1994 JEEP CHEROKEE wheel

energized). This is done to compensate for the re-
duced flow through injector caused by the lowered
voltage.
BRAKE SWITCHÐPCM INPUT
When the brake light switch is activated, the pow-
ertrain control module (PCM) receives an input indi-
cating that the brakes are being applied. After
receiving this input, the PCM maintains idle speed
to a scheduled rpm through control of the idle air
control (IAC) motor. The brake switch input is also
used to operate the speed control system.
CAMSHAFT POSITION SENSORÐPCM INPUT
A sync signal is provided by the camshaft position
sensor located in the ignition distributor (Fig. 5). The
sync signal from this sensor works in conjunction
with the crankshaft position sensor to provide the
powertrain control module (PCM) with inputs. This
is done to establish and maintain correct injector fir-
ing order.
Refer to Camshaft Position Sensor in Group 8D, Ig-
nition System for more information.
DATA LINK CONNECTORÐPCM INPUT
The data link connector (diagnostic scan tool con-
nector) links the DRB scan tool with the powertrain
control module (PCM). The data link connector is lo-
cated in the engine compartment (Figs. 6 or 7). For
operation of the DRB scan tool, refer to the appropri-
ate Powertrain Diagnostic Procedures service man-
ual.
The data link connector uses two different pins on
the PCM. One is for Data Link Transmit and the
other is for Data Link Receive.
INTAKE AIR TEMPERATURE SENSORÐPCM INPUT
The intake manifold air temperature sensor is in-
stalled in the intake manifold with the sensor ele-
ment extending into the air stream (Figs. 8 or 9).
The sensor provides an input voltage to the power-
train control module (PCM) indicating intake mani-
fold air temperature. The input is used along with
inputs from other sensors to determine injector pulse
width. As the temperature of the air-fuel stream in
the manifold varies, the sensor resistance changes.
This results in a different input voltage to the PCM.
CRANKSHAFT POSITION SENSORÐPCM INPUT
This sensor is a Hall Effect device that detects
notches in the flywheel (manual transmission), or
flexplate (automatic transmission).
This sensor is used to indicate to the powertrain
control module (PCM) that a spark and or fuel injec-
tion event is to be required. The output from this
sensor, in conjunction with the camshaft position
sensor signal, is used to differentiate between fuel in-
jection and spark events. It is also used to synchro-
nize the fuel injectors with their respective cylinders.
Fig. 5 Camshaft Position Sensor
Fig. 6 Data Link ConnectorÐYJ ModelsÐTypical
Fig. 7 Data Link ConnectorÐXJ ModelsÐTypical
14 - 20 FUEL SYSTEMJ

SPEED CONTROLÐPCM INPUT
The speed control system provides three separate
inputs to the powertrain control module (PCM); On/
Off, Set and Resume. The On/Off input informs the
PCM that the speed control system has been acti-
vated. The Set input informs the PCM that a fixed
vehicle speed has been selected. The Resume input
indicates to the PCM that the previous fixed speed is
requested.
The speed control operating range is from 50 km/h
to 142 km/h (35 to 85 mph). Inputs that effect speed
control operation are:
²Park/neutral switch
²Vehicle speed sensor
²Throttle position sensor
Refer to Group 8H for further speed control infor-
mation.
SENSOR RETURNÐPCM INPUT
Sensor Return provides a low noise ground refer-
ence for all system sensors.
THROTTLE POSITION SENSOR (TPS)ÐPCM INPUT
The Throttle Position Sensor (TPS) is mounted on
the throttle body (Figs. 14 or 15). The TPS is a vari-
able resistor that provides the powertrain control
module (PCM) with an input signal (voltage) that
represents throttle blade position. The sensor is con-
nected to the throttle blade shaft. As the position of
the throttle blade changes, the resistance of the TPS
changes.
The PCM supplies approximately 5 volts to the
TPS. The TPS output voltage (input signal to the
PCM) represents the throttle blade position. The
PCM receives an input signal voltage from the TPS.
This will vary in an approximate range of from 1
volt at minimum throttle opening (idle), to 4 volts at
wide open throttle. Along with inputs from other sen-
sors, the PCM uses the TPS input to determine cur-rent engine operating conditions. In response to
engine operating conditions, the PCM will adjust fuel
injector pulse width and ignition timing.
VEHICLE SPEED SENSORÐPCM INPUT
The vehicle speed sensor (Fig. 16) is located in the
extension housing of the transmission (2 wheel drive)
or on the transfer case extension housing (4 wheel
drive). The sensor input is used by the powertrain
control module (PCM) to determine vehicle speed and
distance traveled.
The speed sensor generates 8 pulses per sensor rev-
olution. These signals, in conjunction with a closed
throttle signal from the throttle position sensor, indi-
cate a closed throttle deceleration to the PCM. When
the vehicle is stopped at idle, a closed throttle signal
is received by the PCM (but a speed sensor signal is
not received).
Under deceleration conditions, the PCM adjusts the
idle air control (IAC) motor to maintain a desired
MAP value. Under idle conditions, the PCM adjusts
the IAC motor to maintain a desired engine speed.
Fig. 13 Power Steering Pump Pressure SwitchÐXJ
Models
Fig. 14 Throttle Position SensorÐ2.5L Engine
Fig. 15 Throttle Position SensorÐ4.0L Engine
JFUEL SYSTEM 14 - 23

(29) Verify that fuel pump module wire connector
is firmly connected to harness connector.
(30) Inspect fuel hoses at fuel pump module for
cracks or leaks (Fig. 28).
(31) Inspect transmission torque convertor housing
(automatic transmission) or clutch housing (manual
transmission) for damage to timing ring on drive
plate/flywheel.
(32) Verify that battery cable and solenoid feed
wire connections to the starter solenoid are tight and
clean. Inspect for chaffed wires or wires rubbing up
against other components (Fig. 29).
POWERTRAIN CONTROL MODULE (PCM) 60-WAY
CONNECTOR
For PCM 60-way connector wiring schematics, re-
fer to Group 8W, Wiring Diagrams.
SYSTEM SCHEMATICS
Fuel system schematics for the 2.5L 4 cylinder and
4.0L 6 cylinder engines are shown in figures 30, 31,
32 and 33.
Fig. 28 Fuel Pump Module Connector and Fuel HosesÐTypical
Fig. 29 Starter Solenoid ConnectionsÐTypical
14 - 38 FUEL SYSTEMJ

IDLE AIR CONTROL MOTOR TEST
Idle Air Control (IAC) Motor operation can be
tested using special exerciser tool number 7558 (Fig.
42).
CAUTION: Proper safety precautions must be taken
when testing the idle air control motor:
²Set the parking brake and block the drive wheels
²Route all tester cables away from the cooling fans,
drive belt, pulleys and exhaust components
²Provide proper ventilation while operating the en-
gine
²Always return the engine idle speed to normal be-
fore disconnecting the exerciser tool
(1) With the ignition OFF, disconnect the IAC mo-
tor wire connector at throttle body (Fig. 42).
(2) Plug the exerciser tool number 7558 harness
connector into the IAC motor.
(3) Connect the red clip of exerciser tool 7558 to
battery positive terminal. Connect the black clip tonegative battery terminal. The red light on the exer-
ciser tool will flash when the tool is properly con-
nected.
(4) Start engine.
When the switch on the tool is in the HIGH or
LOW position, the light on the tool will flash. This
indicates that voltage pulses are being sent to the
IAC stepper motor.
(5) Move the switch to the HIGH position. The en-
gine speed should increase. Move the switch to the
LOW position. The engine speed should decrease.
(a) If the engine speed changes while using the
exerciser tool, the IAC motor is functioning prop-
erly. Disconnect the exerciser tool and connect the
IAC motor wire connector to the stepper motor.
(b) If the engine speed does not change, turn the
ignition OFF and proceed to step (6). Do not discon-
nect exerciser tool from the IAC motor.
(6) Remove the IAC motor from the throttle body.
Do not remove IAC motor housing from throttle
body.
CAUTION: When checking IAC motor operation with
the motor removed from the throttle body, do not
extend the pintle (Fig. 43) more than 6.35 mm (.250
in). If the pintle is extended more than this amount,
it may separate from the IAC motor. The IAC motor
must be replaced if the pintle separates from the
motor.
(7) With the ignition OFF, cycle the exerciser tool
switch between the HIGH and LOW positions. Ob-
serve the pintle. The pintle should move in-and-out
of the motor.
(a) If the pintle does not move, replace the idle
air control motor. Start the engine and test the re-
placement motor operation as described in step (5).
(b) If the pintle operates properly, check the idle
air control motor bore in the throttle body bore for
blockage and clean as necessary. Reinstall the idle
air control motor and retest. If blockage is not
Fig. 41 Oxygen SensorÐTypical
Fig. 42 IAC Motor TestingÐTypical
Fig. 43 Idle Air Control (IAC) Motor Pintle
14 - 46 FUEL SYSTEMJ

BRAKES
CONTENTS
page page
ABS BRAKE DIAGNOSIS.................. 3
ABS COMPONENT SERVICE.............. 47
ABS SYSTEM OPERATION............... 39
ANTILOCK BRAKE SYSTEM OPERATION.... 43
BRAKE BLEEDINGÐBRAKE FLUID AND
LEVELÐBRAKELINES AND HOSES....... 13
BRAKE PEDAL AND BRAKELIGHT SWITCH . . 65
DISC BRAKES.......................... 24DRUM BRAKES........................ 34
GENERAL INFORMATION.................. 1
PARKING BRAKES...................... 56
POWER BRAKE BOOSTER................ 22
SERVICE BRAKE DIAGNOSIS.............. 7
SPECIFICATIONS....................... 67
STANDARD MASTER CYLINDER........... 20
GENERAL INFORMATION
INDEX
page page
Antilock Brake System (ABS)................ 1
Brake Fluid/Lubricants/Cleaning Solvents........ 1
Brake Safety Precautions................... 2
Brake Warning Lights...................... 1
Brakelining Material........................ 1Hydraulic Components..................... 1
Jeep Body Code Letters.................... 2
Power Brakes............................ 1
Wheel Brake Components................... 1
WHEEL BRAKE COMPONENTS
Front disc and rear drum brakes are used on all
models. The disc brake components consist of single
piston calipers and ventilated rotors. The rear drum
brakes are dual shoe, units with cast brake drums.
The parking brake mechanism is lever and cable
operated. The cables are attached to actuating levers
mounted on the rear drum brake secondary shoes.
The parking brake mechanism is operated by a foot
pedal on YJ models and a hand lever on XJ models.
POWER BRAKES
Power brakes are standard on all models. A vac-
uum operated power booster is used for standard and
ABS brake applications.
HYDRAULIC COMPONENTS
A dual reservoir master cylinder is used for all
standard brake applications. A combination propor-
tioning valve/pressure differential switch is used. A
center feed style master cylinder is used for ABS
brake applications.
BRAKELINING MATERIAL
The factory installed brakelining on all models con-
sists of an organic base material combined with me-
tallic particles. The lining does not contain asbestos.
BRAKE WARNING LIGHTS
A red, brake warning light is used to alert the
driver if a pressure differential exists between the
front and rear hydraulic systems. The light also
alerts the driver when the parking brakes are ap-
plied. The light illuminates for a few seconds at start
up as part of a bulb check procedure.
An additional warning light is used on models with
antilock brakes. This light is amber in color and is
located in the same side of the instrument cluster as
the red warning light. The amber light illuminates
only when an ABS system fault occurs.
ANTILOCK BRAKE SYSTEM (ABS)
An antilock brake system (ABS) is available on
XJ/YJ models. The system is an electronically oper-
ated, all-wheel brake control system. The ABS sys-
tem is designed to retard wheel lockup during
periods of high wheel slip braking. Refer to the anti-
lock brake section for operation and service informa-
tion.
BRAKE FLUID/LUBRICANTS/CLEANING SOLVENTS
Recommended fluid for all Jeep vehicles is Mopar
DOT 3 brake fluid, or an equivalent meeting SAE
J1703 and DOT 3 standards.
JBRAKES 5 - 1

Use Mopar Multi Mileage grease to lubricate drum
brake pivot pins and rear brakeshoe contact points
on the support plates. Use GE 661, or Dow 111 sili-
cone grease on caliper bushings and mounting bolts.
Use fresh brake fluid or Mopar brake cleaner to
clean or flush brake system components. These are
the only cleaning materials recommended.
CAUTION: Never use gasoline, kerosene, methyl or
isopropyl alcohol, paint thinner, or any fluid con-
taining mineral oil to clean the system components.
These fluids damage rubber cups and seals. If sys-
tem contamination is suspected, check the fluid for
dirt, discoloration, or separation into distinct layers.
Drain and flush the system with new brake fluid if
contamination is suspected.
JEEP BODY CODE LETTERS
The body/model identification code letters for Jeep
vehicles are as follows:
²Code letters XJ: Cherokee
²Code letters YJ: Wrangler/YJ
The code letters are used throughout this group to
simplify model identification and component applica-
tion.
BRAKE SAFETY PRECAUTIONS
WARNING: ALTHOUGH FACTORY INSTALLED
BRAKELINING ON JEEP VEHICLES IS MADE FROM
ASBESTOS FREE MATERIALS, SOME AFTER MARKET
BRAKELINING MAY CONTAIN ASBESTOS. THIS
SHOULD BE TAKEN INTO ACCOUNT WHEN REPAIR-
ING A VEHICLE WITH PRIOR BRAKE SERVICE. WEAR
A RESPIRATOR WHEN CLEANING BRAKE COMPO-
NENTS AS ASBESTOS FIBERS CAN BE A HEALTH
HAZARD. NEVER CLEAN WHEEL BRAKE COMPO-
NENTS WITH COMPRESSED AIR. USE A VACUUM
CLEANER SPECIFICALLY DESIGNED FOR REMOVING
BRAKE DUST. IF A VACUUM CLEANER IS NOT AVAIL-
ABLE, CLEAN THE PARTS WITH WATER DAMPENED
SHOP RAGS. DO NOT CREATE DUST BY SANDING
BRAKELINING. DISPOSE OF ALL DUST AND DIRT
SUSPECTED OF CONTAINING ASBESTOS FIBERS IN
SEALED BAGS OR CONTAINERS. FOLLOW ALL REC-
OMMENDED SAFETY PRACTICES PRESCRIBED BY
THE OCCUPATIONAL SAFETY AND HEALTH ADMINIS-
TRATION (OSHA) AND THE ENVIRONMENTAL PRO-
TECTION AGENCY (EPA), FOR HANDLING AND
DISPOSAL OF PRODUCTS CONTAINING ASBESTOS.
5 - 2 BRAKESJ

ABS BRAKE DIAGNOSIS
INDEX
page page
ABS Fault Diagnosis....................... 4
ABS System Wiring and Electrical Circuits...... 4
ABS Warning Light Display.................. 3
Brake Warning Light Display................. 4
Diagnosis Procedures...................... 3
ECU Diagnosis........................... 4
HCU Diagnosis........................... 4Loss of Sensor Input....................... 3
Operating Sound Levels.................... 3
Rear Speed Sensor Air Gap................. 3
Steering Response........................ 3
Vehicle Response in Antilock Mode............ 3
Wheel/Tire Size and Input Signals............. 3
DIAGNOSIS PROCEDURES
ABS diagnosis involves three basic steps. First is
observation of the warning light display. Second is a
visual examination for low fluid level, leaks, parking
brakes applied, or obvious damage to system compo-
nents or wires. The third step involves using the
DRB II scan tool to identify a faulty component.
The visual examination requires a check of reser-
voir fluid level and all system components. Things to
look for are leaks, loose connections, or obvious com-
ponent damage.
The final diagnosis step involves using the DRB II
scan tool to determine the specific circuit or compo-
nent at fault. The tester is connected to the ABS di-
agnostic connector in the passenger compartment.
The connector is at the driver side of the center con-
sole under the instrument panel. Refer to the DRB II
scan tool Manual for tester procedures. Also refer to
the ABS Fault Diagnosis charts at the end of this
section for additional diagnosis information.
Initial faults should be cleared and the vehicle road
tested to reset any faults that remain in the system.
Faults can be cleared with the DRB II scan tool.
REAR SPEED SENSOR AIR GAP
The front wheel sensors are fixed and cannot be ad-
justed. Only the rear sensor air gap is adjustable. Air
gap must be set with a brass feeler gauge.
Correct air gap is important to proper signal gen-
eration. An air gap that is too large may cause com-
plete loss of sensor input. Or, a gap that is too small
could produce a false input signal, or damaging con-
tact between the sensor and tone ring.
WHEEL/TIRE SIZE AND INPUT SIGNALS
Antilock system operation is dependant on accurate
signals from the wheel speed sensors. Ideally, the ve-
hicle wheels and tires should all be the same size
and type. However, the Jeep ABS system is designed
to function with a compact spare tire installed.
OPERATING SOUND LEVELS
The ABS pump and solenoid valves may produce
some sound as they cycle on and off. This is a normal
condition and should not be mistaken for faulty oper-
ation.
VEHICLE RESPONSE IN ANTILOCK MODE
During antilock braking, the HCU solenoid valves
cycle rapidly in response to ECU inputs.
The driver will experience a pulsing sensation
within the vehicle as the solenoids decrease, hold, or
increase pressure as needed. A pulsing brake pedal
will also be noted.
The pulsing sensation occurs as the solenoids cycle
during antilock mode braking. A slight pulse in the
brake pedal may also be noted during the dynamic
self check part of system initialization.
STEERING RESPONSE
A modest amount of steering input is required dur-
ing extremely high deceleration braking, or when
braking on differing traction surfaces. An example of
differing traction surfaces would be when the left
side wheels are on ice and the right side wheels are
on dry pavement.
LOSS OF SENSOR INPUT
Sensor malfunctions will most likely be due to
loose connections, damaged sensor wires, incorrect
rear sensor air gap, or a malfunctioning sensor. Ad-
ditional causes of sensor faults would be sensor and
tone ring misalignment or damage.
ABS WARNING LIGHT DISPLAY
ABS Light Illuminates At Startup
The amber ABS light illuminates at startup as
part of the system self check feature. The light illu-
minates for 2-3 seconds then goes off as part of the
normal self check routine.
ABS Light Remains On After Startup
An ABS system fault is indicated when the light
remains on after startup. Diagnosis with the DRB II
JBRAKES 5 - 3

scan tool will be necessary to determine which ABS
component has malfunctioned.
ABS Light Illuminates During Brake Stop
A system fault such as loss of speed sensor signal
or solenoid failure, will cause the amber warning
light to illuminate. The most effective procedure here
is to check for obvious damage first. Then check the
electronic components with the DRB II scan tool.
BRAKE WARNING LIGHT DISPLAY
The red brake warning light and the ABS light op-
erate independently. If the red light remains on after
startup or illuminates during a brake stop, refer to
the standard brake system diagnosis section. Either
the parking brakes are applied, or a wheel brake
malfunction has occurred.
ECU DIAGNOSIS
The ECU controls all phases of antilock system op-
eration. It also differentiates between normal and an-
tilock mode braking.
The ECU monitors and processes the signals gen-
erated from all of the system sensors at all times.
The ECU program includes a self check routine
that tests each of the system components. The self
check occurs during both phases of the initialization
program. A failure of the self check program will
cause the immediate illumination of the amber warn-
ing light. The light will also illuminate if a solenoid
or other system component fails during the dynamic
phase of initialization.
If a system malfunction should occur, do not imme-
diately replace the ECU. A blown system fuse, bad
chassis ground, or loss of feed voltage will each cause
a system malfunction similar to an ECU failure.
Never replace the ECU unless diagnosis with the
DRB II scan tool indicates this is necessary.
HCU DIAGNOSIS
The HCU pump and motor and solenoid valve body
are serviced only as an assembly. The HCU assembly
should not be replaced unless a fault has actually
been confirmed. Verify fault conditions with the DRB
II scan tool before proceeding with repair.
ABS SYSTEM WIRING AND ELECTRICAL CIRCUITS
Location of the ABS fuse (in the fuse panel) is
shown in Figure 1. The engine compartment harness
routing for the ABS components is shown in Figure 2.
ABS FAULT DIAGNOSIS
The fault diagnosis chart provides additional infor-
mation on potential ABS system faults. Use the
chart as a guide when diagnosing a system problem.
Fig. 1 ABS Fuse Location
5 - 4 BRAKESJ