the use of a DRBIIItscan tool. Refer to the
appropriate diagnostic information. Specific details of
the operation for each indicator may be found else-
where in this service information.
CLUSTER ILLUMINATION The EMIC has several
illumination lamps that are illuminated when the
exterior lighting is turned on with the headlamp
(multi-function) switch. The illumination intensity of
these lamps is adjusted by a 12-volt Pulse Width
Modulated (PWM) output of the EMIC when the
interior lighting control ring on the left control stalk
of the multi-function switch is rotated (down to dim,
up to brighten) to one of six available minor detent
positions. The BCM provides electronic dimming
level messages based upon internal programming
and inputs it receives from the control knob and con-
trol ring on the left (lighting) control stalk of the
multi-function switch on the steering column, then
provides a control output to energize or de-energize
the park lamp relay as appropriate. The energized
park lamp relay provides battery current to the
EMIC on the hard wired fused park lamp relay out-
put circuit, and the BCM provides the electronic dim-
ming level message to the EMIC over the PCI data
bus. The EMIC electronic circuitry provides the
proper PWM output to the cluster illumination lamps
and the VFD on the EMIC circuit board, then pro-
vides a synchronized PWM output on the hard wired
8J - 6 INSTRUMENT CLUSTERKJ
INSTRUMENT CLUSTER (Continued)

fused ignition switch output (run-start) circuit
between the JB and the ignition switch as required.
(6) With the ignition switch still in the On posi-
tion, check for battery voltage at the fused ignition
switch output (run-start) circuit cavity of the instru-
ment panel wire harness connector for the instru-
ment cluster. If OK, go to Step 7. If not OK, repair
the open fused ignition switch output circuit (run-
start) between the instrument cluster and the JB as
required.
(7) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Check for continuity between the ground circuit cav-
ity of the instrument panel wire harness connector
for the instrument cluster and a good ground. There
should be continuity. If OK, refer to ACTUATOR
TEST . If not OK, repair the open ground circuit
between the instrument cluster and ground (G202) as
required.
ACTUATOR TEST
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, SEAT BELT TENSIONER,
FRONT IMPACT SENSORS, SIDE CURTAIN AIRBAG,
OR INSTRUMENT PANEL COMPONENT DIAGNOSIS
OR SERVICE. DISCONNECT AND ISOLATE THE
BATTERY NEGATIVE (GROUND) CABLE, THEN
WAIT TWO MINUTES FOR THE SYSTEM CAPACI-
TOR TO DISCHARGE BEFORE PERFORMING FUR-
THER DIAGNOSIS OR SERVICE. THIS IS THE ONLY
SURE WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
The instrument cluster actuator test will put the
instrument cluster into its self-diagnostic mode. In
this mode the instrument cluster can perform a self-
diagnostic test that will confirm that the instrument
cluster circuitry, the gauges, the PCI data bus mes-
sage controlled indicator lamps, and the chime tone
generator are capable of operating as designed. Dur-
ing the actuator test the instrument cluster circuitry
will sound the chime tone generator, position each of
the gauge needles at various specified calibration
points, illuminate each of the segments in the Vacu-um-Fluorescent Display (VFD), and turn all of the
PCI data bus message-controlled indicators on and
off again.
Successful completion of the actuator test will con-
firm that the instrument cluster is operational. How-
ever, there may still be a problem with the PCI data
bus, the Powertrain Control Module (PCM), the Air-
bag Control Module (ACM), the Sentry Key Immobi-
lizer Module (SKIM), or the inputs to one of these
electronic control modules. Use a DRBIIItscan tool
to diagnose these components. Refer to the appropri-
ate diagnostic information.
(1) Begin the test with the ignition switch in the
Off position.
(2) Depress the odometer/trip odometer switch but-
ton.
(3) While still holding the odometer/trip odometer
switch button depressed, turn the ignition switch to
the On position, but do not start the engine.
(4) Release the odometer/trip odometer switch but-
ton.
(5) The instrument cluster will automatically
begin the actuator test sequence, as follows:
(a) The cluster will turn on, then off again each
of the PCI data bus message controlled indicators
to confirm the functionality of the indicator and
the cluster control circuitry:
(b) The cluster will sweep the needles for each of
the gauges to several calibration points in sequence
to confirm the functionality of the gauge and the
cluster control circuitry:
(c) The cluster will sequentially step the odome-
ter/trip odometer VFD display from all ones
( 111111 )through all nines (999999) to confirm the
functionality of all VFD segments and their control
circuitry, then display the software version number.
(d) The cluster will generate five (5) chime tones
to confirm the functionality of the chime tone gen-
erator and the chime control circuitry.
(6) The actuator test is now completed. The instru-
ment cluster will automatically exit the self-diagnos-
tic mode and return to normal operation at the
completion of the test, if the ignition switch is turned
to the Off position during the test, or if an engine
rpm message indicating that the engine is running is
received from the PCM over the PCI data bus during
the test.
(7) Go back to Step 1 to repeat the test, if
required.
8J - 8 INSTRUMENT CLUSTERKJ
INSTRUMENT CLUSTER (Continued)

tor for the park brake switch from the switch termi-
nal. Check for continuity between the terminal of the
park brake switch and a good ground. There should
be no continuity with the park brake released, and
continuity with the park brake applied. If OK, go to
Step 2. If not OK, replace the faulty park brake
switch.
(2) Disconnect the instrument panel wire harness
connector for the instrument cluster from the cluster
connector receptacle. Check for continuity between
the park brake switch sense circuit cavity of the front
body wire harness connector for the park brake
switch and a good ground. There should be no conti-
nuity. If not OK, repair the shorted park brake
switch sense circuit between the park brake switch
and the instrument cluster as required.
CHARGING INDICATOR
DESCRIPTION
A charging indicator is standard equipment on all
instrument clusters. The charging indicator is located
above the engine temperature gauge and to the right
of the speedometer in the instrument cluster. The
charging indicator consists of a stencil-like cutout of
the International Control and Display Symbol icon
for ªBattery Charging Conditionº 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 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 electronic circuit board. The
charging indicator is serviced as a unit with the
instrument cluster.
OPERATION
The charging indicator gives an indication to the
vehicle operator when the electrical system voltage is
too low or too high. This indicator is controlled by a
transistor on the instrument cluster electronic circuit
board based upon the cluster programming and elec-
tronic messages received by the cluster from the
Powertrain Control Module (PCM) over the Program-
mable Communications Interface (PCI) data bus. The
charging 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 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 charging indicator for the following rea-
sons:
²Bulb Test- Each time the ignition switch is
turned to the On position the charging indicator is
illuminated by the instrument cluster for about three
seconds as a bulb test.
²Charge Fail Message- Each time the cluster
receives a charge fail message from the PCM (system
voltage is nine volts or lower, the charging indicator
will be illuminated. The indicator remains illumi-
nated until the cluster receives a message from the
PCM indicating there is no charge fail condition (sys-
tem voltage is twelve volts or higher, but lower than
sixteen volts), or until the ignition switch is turned to
the Off position, whichever occurs first.
²Voltage High Message- Each time the cluster
receives a message from the PCM indicating a volt-
age high condition (system voltage is sixteen volts or
higher), the lamp will be illuminated. The lamp
remains illuminated until the cluster receives a mes-
sage from the PCM indicating there is no voltage
high condition (system voltage is lower than sixteen
volts, but higher than nine volts), or until the igni-
tion switch is turned to the Off position, whichever
occurs first.
²Actuator Test- Each time the cluster is put
through the actuator test, the charging 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 PCM continually monitors the electrical sys-
tem voltage to control the generator output. The
PCM then sends the proper system voltage messages
to the instrument cluster. If the instrument cluster
turns on the indicator after the bulb test, it may
indicate that the charging system requires service.
For further diagnosis of the charging indicator or the
instrument cluster circuitry that controls the indica-
tor, (Refer to 8 - ELECTRICAL/INSTRUMENT
CLUSTER - DIAGNOSIS AND TESTING). For
proper diagnosis of the charging system, the PCI
data bus, or the electronic message inputs to the
instrument cluster that control the charging indica-
tor, a DRBIIItscan tool is required. Refer to the
appropriate diagnostic information.
COOLANT LOW INDICATOR
DESCRIPTION
A coolant low indicator is only found in the instru-
ment clusters of vehicles equipped with an optional
diesel engine. The coolant low indicator is located
KJINSTRUMENT CLUSTER 8J - 15
BRAKE/PARK BRAKE INDICATOR (Continued)