1995 JEEP YJ ABS

(4) For access to radiator draincock, remove radia-
tor grille mounting screws and remove grill. Refer to
Group 23, Body for procedures.
(5) Attach one end of a 24 inch long X 1/4 inch ID
hose to the radiator draincock. Put the other end into
a clean container. Open draincock and drain radiator.
(6) If equipped, disconnect auxiliary electric cooling
fan electrical connector (Fig. 31).
(7) If equipped, remove two electric cooling fan
mounting bolts. Lift cooling fan straight up until
alignment tabs at the bottom are clear of slots in
bracket at bottom of radiator (Fig. 32).
(8) Remove the two mechanical (non-electrical) fan
shroud mounting bolts. Lift shroud straight up until
alignment tabs at the bottom are clear of slots in
bracket at bottom of radiator (Fig. 32). Place shroud
over mechanical fan.
(9) If equipped, disconnect and plug automatic
transmission fluid cooler lines. Refer to Group 21,
Transmissions for procedures. If equipped with re-
mote transmission cooler, remove line to cooler from
bracket at bottom of radiator.
(10) Disconnect radiator upper and lower hoses
clamps (Figs. 27 and 28). Disconnect radiator upper
and lower hoses.
(11) Mark the position of the hood latch striker on
the radiator crossmember and remove hood latch
striker.(12) Remove two radiator upper crossmember-to-
isolator nuts (Fig. 32).
Fig. 31 Auxiliary Electric Cooling Fan Wiring
ConnectorÐTypical
Fig. 32 Auxiliary Electric Cooling Fan and Fan ShroudÐTypical
JCOOLING SYSTEM SERVICE PROCEDURES 7 - 29

(13) Remove four radiator upper crossmember
bolts (Fig. 32) and remove upper crossmember.
(14) If equipped with air conditioning, separate ra-
diator from condenser by removing condenser-to-radi-
ator mounting brackets (Fig. 33).
(15) Lift radiator straight up and out of engine
compartment taking care not to damage fins.
INSTALLATION
The radiator is supplied with two alignment dowels
(Figs. 32 or 34). They are located on the bottom tank
and fit into rubber grommets in the radiator lower
crossmember.
(1) Lower radiator into engine compartment. Posi-
tion alignment dowels into rubber grommets in radi-
ator lower crossmember (Figs. 32 or 34).
(2) If equipped with air conditioning, attach con-
denser to radiator with mounting brackets (Fig. 33).
(3) Install radiator upper crossmember and four
mounting bolts.
(4) Install radiator upper crossmember-to-isolator
nuts. Tighten nuts to 10 Nzm (86 in. lbs.) torque. If
isolator-to-radiator nuts had been removed, tighten
them to 5 Nzm (47 in. lbs.) torque.
(5) Install hood latch striker. Note previously
marked position.
(6) Connect radiator upper and lower hoses.
(7) If equipped, connect automatic transmission
fluid cooler lines. Refer to Group 21, Transmissions
for procedures. If equipped with remote cooler, attach
cooler line to bracket at bottom of radiator.
(8) Install electric cooling fan (if equipped). Insert
alignment tabs at bottom of fan shroud into slots inbracket at bottom of radiator. Tighten mounting bolts
to3Nzm (31 in. lbs.) torque.
(9) Connect electric cooling fan electrical connector.
(10) Install mechanical cooling fan shroud. Insert
alignment tabs at bottom of shroud into slots in
bracket at bottom of radiator. Tighten mounting bolts
to3Nzm (31 in. lbs.) torque.
(11) Close radiator draincock.
(12) Install grille.
(13) Connect negative battery cable.
(14) Fill cooling system with correct coolant. Refer
to the Coolant section of this group.
(15) Install pressure cap.
(16) Check and adjust automatic transmission
fluid level (if equipped).
YJ MODELS
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If solution is
clean, drain coolant into a clean container for reuse.
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 (NUMBER
6094) (FIG. 27). SNAP-ON CLAMP TOOL (NUMBER
HPC-20) MAY BE USED FOR LARGER CLAMPS. AL-
Fig. 33 Condenser-to-Radiator Mounting BracketsÐ
XJ with 4.0L 6- Cylinder Engine
Fig. 34 Radiator InstallationÐXJ Models with 4.0L
6-Cylinder Engine
7 - 30 COOLING SYSTEM SERVICE PROCEDURESJ

nostic Procedures manual for diagnostic information
and operation of the DRB scan tool.
To test operation of the fan relay only, refer to Re-
laysÐOperation/Testing. This can be found in Group
14, Fuel Systems.
REMOVAL
The auxiliary cooling fan is attached to the radia-
tor upper crossmember behind the radiator.
(1) Remove the two fan mounting bolts from radi-
ator upper crossmember (Fig. 43).
(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 internalradiator mounted transmission oil cooler, engine cool-
ant 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 Test-
ing Cooling System For Leaks sections in this group.
If the transmission operates properly after repairing
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 and
torque convertor may not require reconditioning. Re-
fer to Group 21 for automatic transmission servicing.
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. 44, 45 or 46). It is mounted to
the front frame crossmember.
Fig. 43 Auxiliary Cooling FanÐRemove/InstallÐ
Typical
Fig. 44 Auxiliary Air-To-Oil CoolerÐYJ Models
7 - 36 COOLING SYSTEM SERVICE PROCEDURESJ

BATTERY
GENERAL INFORMATION
The storage battery is a device used to store elec-
trical energy potential in a chemical form. When an
electrical load is applied to the battery terminals, an
electrochemical reaction occurs within the battery.
This reaction causes the battery to discharge electri-
cal current.
The battery is made up of 6 individual cells that
are connected in series. Each cell contains positively
charged plate groups made of lead oxide, and nega-
tively charged plate groups made of sponge lead.
These dissimilar metal plates are submerged in a
sulfuric acid and water solution called electrolyte.
As the battery discharges, a gradual chemical
change takes place within each cell. The sulfuric acid
in the electrolyte combines with the plate materials,
causing both plates to change to lead sulfate. At the
same time, oxygen from the positive plate material
combines with hydrogen from the sulfuric acid, caus-
ing the electrolyte to become mainly water.
The chemical changes within the battery are
caused by movement of excess or free electrons be-
tween the positive and negative plate groups. Thismovement of electrons produces a flow of electrical
current through the load device attached to the bat-
tery terminals.
As the plate materials become more similar chem-
ically, and the electrolyte becomes less acid, the volt-
age potential of each cell is reduced. However, by
charging the battery with a voltage higher than that
of the battery, the process is reversed.
Charging the battery gradually changes the sul-
fated lead plates back into sponge lead and lead ox-
ide, and the water back into sulfuric acid. This action
restores the difference in electron charges deposited
on the plates, and the voltage potential of the battery
cells.
For a battery to remain useful, it must be able to
produce high-amperage current over an extended pe-
riod. A battery must also be able to accept a charge,
so that its voltage potential may be restored.
In addition to producing and storing electrical en-
ergy, the battery serves as a capacitor or voltage sta-
bilizer for the vehicle electrical system. It absorbs
abnormal or transient voltages caused by switching
of any of the vehicle's electrical components.
The battery is vented to release excess gas that is
created when the battery is being charged or dis-
Fig. 1 Starting System Components (Typical)
Fig. 2 Charging System Components (Typical)
8A - 2 BATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICSJ

IGNITION SYSTEMS
CONTENTS
page page
COMPONENT IDENTIFICATION/SYSTEM
OPERATION........................... 1
COMPONENT REMOVAL/INSTALLATION...... 17
DIAGNOSTICS/SERVICE PROCEDURES....... 6IGNITION SWITCHÐXJ MODELS........... 26
IGNITION SWITCHÐYJ MODELS........... 29
SPECIFICATIONS........................ 32
COMPONENT IDENTIFICATION/SYSTEM OPERATION
INDEX
page page
Automatic Shutdown (ASD) Relay.............. 1
Camshaft Position Sensor.................... 2
Crankshaft Position Sensor................... 3
Distributors............................... 4
Engine Coolant Temperature Sensor............ 5
General Information........................ 1Ignition Coil.............................. 4
Intake Manifold Air Temperature Sensor.......... 5
Manifold Absolute Pressure (MAP) Sensor........ 5
Oxygen (O2S) Sensor....................... 5
Powertrain Control Module (PCM).............. 5
Throttle Position Sensor..................... 5
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
²Distributor (contains rotor and camshaft position
sensor)
²Powertrain control module (PCM)
²Crankshaft position sensor
AUTOMATIC SHUTDOWN (ASD) RELAY
The automatic shutdown (ASD) relay is located in
the power distribution center (PDC) near the battery
(Fig. 1 or 2). As one of its functions, it will supply
battery voltage to the ignition coil.
The ground circuit for the ASD relay is controlled
by the powertrain control module (PCM). This is
done through pin/cavity number 51 of the PCM 60-
way connector. The PCM then regulates ASD relay
operation by switching this ground circuit on-and-off.
Also refer to Ignition Coil for additional informa-
tion.
JIGNITION SYSTEMS 8D - 1

On the 4.0L 6-cylinder engine, the ignition coil is
mounted to a bracket on the side of the engine (to
the front of the distributor) (Fig. 11).
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
ENGINE COOLANT TEMPERATURE SENSOR
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR
For an operational description, diagnosis or remov-
al/ installation procedures, refer to Group 14, Fuel
Systems.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
POWERTRAIN CONTROL MODULE (PCM)
The PCM was formerly referred to as the SBEC or
engine controller. On XJ models, the PCM is located
in the engine compartment next to the air cleaner
(Fig. 12). On YJ models, the PCM is located in the
engine compartment behind the windshield washer
fluid reservoir (Fig. 13).
The ignition system is controlled by the PCM.
Base ignition timing by rotation of distributor
is not adjustable.The PCM opens and closes the ig-
nition coil ground circuit to operate the ignition coil.
This is done to adjust ignition timing, both initial
(base) and advance, for changing engine operating
conditions.The amount of electronic spark advance provided
by the PCM is determined by five input factors: En-
gine coolant temperature, engine rpm, intake mani-
fold air temperature, intake manifold absolute
pressure and throttle position.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
For PCM diagnostics, refer to the appropriate Pow-
ertrain Diagnostic Procedures service manual for op-
eration of the DRB scan tool.
THROTTLE POSITION SENSOR
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
OXYGEN (O2S) SENSOR
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
Fig. 11 Ignition CoilÐTypical
Fig. 12 PCM LocationÐXJ Models
Fig. 13 PCM LocationÐYJ Models
JIGNITION SYSTEMS 8D - 5

DIAGNOSTICS/SERVICE PROCEDURES
INDEX
page page
Automatic Shutdown (ASD) Relay Test.......... 6
Camshaft Position Sensor Test................ 6
Crankshaft Position Sensor Test............... 7
Distributor Cap............................ 7
Distributor Rotor........................... 8
DRB Scan Tool............................ 8
Engine Coolant Temperature Sensor Test........ 9
General Information........................ 6
Ignition Coil.............................. 9
Ignition Secondary Circuit Diagnosis........... 10Ignition Timing............................ 11
Intake Manifold Air Temperature Sensor Test..... 11
Manifold Absolute Pressure (MAP) Sensor Test . . . 11
On-Board Diagnostics...................... 15
Oxygen (O2S) Sensor Tests................. 15
Powertrain Control Module (PCM)............. 11
Spark Plug Secondary Cables................ 14
Spark Plugs............................. 12
Throttle Position Sensor Test................. 15
GENERAL INFORMATION
This section of the group, Diagnostics/Service Pro-
cedures, will discuss basic ignition system diagnostics
and service adjustments.
For system operation and component identification,
refer to the Component Identification/System Opera-
tion section of this group.
For removal or installation of ignition system com-
ponents, refer to the Component Removal/Installa-
tion section of this group.
For other useful information, refer to the On-Board
Diagnostics section.
For operation of the DRB Scan Tool, refer to the
appropriate Powertrain Diagnostic Procedures ser-
vice manual.
AUTOMATIC SHUTDOWN (ASD) RELAY TEST
To perform a complete test of this relay and its cir-
cuitry, refer to the DRB scan tool. Also refer to the
appropriate Powertrain Diagnostics Procedures man-
ual. To test the relay only, refer to RelaysÐOpera-
tion/Testing in the Group 14, Fuel Systems section.
CAMSHAFT POSITION SENSOR TEST
To perform a complete test of this sensor and its
circuitry, refer to the DRB scan tool. Also refer to the
appropriate Powertrain Diagnostics Procedures man-
ual. To test the sensor only, refer to the following:
The camshaft position sensor is located in the dis-
tributor (Fig. 1).
To perform a complete test of this sensor and its
circuitry, refer to the DRB scan tool. Also refer to the
appropriate Powertrain Diagnostics Procedures man-
ual. To test the sensor only, refer to the following:
For this test, an analog (non-digital) voltme-
ter is needed.Do not remove the distributor connec-
tor from the distributor. Using small paper clips,
insert them into the backside of the distributor wire
harness connector to make contact with the termi-nals. Be sure that the connector is not damaged
when inserting the paper clips. Attach voltmeter
leads to these paper clips.
(1) Connect the positive (+) voltmeter lead into the
sensor output wire. This is at done the distributor
wire harness connector. For wire identification, refer
to Group 8W, Wiring Diagrams.
(2) Connect the negative (-) voltmeter lead into the
ground wire. For wire identification, refer to Group
8W, Wiring Diagrams.
(3) Set the voltmeter to the 15 Volt DC scale.
(4) Remove distributor cap from distributor (two
screws). Rotate (crank) the engine until the distribu-
tor rotor is pointed to approximately the 11 o'clock
position. The movable pulse ring should now be
within the sensor pickup.
(5) Turn ignition key to ON position. The voltmeter
should read approximately 5.0 volts.
(6) If voltage is not present, check the voltmeter
leads for a good connection.
(7) If voltage is still not present, check for voltage
at the supply wire. For wire identification, refer to
Group 8W, Wiring Diagrams.
Fig. 1 Camshaft Position SensorÐTypical
8D - 6 IGNITION SYSTEMSJ

(4) Crank the engine for 5 seconds while monitor-
ing the voltage at the coil positive terminal:
²If the voltage remains near zero during the entire
period of cranking, refer to On-Board Diagnostics in
Group 14, Fuel Systems. Check the powertrain con-
trol module (PCM) and auto shutdown relay.
²If voltage is at or near battery voltage and drops
to zero after 1-2 seconds of cranking, check the cam-
shaft position sensor-to-PCM circuit. Refer to On-
Board Diagnostics in Group 14, Fuel Systems.
²If voltage remains at or near battery voltage dur-
ing the entire 5 seconds, turn the key off. Remove
the 60-way connector (Fig. 15) from the PCM. Check
60-way connector for any spread terminals.
(5) Remove test lead from the coil positive termi-
nal. Connect an 18 gauge jumper wire between the
battery positive terminal and the coil positive termi-
nal.
(6) Make the special jumper shown in figure 16.
Using the jumper,momentarilyground pin/cavity
number 19 of the PCM 60-way connector. A spark
should be generated at the coil cable when the
ground is removed.
(7) If spark is generated, replace the powertrain
control module (PCM).
(8) If spark is not seen, use the special jumper to
ground the coil negative terminal directly.
(9) If spark is produced, repair wiring harness for
an open condition.
(10) If spark is not produced, replace the ignition
coil.IGNITION TIMING
Base (initial) ignition timing is NOT adjust-
able on any of the 2.5L 4-cylinder or 4.0L 6-cyl-
inder engines. Do not attempt to adjust ignition
timing by rotating the distributor.
Do not attempt to modify the distributor
housing to get distributor rotation. Distributor
position will have no effect on ignition timing.
All ignition timing functions are controlled by the
powertrain control module (PCM). Refer to On-Board
Diagnostics in the Multi-Port Fuel InjectionÐGen-
eral Diagnosis section of Group 14, Fuel Systems for
more information. Also refer to the appropriate Pow-
ertrain Diagnostics Procedures service manual for op-
eration of the DRB Scan Tool.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR
TEST
For an operational description, diagnosis or remov-
al/ installation procedures, refer to Group 14, Fuel
Systems.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
TEST
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
POWERTRAIN CONTROL MODULE (PCM)
The PCM (formerly referred to as the SBEC or en-
gine controller) is located in the engine compartment
behind the windshield washer fluid tank on YJ mod-
els (Fig. 17). It is located in the engine compartment
next to the air cleaner on XJ models (Fig. 18).
The ignition system is controlled by the PCM.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
Fig. 15 PCM 60-Way Connector
Fig. 16 Special Jumper Ground-to-Coil Negative
Terminal
Fig. 17 PCM LocationÐYJ Models
JIGNITION SYSTEMS 8D - 11