1994 JEEP CHEROKEE ECO mode

DIAGNOSIS
INDEX
page page
DRB Scan Tool........................... 5
On-Board Diagnostics (OBD)................. 4Preliminary Checks........................ 5
ON-BOARD DIAGNOSTICS (OBD)
FOR COOLING SYSTEM COMPONENTS
The powertrain control module (PCM) has been
programmed to monitor the certain following cooling
system components:
²If the engine has remained cool for too long a pe-
riod, such as with a stuck open thermostat, a Diag-
nostic Trouble Code (DTC) number 17 can be
observed at the Check Engine Lamp.
²If an open or shorted condition has developed in
the relay circuit controlling the electric radiator fan,
a Diagnostic Trouble Code (DTC) number 35 can be
observed at the Check Engine Lamp.
If the problem is sensed in a monitored circuit of-
ten enough to indicate an actual problem, a DTC is
stored. The DTC will be stored in the PCM memory
for eventual display to the service technician. If the
problem is repaired or ceases to exist, the PCM can-
cels the DTC after 51 engine starts.
Certain criteria must be met for a DTC to be en-
tered into PCM memory. The criteria may be a spe-
cific range of engine rpm, engine temperature and/or
input voltage to the PCM.
A DTC indicates that the PCM has recognized an
abnormal signal in a circuit or the system. A DTC
may indicate the result of a failure, but never iden-
tify the failed component directly.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal-
function has occurred. Refer to On-Board Diagnostics
(OBD) in Group 14, Fuel Systems for additional in-
formation.
ACCESSING DIAGNOSTIC TROUBLE CODES
A stored Diagnostic Trouble Code (DTC) can be dis-
played by cycling the ignition key On-Off-On-Off-On
within three seconds and observing the Malfunction
Indicator Lamp. This lamp was formerly referred to
as the Check Engine Lamp. The lamp is located on
the instrument panel.
They can also be displayed through the use of the
Diagnostic Readout Box (DRB) scan tool. The DRB
connects to the data link connector in the engine
compartment (Figs. 5 or 6). For operation of the
DRB, refer to the appropriate Powertrain Diagnostic
Procedures service manual.EXAMPLES:
²If the lamp flashes 1 time, pauses and flashes 7
more times, a flashing Diagnostic Trouble Code
(DTC) number 17 is indicated.
²If the lamp flashes 3 times, pauses and flashes 5
more times, a flashing Diagnostic Trouble Code
(DTC) number 35 is indicated.
After any stored DTC information has been ob-
served, the display will end with a flashing DTC
number 55. This will indicate the end of all stored
information.
Fig. 5 Data Link ConnectorÐYJ ModelsÐTypical
Fig. 6 Data Link ConnectorÐXJ ModelsÐTypical
7 - 4 COOLING SYSTEMJ

ERASING TROUBLE CODES
After the problem has been repaired, the DRB scan
tool must be used to erase a DTC. Refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual for operation of the DRB scan tool.
DRB SCAN TOOL
For operation of the DRB scan tool, refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual.
PRELIMINARY CHECKS
ENGINE COOLING SYSTEM OVERHEATING
Establish what driving conditions caused the com-
plaint. Abnormal loads on the cooling system such as
the following may be the cause.
1. PROLONGED IDLE, VERY HIGH AMBI-
ENT TEMPERATURE, SLIGHT TAIL WIND AT
IDLE, SLOW TRAFFIC, TRAFFIC JAMS, HIGH
SPEED, OR STEEP GRADES:
Driving techniques that avoid overheating are:
²Idle with A/C off when temperature gauge is at
end of normal range.
²Increasing engine speed for more air flow is recom-
mended.2. TRAILER TOWING:
Consult Trailer Towing section of owners manual.
Do not exceed limits.
3. AIR CONDITIONING; ADD-ON OR AFTER
MARKET:
A maximum cooling package should have been or-
dered with vehicle if add-on or after market A/C is
installed. If not, maximum cooling system compo-
nents should be installed for model involved per
manufacturer's specifications.
4. RECENT SERVICE OR ACCIDENT RE-
PAIR:
Determine if any recent service has been performed
on vehicle that may effect cooling system. This may
be:
²Engine adjustments (incorrect timing)
²Slipping engine accessory drive belt(s)
²Brakes (possibly dragging)
²Changed parts (incorrect water pump rotating in
wrong direction)
²Reconditioned radiator or cooling system refilling
(possibly under-filled or air trapped in system).
If investigation reveals none of the above as a
cause for engine overheating complaint, refer to fol-
lowing Symptom and Action chart.
JCOOLING SYSTEM 7 - 5

CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
ON-BOARD DIAGNOSTICS
XJ and YJ models are equipped with On-Board Di-
agnostics for certain cooling system components. Re-
fer to On-Board Diagnostics (OBD) in the Diagnosis
section of this group for additional information. If the
powertrain control module (PCM) detects low engine
coolant temperature, it will record a Diagnostic Trou-
ble Code (DTC) in the PCM memory. The DTC num-
ber for low coolant temperature is 17. Do not change
a thermostat for lack of heat as indicated by the in-
strument panel gauge or heater performance unless a
DTC number 17 is present. Refer to the Diagnosis
section of this group for other probable causes. For
other DTC numbers, refer to On-Board Diagnostics
in the General Diagnosis section of group 14, Fuel
Systems.
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
nostic Procedures manual for diagnostic information
and operation of the DRB scan tool.
REMOVAL
WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
(1) Drain the coolant from the radiator until the
level is below the thermostat housing.
WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUM-
BER 6094) (FIG. 14). SNAP-ON CLAMP TOOL (NUM-
BER HPC-20) MAY BE USED FOR LARGER
CLAMPS. ALWAYS WEAR SAFETY GLASSES
WHEN SERVICING CONSTANT TENSION CLAMPS.
CAUTION: A number or letter is stamped into the
tongue of constant tension clamps. If replacement
is necessary, use only an original equipment clamp
with matching number or letter.
(2) Remove radiator upper hose and heater hose at
thermostat housing.
(3) Disconnect wiring connector at engine coolant
temperature sensor.(4) Remove thermostat housing mounting bolts,
thermostat housing, gasket and thermostat (Fig. 15).
Discard old gasket.
(5) Clean the gasket mating surfaces.
INSTALLATION
(1) Install the replacement thermostat so that the
pellet, which is encircled by a coil spring, faces the
engine. All thermostats are marked on the outer
flange to indicate the proper installed position.
(a) Observe the recess groove in the engine cyl-
inder head (Fig. 16).
(b) Position thermostat in groove with arrow and
air bleed hole on outer flange pointing up.
(2) Install replacement gasket and thermostat
housing.
Fig. 14 Hose Clamp ToolÐTypical
Fig. 15 Thermostat Removal/Installation
7 - 14 COOLING SYSTEMJ

through the relay. When coolant temperature is be-
low 88ÉC (190ÉF), the PCM opens the ground path to
the relay. This will prevent the cooling fan from be-
ing energized.
Whenever the air conditioning is used, the PCM
engages the auxiliary cooling fan. It provides a
ground path to the cooling fan relay.
DIAGNOSIS
The powertrain control module (PCM) will enter a
diagnostic trouble code (DTC) number 35 in memory
if it detects a problem in the auxiliary cooling fan re-
lay or circuit. This will be read as a flashing signal
at the instrument panel mounted Malfunction Indica-
tor Lamp (formerly referred to as the Check Engine
Lamp). Refer to On-Board Diagnostics in Group 14,
Fuel Systems for information on accessing a DTC.
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
nostic Procedures manual for diagnostic information
and operation of the DRB scan tool.
REMOVAL
The auxiliary fan is attached to the radiator upper
crossmember behind the radiator.
(1) Remove the fan retaining bolts from radiator
upper crossmember (Fig. 41).
(2) Disconnect the electric fan connector.
(3) Lift fan straight up and out of vehicle.
INSTALLATION
(1) Align lower retaining tabs of fan shroud with
slots in bracket at bottom of radiator. Push fan down
into position.
(2) Tighten the mounting bolts to 4 Nzm (31 in.
lbs.) torque.
(3) Connect auxiliary cooling fan electrical connec-
tor.
TRANSMISSION OIL COOLERS
WATER-TO-OIL COOLER
All models equipped with an automatic transmis-
sion are equipped with a transmission oil cooler
mounted internally within the radiator tank. This in-
ternal cooler is supplied as standard equipment on
all models equipped with an automatic transmission.
Transmission oil is cooled when it passes through
this separate cooler. In case of a leak in the internal
radiator mounted transmission oil cooler, engine
coolant may become mixed with transmission fluid or
transmission fluid may enter engine cooling system.
Both cooling system and transmission should be
drained and inspected if the internal radiator
mounted transmission cooler is leaking.
Also refer to the section on Transmission Air-to-Oil
Coolers. This auxiliary air-to-oil cooler is an option
on most engine packages.
REPLACING WATER-TO-OIL COOLER IN
RADIATOR SIDE TANK
The internal transmission oil cooler located within
the radiator is not serviceable. If it requires service,
the radiator must be replaced.
Once the repaired or replacement radiator has been
installed, fill the cooling system and inspect for
leaks. Refer to the Refilling Cooling System and
Testing Cooling System For Leaks sections in this
group. If the transmission operates properly after re-
pairing the leak, drain the transmission and remove
the transmission oil pan. Inspect for sludge and/or
rust. Inspect for a dirty or plugged inlet filter. If
none of these conditions are found, the transmission
Fig. 40 PDCÐXJ Models
Fig. 41 Auxiliary FanÐRemove/Install
JCOOLING SYSTEM 7 - 29

and torque convertor may not require reconditioning.
Refer to Group 21 for automatic transmission servic-
ing.
AIR-TO-OIL COOLER
An auxiliary air-to-oil transmission oil cooler is
available with most engine packages.
On XJ and YJ models, the cooler is located in front
of the radiator or A/C condenser (if equipped) and be-
hind the grill (Figs. 42 or 43). It is mounted to the
front frame crossmember.The auxiliary oil coolers on all models operate in
conjunction with the internal radiator mounted main
oil cooler. The transmission oil is routed through the
main cooler first, then the auxiliary cooler, before re-
turning to the transmission.
REMOVAL/INSTALLATIONÐXJ MODELS
(1) Remove the grill. Refer to Group 23, Body.
(2) Place a drain pan below the transmission oil
cooler.
(3) Remove the two hose clamps at oil cooler inlet
and outlet tubes (Fig. 42).
(4) Remove the two oil cooler mounting bolts (Fig.
42).
(5) Remove the oil cooler from vehicle.
(6) Reverse the preceding operation for installa-
tion. Tighten the two clamps 2 Nzm (15 in. lbs.)
torque.
REMOVAL/INSTALLATIONÐYJ MODELS
(1) Remove fan shroud and radiator. Refer to
Group 7, Cooling for procedures.
(2) Remove the air conditioning filter/drier mount-
ing bolts.
CAUTION: Before proceeding with the next step, be
sure to wear safety glasses. The A/C system is un-
der pressure even with the system off.
(3) Remove the A/C condenser mounting bolts (Fig.
44).
(4) Carefully tilt the A/C condenser rearward for
access to the auxiliary transmission oil cooler.
(5) Place a drain pan below the oil cooler.
(6) Remove the two hose clamps at oil cooler inlet
and outlet tubes (Fig. 43).
(7) Remove the two oil cooler mounting bolts (Fig.
43).
(8) Remove the oil cooler from vehicle.
(9) Reverse the preceding operation for installation.
Tighten the two clamps 2 Nzm (15 in. lbs.) torque.
Fig. 42 Auxiliary Air-To-Oil CoolerÐYJ Models
Fig. 43 Auxiliary Air-To-Oil CoolerÐXJ Models
Fig. 44 Condenser Mounting BoltsÐYJ Models
7 - 30 COOLING SYSTEMJ

IGNITION SYSTEMS
CONTENTS
page page
COMPONENT IDENTIFICATION/SYSTEM
OPERATION.......................... 1
COMPONENT REMOVAL/INSTALLATION..... 20DIAGNOSTICS/SERVICE PROCEDURES....... 8
IGNITION SWITCH...................... 30
SPECIFICATIONS....................... 33
COMPONENT IDENTIFICATION/SYSTEM OPERATION
INDEX
page page
Automatic Shut Down (ASD) Relay............ 1
Camshaft Position Sensor................... 1
Crankshaft Position Sensor.................. 2
Distributors.............................. 3
Engine Coolant Temperature Sensor........... 4
General Information........................ 1Ignition Coil.............................. 4
Intake Manifold Air Temperature Sensor........ 5
Manifold Absolute Pressure (MAP) Sensor...... 5
Powertrain Control Module (PCM)............. 6
Throttle Position Sensor.................... 6
GENERAL INFORMATION
Throughout this group, references are made to par-
ticular vehicle models by alphabetical designation
(XJ or YJ) or by the particular vehicle nameplate. A
chart showing a breakdown of alphabetical designa-
tions is included in the Introduction group at the be-
ginning of this manual.
This section of the group, Component Identifica-
tion/System Operation, will discuss ignition system
operation and will identify ignition system compo-
nents.
For diagnostic procedures and adjustments, refer to
the Diagnostics/Service Procedures section of this
group.
For removal and installation of ignition system
components, refer to the Component Removal/Instal-
lation section of this group.
For other useful information, refer to On-Board Di-
agnostics in the General Diagnosis sections of Group
14, Fuel System in this manual.
For operation of the DRB Scan Tool, refer to the
appropriate Powertrain Diagnostic Procedures ser-
vice manual.
An Ignition specifications section is included at the
end of this group. A general Maintenance Schedule
(mileage intervals) for ignition related items can be
found in Group 0, Lubrication and Maintenance. This
schedule can also be found in the Owners Manual.
IGNITION SYSTEMS
A multi-port, fuel injected engine is used on all
models. The ignition system is controlled by the Pow-
ertrain Control Module (PCM) on all engines. The
PCM was formerly referred to as the SBEC or engine
controller.
The ignition system consists of:
²Spark Plugs
²Ignition Coil
²Secondary Ignition Cables
²Ignition distributor (contains rotor and camshaft
position sensor)
²Powertrain Control Module (PCM)
²Crankshaft Position Sensor
AUTOMATIC SHUT DOWN (ASD) RELAY
The automatic shut down (ASD) relay is located in
the Power Distribution Center (PDC) near the bat-
tery (Fig. 1 or 2). As one of its functions, it will sup-
ply battery voltage to the ignition coil. The ground
circuit for the ASD relay is controlled by the Power-
train Control Module (PCM). The PCM regulates
ASD relay operation by switching the ground circuit
on-and-off.
CAMSHAFT POSITION SENSOR
The camshaft position sensor is located in the igni-
tion distributor (Figs. 3 or 4) on all engines.
The camshaft position sensor contains a hall effect
device called a sync signal generator to generate a
fuel sync signal. This sync signal generator detects a
JIGNITION SYSTEMS 8D - 1

With the ignition key in the ON position and en-
gine not running, check the sensor output voltage at
the center terminal wire of the connector. Check this
at idle (throttle plate closed) and at wide open throt-
tle (WOT). At idle, sensor output voltage should be
greater than 200 millivolts. At wide open throttle,
sensor output voltage must be less than 4.8 volts.
The output voltage should increase gradually as the
throttle plate is slowly opened from idle to WOT.
OXYGEN SENSOR TESTS
For diagnosis, removal or installation, refer to
Group 14, Fuel Systems in this manual.
ON-BOARD DIAGNOSTICS (OBD)
FOR IGNITION SYSTEM COMPONENTS
The powertrain control module (PCM) has been
programmed to monitor certain ignition system cir-
cuits:
EXAMPLE:
If a reference signal is not being detected during
engine cranking from the crankshaft position sensor,
a Diagnostic Trouble Code (DTC) number 11 can be
observed at the Check Engine Lamp.
If the problem is sensed in a monitored circuit of-
ten enough to indicate an actual problem, a DTC is
stored. The DTC will be stored in the PCM memory
for eventual display to the service technician. If the
problem is repaired or ceases to exist, the PCM can-
cels the DTC after 51 engine starts.
Certain criteria must be met for a DTC to be en-
tered into PCM memory. The criteria may be a spe-
cific range of engine rpm, engine temperature and/or
input voltage to the PCM.
A DTC indicates that the PCM has recognized an
abnormal signal in a circuit or the system. A DTC
may indicate the result of a failure, but never iden-
tify the failed component directly.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal-
function has occurred. Refer to On-Board Diagnostics
(OBD) in Group 14, Fuel Systems for additional in-
formation.
ACCESSING DIAGNOSTIC TROUBLE CODES
A stored Diagnostic Trouble Code (DTC) can be dis-
played by cycling the ignition key On-Off-On-Off-On
within three seconds and observing the Malfunction
Indicator Lamp. This lamp was formerly referred to
as the Check Engine Lamp. The lamp is located on
the instrument panel.
They can also be displayed through the use of the
Diagnostic Readout Box (DRB) scan tool. The DRB
connects to the data link connector in the enginecompartment (Figs. 32 or 33). For operation of the
DRB, refer to the appropriate Powertrain Diagnostic
Procedures service manual.
EXAMPLES:
²If the lamp flashes 1 time, pauses and flashes 1
more time, a flashing Diagnostic Trouble Code (DTC)
number 11 is indicated.
²If the lamp flashes 3 times, pauses and flashes 5
more times, a flashing Diagnostic Trouble Code
(DTC) number 35 is indicated.
After any stored DTC information has been ob-
served, the display will end with a flashing DTC
number 55. This will indicate the end of all stored
information.
ERASING TROUBLE CODES
After the problem has been repaired, the DRB scan
tool must be used to erase a DTC. Refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual for operation of the DRB scan tool.
Fig. 32 Data Link ConnectorÐYJ ModelsÐTypical
Fig. 33 Data Link ConnectorÐXJ ModelsÐTypical
JIGNITION SYSTEMS 8D - 19

COMPONENT REMOVAL/INSTALLATION
INDEX
page page
Automatic Shut Down (ASD) Relay........... 20
Camshaft Position Sensor.................. 20
Crankshaft Position Sensor................. 21
Distributor.............................. 23
Engine Coolant Temperature Sensor.......... 22
General Information....................... 20
Ignition Coil............................. 26Intake Manifold Air Temperature Sensor....... 27
Manifold Absolute Pressure (MAP) Sensor..... 27
Oxygen (O2S) Sensor..................... 28
Powertrain Control Module (PCM)............ 28
Spark Plug Secondary Cables............... 29
Spark Plugs............................ 28
Throttle Position Sensor (TPS).............. 29
GENERAL INFORMATION
This section of the group, Component Removal/In-
stallation, will discuss the removal and installation
of ignition system components.
For basic ignition system diagnostics and service
adjustments, refer to the Diagnostics/Service Proce-
dures section of this group.
For system operation and component identification,
refer to the Component Identification/System Opera-
tion section of this group.
AUTOMATIC SHUT DOWN (ASD) RELAY
The ASD relay is installed in the Power Distribu-
tion Center (PDC) (Fig. 1). Relay location is printed
on the PDC cover.
REMOVAL
(1) Remove the PDC cover.
(2) Remove the relay by lifting straight up.
INSTALLATION
(1) Check the condition of relay wire terminals at
PDC before installing relay. Repair as necessary.
(2) Push the relay into the connector.
(3) Install the relay cover.
CAMSHAFT POSITION SENSOR
The camshaft position sensor is located in the dis-
tributor.
REMOVAL
(1) Remove the distributor. Refer to Distributor
Removal.
(2) Remove the distributor rotor.
CAUTION: Do not position the distributor in a vise
when removing or installing the drive gear roll pin.
Support the distributor with wooden blocks.
(3) Mark the position of the gear and the shaft in
line with the roll pin. The gearMUSTbe installed
back to its original position on the distributor shaft.
(4) Using a small pin punch and hammer, remove
the distributor gear roll (spring) pin (Fig. 3).
(5) Lightly tap the end of the distributor shaft un-
til distributor gear and thrust washer are removed.
(6) Slide the distributor shaft out of the distributor
housing.
(7) Remove the camshaft position sensor mounting
screw and positioning arm (Fig. 4).
(8) Slide the wire harness grommet out of the dis-
tributor housing. Remove the camshaft position sen-
sor.
Fig. 1 PDCÐXJ Models
Fig. 2 PDCÐYJ Models
8D - 20 IGNITION SYSTEMSJ