heating JEEP CHEROKEE 1994 Service Repair Manual

dye to aid in detecting the source of ATF leaks. The
use of transmission sealing additives should also be
avoided.
Black-light detection dye is factory-installed in
automatic transmissions and, unless the ATF
has been drained and re-placed, it is not neces-
sary to add dye.
ATF LEVEL
Determine the ATF level according to the following
procedure.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT PUT YOUR
HANDS NEAR THE DRIVE BELT, PULLEYS OR FAN
BLADE. DO NOT STAND IN A DIRECT LINE WITH
THE FAN BLADE.
(1) Operate the engine and allow the automatic
transmission sufficient time to warm to the normal
operating temperature (77ÉC/170ÉF).
When at normal operating temperature, ATF
will be uncomfortable to fingertips when the
dipstick is touched. Normally, 25 km (15 miles) is
a sufficient driving distance for a transmission
to warm to normal operating temperature (77ÉC/
170ÉF).
(2) Place the vehicle on a level surface.
(3) Operate the engine at idle speed.
(4) Engage the parking brake.
(5) Place a block in front of and at the rear of one
wheel/tire to prevent vehicle movement.
(6) Depress the brake pedal and move the trans-
mission selector lever through all the positions and
then place the selector lever in NEUTRAL position.
(7) Remove the dipstick (Fig. 6) from the transmis-
sion filler tube and wipe it clean.
(8) Insert the dipstick into the transmission filler
tube and seat the cap on top of the tube.
(9) Remove the dipstick and observe the ATF level
on both sides of the dipstick. The ATF level is accept-
able when it is between the ADD and FULL marks.
(10) While determining the ATF level in a trans-
mission, also note the general condition of the fluid.
Examine the fluid closely. If doubtful about its con-
dition, drain a sample into a small container for
evaluation.
(11) If the ATF level is either at or below the ADD
mark, add sufficient ATF to raise the level to the
FULL mark on the dipstick.
CAUTION: Do not over-fill an automatic transmis-
sion. Over-filling can cause the ATF to foam, which
will result in over-heating, fluid oxidation and var-
nish formation.
(12) When it is necessary to add ATF, insert a
long-necked funnel into the transmission filler tube.It requires only 0.5 liter (1.0 pint) of ATF to raise
the level from the ADD mark to the FULL mark.
(13) Inspect for ATF leaks and correct as neces-
sary.
(14) Remove the wheel/tire blocks.
ATF AND FILTER CHANGE
Automatic transmission fluid (ATF) does not dete-
riorate or wear out, but it does become contaminated.
These contaminates will eventually restrict passages
and orifices. The result is hard or rough shifting, or
complete transmission failure. Also, the varnish
eventually causes rubber seals to harden and become
brittle.
When it is necessary to change the ATF and re-
place the filter in a Jeeptautomatic transmission,
use the following procedures.
Fig. 6 Dipstick & ATF LevelÐTypical
Fig. 7 Safe ATF Level Above 22ÉC/72ÉF
0 - 24 LUBRICATION AND MAINTENANCEJ

(6) Inspect the disc brake caliper dust boot for cor-
rect installation, damage/tears and indications of
brake fluid leakage. Inspect the bushings and pins
for corrosion, tears and a binding condition.
(7) Pull the rear wheel cylinder dust boot back to
expose the wheel cylinder housing and inspect for
fluid leaks. Inspect the pistons and cylinder bores for
proper appearance.
(8) Inspect the brake differential warning valve
and housing for indications of leakage, kinked hoses
and loose fittings.
PARK BRAKE
(1) As applicable, engage the park brake lever or
pedal and then release it.
(2) If the park brake is functioning normally, test
it for smooth operation and vehicle-holding capabil-
ity.
(3) Inspect the park brake cables for kinks, fraying
and a binding condition.
(4) With the park brake released, the rear wheels
should rotate without restriction. Adjust the park
brake cable tension at the equalizer (Fig. 10), if nec-
essary.
(5) Repair any park brake malfunctions.
BRAKE OPERATIONAL TEST
(1) Drive the vehicle and test for proper brake ac-
tion.
(2) Note any indication of drum/rotor overheating,
wheel dragging or the vehicle pulling to one side
when the brakes are applied.
(3) Evaluate any performance complaints received
from the owner/operator.
(4) Repair the brake system as necessary (refer to
Group 5ÐBrakes for additional information and ser-
vice procedures).
TIRES
RECOMMENDED MAINTENANCE
The general condition of the tires and the inflation
pressures should be inspected at the same time the
engine oil is changed and the oil filter is replaced.
In addition, the tires/wheels should be rotated pe-
riodically to ensure even tread wear and maximum
tread life. The tires/wheels should be rotated initially
after the first 12 000-km (7,500-miles). Thereafter,
after each 24 000-km (15,000-miles) interval of vehi-
cle operation has elapsed.
INSPECTION
Inspect the tires for excessive wear, damage, etc.
Test the tires for the recommended inflation pres-
sure. Refer to the tire inflation pressure decal located
on the inside of the glove box door, and also to Group
22ÐTires And Wheels.
ROTATION
Refer to Group 22ÐTires And Wheels for the rec-
ommended method of tire/wheel rotation for a Jeept
vehicle.
BODY COMPONENTS
RECOMMENDED MAINTENANCE
Body components should be lubricated (as required)
after each 48 000-km (30,000-miles) interval of vehi-
cle operation has elapsed.
LUBRICANT SPECIFICATIONS
All applicable exterior and interior body compo-
nents should be:
²inspected for excessive wear,
²cleaned, and
²all pivot/sliding contact areas of the components
should be lubricated with the specified lubricant.
Refer to the Body Lubricant Specifications chart
below. When excessive wear is apparent, replace/re-
pair as necessary.
LUBRICATION
All pivoting and sliding contact areas, including:
²seat tracks,
²door hinges/latches/strikers, and
²liftgate/tailgate/hood hinges (Fig. 11),
should be lubricated periodically to ensure quiet,
easy operation and to protect against wear and cor-
rosion.
(1) As required, lubricate the body components
with the specified lubricants.
(2) When lubricating door weatherstrip seals, ap-
ply the lubricant to a cloth and wipe it on the seal.
(3) Prior to the application of lubricant, the compo-
nent should be wiped clean to remove dust, grit and
debris. After lubrication, any excess lubricant should
be removed.
Fig. 10 Park Brake Equalizer (XJ)ÐTypical
0 - 34 LUBRICATION AND MAINTENANCEJ

not change except when a spindle or ball stud is
damaged or bent. The angle is not adjustable and the
damaged component(s) must be replaced to correct
mis-alignment.
CAUTION:Do not attempt to modify any suspension
or steering component by heating and bending.
PRE-ALIGNMENT INSPECTION
Before starting a front wheel alignment, the follow-
ing inspection and necessary corrections must be
completed.
(1) Tires with the same recommended air pressure,
size, and thread wear. Refer to Group 22, Tires And
Wheels for diagnosis information.
(2) Front wheel bearings for wear.
(3) Ball studs, steering linkage pivot points and
steering gear for looseness, roughness, binding or
wear. Refer to Group 19, Steering for additional in-
formation.
(4) Front wheels for excessive radial or lateral
runout and unbalance. Refer to Group 22, Tires And
Wheels for diagnosis information.
(5) Suspension components for wear and noise.
Check components for correct torque. Refer to Groups
2 and 3, Suspension and Axle for additional informa-
tion.
ALIGNMENT MEASUREMENTS AND ADJUSTMENTS
Before each alignment reading, the vehicle should
be jounced (rear first, then front). Grasp each bumper
at the center and jounce the vehicle up and down
several times. Always release the bumper in the
down position.Set the front end alignment to
specifications with the vehicle at its NOR-
MALLY RIDE HEIGHT.
CAMBER
The wheel camber angle (Fig. 1) is preset at ZERO
DEGREES (0É). The angle is not adjustable and can-
not be altered.
CASTER
The caster angle (Fig. 1) is set at:
²XJ manual transmission, POSITIVE 6.5 DE-
GREES (+6.5É).
²XJ automatic transmission, POSITIVE 8.0 DE-
GREES (+8.0É).
²YJ all transmissions, POSITIVE 6.0 DEGREES
(+6.0É).
Before checking the caster of the front axle for cor-
rect angle. Be sure the axle is not bent or twisted.
Road test the vehicle, and make left and right
turns. If the steering wheel returns to the center po-
sition unassisted, the caster angle is correct. How-ever, if steering wheel does not return toward the
center position unassisted, an incorrect caster angle
is probable.
Caster can be adjusted by installing the appropri-
ate size shims (Fig. 2, 3).Changing caster angle
will also change the front propeller shaft angle.
The propeller shaft angle has priority over
caster. Refer to Group 16, Propeller Shafts for
additional information.
Fig. 2 AdjustmentÐYJ Vehicles
Fig. 3 AdjustmentÐXJ Vehicles
2 - 6 FRONT SUSPENSION AND AXLEJ

AXLE NOISE/VIBRATION DIAGNOSIS
INDEX
page page
Driveline Snap........................... 17
Gear and Bearing Noise................... 16
General Information....................... 16Low Speed Knock........................ 17
Vibration............................... 17
GENERAL INFORMATION
Axle bearing problem conditions are usually caused
by:
²Insufficient or incorrect lubricant
²Foreign matter/water contamination
²Incorrect bearing preload torque adjustment
²Incorrect backlash (to tight)
When serviced, the bearings must be cleaned thor-
oughly. They should be dried with lint-free shop tow-
els.Never dry bearings with compressed air.
This will overheat them and brinell the bearing
surfaces. This will result in noisy operation after
repair.
Axle gear problem conditions are usually the result
of:
²Insufficient lubrication
²Incorrect or contaminated lubricant
²Overloading (excessive engine torque) or exceeding
vehicle weight capacity
²Incorrect clearance or backlash adjustment
Insufficient lubrication is usually the result of a
housing cover leak. It can also be from worn axle
shaft or pinion gear seals. Check for cracks or porous
areas in the housing or tubes.
Using the wrong lubricant will cause overheating
and gear failure. Gear tooth cracking and bearing
spalling are indicators of this.
Axle component breakage is most often the result
of:
²Severe overloading
²Insufficient lubricant
²Incorrect lubricant
²Improperly tightened components
Overloading occurs when towing heavier than rec-
ommended loads. Component breakage can occur
when the wheels are spun excessively. Incorrect lu-
bricant quantity contributes to breakage. Loose dif-
ferential components can also cause breakage.
Incorrect bearing preload or gear backlash will not
result in component breakage. Mis-adjustment will
produce enough noise to cause service repair before a
failure occurs. If a mis-adjustment condition is not
corrected, component failure can result.
Excessive bearing preload may not be noisy. This
condition will cause high temperature which can re-
sult in bearing failure.
GEAR AND BEARING NOISE
GEAR NOISE
Axle gear noise can be caused by insufficient lubri-
cant. Incorrect backlash, tooth contact, or worn/dam-
aged gears can cause noise.
Gear noise usually happens at a specific speed
range. The range is 30 to 40 mph, or above 50 mph.
The noise can also occur during a specific type of
driving condition. These conditions are acceleration,
deceleration, coast, or constant load.
When road testing, accelerate the vehicle to the
speed range where the noise is the greatest. Shift
out-of-gear and coast through the peak-noise range.
If the noise stops or changes greatly, check for insuf-
ficient lubricant. Incorrect ring gear backlash, or
gear damage can cause noise changes.
Differential side and pinion gears can be checked
by turning the vehicle. They usually do not cause
noise in straight-ahead driving. These gears are
loaded during vehicle turns. If noise does occur dur-
ing vehicle turns, the side or pinion gears could be
worn or damaged. A worn pinion gear mate shaft can
also cause a snapping or a knocking noise.
BEARING NOISE
The axle shaft, differential and pinion gear bear-
ings can all produce noise when worn or damaged.
Bearing noise can be either a whining, or a growling
sound.
Pinion gear bearings have a constant-pitch noise.
This noise changes only with vehicle speed. Pinion
bearing noise will be higher because it rotates at a
faster rate. Drive the vehicle and load the differen-
tial. If bearing noise occurs the pinion rear bearing is
the source of the noise. If the bearing noise is heard
during a coast, front bearing is the source.
Worn, damaged differential bearings usually pro-
duce a low pitch noise. Differential bearing noise is
similar to pinion bearing. The pitch of differential
bearing noise is also constant and varies only with
vehicle speed.
Axle shaft bearings produce noise and vibration
when worn or damaged. The noise generally changes
when the bearings are loaded. Road test the vehicle.
Turn the vehicle sharply to the left and to the right.
This will load the bearings and change the noise
2 - 16 FRONT SUSPENSION AND AXLEJ

BACKLASH AND CONTACT PATTERN ANALYSIS
(1) Rotate assembly several revolutions to seat
bearings. Measure backlash at three equally spaced
locations around the perimeter of the ring gear with
a dial indicator (Fig. 63).
The ring gear backlash must be within 0.005 -
0.008 inch (0.12 - 0.20 mm). It cannot vary more
than 0.002 inch (0.05 mm) between the points
checked.
If backlash must be adjusted, transfer shims from
one side of carrier to the other side. Adjust the back-
lash accordingly (Fig. 64).DO NOT INCREASE
THE TOTAL SHIM PACK THICKNESS, EXCES-
SIVE BEARING PRELOAD AND DAMAGE
WILL OCCUR.If the mesh and backlash steps have been followed
in the procedures above, good gear teeth contact pat-
terns should exist.
The ring gear teeth contact patterns will show if
the pinion gear depth is correct. It will also show if
the ring gear backlash has been adjusted correctly.
The backlash must be maintained within the speci-
fied limits until the correct tooth contact patterns are
obtained.
(2) Apply a thin coat of hydrated ferric oxide (yel-
low oxide of iron) to the drive and coast side of the
ring gear teeth.
(3) Rotate the ring gear one complete revolution in
both directions while a load is being applied. Insert a
pry bar between the differential housing and the case
flange. This action will produce distinct contact pat-
terns on both the drive side and coast side of the ring
gear teeth.
(4) Note patterns in compound. Refer to (Fig. 65)
for interpretation of contact patterns and adjust ac-
cordingly.
FINAL ASSEMBLY
(1) Install the axle shafts. Refer to Axle Shaft In-
stallation in this Group.
(2) Scrape the residual sealant from the housing
and cover mating surfaces. Clean the mating sur-
faces with mineral spirits. Apply a bead of MOPARt
Silicone Rubber Sealant on the housing cover (Fig.
66). Allow the sealant to cure for a few minutes.
Install the housing cover within 5 minutes af-
ter applying the sealant. If not installed the seal-
ant must be removed and another bead applied.
(3) Install the cover on the differential with the at-
taching bolts. Install the identification tag. Tighten
the cover bolts with 41 Nzm (30 ft. lbs.) torque.
CAUTION: Overfilling the differential can result in
the lubricant foaming and overheating.
(4) Refill the differential housing with the speci-
fied quantity of MOPARtHypoid Gear Lubricant.
(5) Install the fill hole plug and tighten to 34 Nzm
(25 ft. lbs.) torque.Fig. 63 Ring Gear Backlash Measurement
Fig. 64 Backlash Shim Adjustment
2 - 44 FRONT SUSPENSION AND AXLEJ

OVERDRIVE/OVERRIDE SWITCH
On vehicles equipped with overdrive, the power-
train control module (PCM) regulates the 3-4 over-
drive up-shift and down-shift through the overdrive
solenoid.
Refer to Group 21 for more information.
OXYGEN (O2S) SENSORÐPCM INPUT
The O2S sensor is located in the exhaust down pipe
(Fig. 11). It provides an input voltage to the power-
train control module (PCM) relating the oxygen con-
tent of the exhaust gas. The PCM uses this
information to fine tune the air-fuel ratio by adjust-
ing injector pulse width.
The O2S sensor produces voltages from 0 to 1 volt.
This voltage will depend upon the oxygen content of
the exhaust gas in the exhaust manifold. When a
large amount of oxygen is present (caused by a lean
air-fuel mixture), the sensor produces a low voltage.
When there is a lesser amount present (rich air-fuel
mixture) it produces a higher voltage. By monitoring
the oxygen content and converting it to electrical
voltage, the sensor acts as a rich-lean switch.
The oxygen sensor is equipped with a heating ele-
ment that keeps the sensor at proper operating tem-
perature during all operating modes. Maintaining
correct sensor temperature at all times allows the
system to enter into closed loop operation sooner.
In Closed Loop operation, the powertrain control
module (PCM) monitors the O2S sensor input (along
with other inputs). It then adjusts the injector pulse
width accordingly. During Open Loop operation, the
PCM ignores the O2S sensor input and adjusts injec-
tor pulse width to a preprogrammed value (based on
other sensor inputs).
PARK/NEUTRAL SWITCHÐPCM INPUT
The park/neutral switch is located on the transmis-
sion housing and provides an input to the powertrain
control module (PCM). This will indicate that the au-
tomatic transmission is in Park, Neutral or a drivegear selection. This input is used to determine idle
speed (varying with gear selection), fuel injector
pulse width and ignition timing advance. Refer to
Group 21, Transmissions, for testing, replacement
and adjustment information.
POWER GROUND
The power ground is used to control ground circuits
for the following powertrain control module (PCM)
loads:
²Generator Field Winding
²8 volt (PCM) power supply
²Fuel Injectors
²Ignition Coil
POWER STEERING PRESSURE SWITCHÐPCM
INPUT
A pressure sensing switch is included in the power
steering system (mounted on the high-pressure line).
This switch will be on vehicles equipped with a 2.5L
engine and power steering. The switch (Fig. 12 YJ
Models or Fig. 13 XJ Models) provides an input to
the PCM. This input is provided during periods of
high pump load and low engine rpm; such as during
parking maneuvers. The PCM will then increase the
idle speed through the idle air control (IAC) motor.
This is done to prevent the engine from stalling un-
der the increased load.
When steering pump pressure exceeds 1896 kPa6
172 kPa (275625 psi) the PCM will increase the en-
gine idle speed. This will prevent the engine from
stalling.
SCI RECEIVEÐPCM INPUT
SCI Receive is the serial data communication re-
ceive circuit for the DRB scan tool. The powertrain
control module (PCM) receives data from the DRB
through the SCI Receive circuit.
Fig. 11 Heated Oxygen Sensor LocationÐTypical
Fig. 12 Power Steering Pump Pressure SwitchÐYJ
Models
14 - 22 FUEL SYSTEMJ

AIR CONDITIONING (A/C) CLUTCH RELAYÐPCM
OUTPUT
The powertrain control module (PCM) activates the
A/C compressor through the A/C clutch relay. The
PCM regulates A/C compressor operation by switch-
ing the ground circuit for the A/C clutch relay on
and off. The relay is located in the Power Distribu-
tion Center (PDC) (Figs. 17 or 18). For the location of
the relay within the PDC, refer to label on PDC
cover.
When the PCM receives a request for A/C from A/C
evaporator switch, it will adjust idle air control (IAC)
motor position. This is done to increase idle speed.
The PCM will then activate the A/C clutch through
the A/C clutch relay. The PCM adjusts idle air con-
trol (IAC) stepper motor position to compensate for
increased engine load from the A/C compressor.
By switching the ground path for the relay on and
off, the PCM is able to cycle the A/C compressor
clutch. This is based on changes in engine operating
conditions. If, during A/C operation, the PCM senses
low idle speeds or a wide open throttle condition, itwill de-energize the relay. This prevents A/C clutch
engagement. The relay will remain de-energized un-
til the idle speed increases or the wide open throttle
condition exceeds 15 seconds or no longer exists. The
PCM will also de-energize the relay if coolant tem-
perature exceeds 125ÉC (257ÉF).
AUTO SHUT DOWN (ASD) RELAYÐPCM OUTPUT
The ASD relay is located in the Power Distribution
Center (PDC) (Figs. 17 or 18). For the location of this
relay within the PDC, refer to label on PDC cover.
The ASD supplies battery voltage to the fuel pump,
fuel injector, ignition coil, generator field winding
and oxygen (O2S) sensor heating element. The
ground circuit for the coil in the ASD relay is con-
trolled by the powertrain control module (PCM). The
PCM operates the relay by switching the ground cir-
cuit on and off.
The fuel pump relay is controlled by the PCM
through same circuit that the ASD relay is con-
trolled.
The powertrain control module (PCM) energizes
the fuel pump through the fuel pump relay. (The
PCM was formerly referred to as the SBEC or engine
controller). Battery voltage is applied to the relay
from the ignition switch. The relay is energized when
a ground is provided by the PCM. The relay is lo-
cated in the Power Distribution Center (PDC) (Figs.
17 or 18). For the location of fuel pump relay within
PDC, refer to label on PDC cover.
For the 1994 model year, the ballast resistor and
ballast resistor bypass relay are no longer used to
control the fuel pump circuit.
DATA LINK CONNECTORÐPCM OUTPUT
Refer to the previous paragraphs on Data Link
ConnectorÐPCM Input for information.
EMR LAMPÐPCM OUTPUT
The EMR lamp is not used for the 1994 model
year.
Fig. 16 Vehicle Speed SensorÐTypical
Fig. 17 PDCÐYJ Models
Fig. 18 PDCÐXJ Models
14 - 24 FUEL SYSTEMJ

MULTI-PORT FUEL INJECTION (MFI)ÐGENERAL DIAGNOSIS
INDEX
page page
Automatic Shutdown (ASD) Relay Testing...... 43
Camshaft Position Sensor Test.............. 43
Crankshaft Position Sensor Test............. 44
Diagnostic Trouble Code (DTC).............. 51
DRB Scan Tool.......................... 51
Engine Coolant Temperature Sensor Test...... 43
Extended Idle Switch Test.................. 45
Fuel Pump Relay Testing.................. 44
Fuel System Pressure Test................. 48
General Information....................... 32
Idle Air Control Motor Test................. 46
Injector Test............................ 48
Intake Air Temperature Sensor Test.......... 43Manifold Absolute Pressure (MAP) Sensor Test . 44
On-Board Diagnostics (OBD)................ 48
Oxygen Sensor (O2S) Heating Element Test.... 45
Powertrain Control Module (PCM) 60-Way
Connector............................ 38
RelaysÐOperation/Testing.................. 47
Starter Motor Relay Test................... 48
System Schematics....................... 38
Throttle Position Sensor (TPS) Test.......... 45
Torque Converter Clutch Relay Test.......... 45
Vehicle Speed Sensor Test................. 45
Visual Inspection......................... 32
GENERAL INFORMATION
All 2.5L 4 cylinder and 4.0L 6 cylinder engines are
equipped with sequential Multi-Port Fuel Injection
(MFI). The MFI system provides precise air/fuel ra-
tios for all driving conditions.
VISUAL INSPECTION
A visual inspection for loose, disconnected, or incor-
rectly routed wires and hoses should be made. This
should be done before attempting to diagnose or ser-
vice the fuel injection system. A visual check will
help spot these faults and save unnecessary test and
diagnostic time. A thorough visual inspection will in-
clude the following checks:
(1) Verify that the 60-way connector is fully inserted
into the connector of the Powertrain Control Module
(PCM) (Figs. 1 or 2). Verify that the connector mount-
ing bolt is tightened to 4 Nzm (35 in. lbs.) torque.
(2) Inspect the battery cable connections. Be sure
they are clean and tight.
(3) Inspect fuel pump relay and air conditioning com-
pressor clutch relay (if equipped). Inspect ASD relay andradiator fan relay (if equipped) connections. Inspect starter
motor relay connections. Inspect relays for signs of physical
damage and corrosion. The relays are installed in the
Power Distribution Center (PDC) (Figs. 3 or 4).
Fig. 1 PCMÐYJ Models
Fig. 2 PCMÐXJ Models
Fig. 3 PDCÐYJ Models
14 - 32 FUEL SYSTEMJ

EXTENDED IDLE SWITCH TEST
OPTIONAL POLICE PACKAGE ONLY
OPERATION
The extended idle switch is used to raise the en-
gine idle speed to approximately 1000 rpm when the
shifter is in either the Park or Neutral position. A
rocker-type 2-wire switch (extended idle switch) is
mounted to the instrument panel.This switch is
available only with 4.0L engine when supplied
with the optional police package.
TESTING
The extended idle switch will control a ground cir-
cuit going to the powertrain control module (PCM).
When a ground signal (through this switch) has been
received at pin number 10 in the PCM, engine idle
speed will increase.
Bring the engine to normal operating temperature
and turn the extended idle switch to the ON position.
Engine speed should now increase to approximately
1000 rpm when the shifter is in either the Park or
Neutral position. If engine speed does not increase,
apply a good ground to pin number 10 at the PCM
using a small paper clip. Be careful not to damage
the wiring with the paper clip. If the engine speed
now increases, it can be assumed that the PCM is
functioning correctly. Check the instrument panel
mounted switch for a closed ground circuit when in
the ON position. If the engine speed will not increase
after applying a ground to pin number 10, replace
the PCM. Refer to Group 8W, Wiring Diagrams for
circuit and wiring information.
THROTTLE POSITION SENSOR (TPS) TEST
To perform a complete test of the sensor and its cir-
cuitry, refer to DRB scan tool and appropriate Pow-
ertrain Diagnostics Procedures manual. To test the
sensor only, refer to the following:
The throttle position sensor (TPS) can be tested
with a digital voltmeter. The center terminal of the
TPS is the output terminal (Figs. 39 or 40).
With the ignition key in the ON position, back-
probe the TPS connector. Check the TPS output volt-
age at the center terminal wire of the connector.
Check this at idle (throttle plate closed) and at wide
open throttle (WOT). At idle, TPS output voltage
should must be greater than 200 millivolts. At wide
open throttle, TPS output voltage must be less than
4.8 volts. The output voltage should increase gradu-
ally as the throttle plate is slowly opened from idle to
WOT.
TORQUE CONVERTER CLUTCH RELAY TEST
To test the relay only, refer to RelaysÐOperation/
Testing in this section of the group. To test the
torque converter clutch circuit and related compo-nents, refer to the appropriate Powertrain Diagnostic
Procedures manual for operation of the DRB scan
tool.
VEHICLE SPEED SENSOR TEST
To perform a complete test of the sensor and its cir-
cuitry, refer to DRB scan tool and appropriate Pow-
ertrain Diagnostics Procedures manual.
OXYGEN SENSOR (O2S) HEATING ELEMENT TEST
To perform a complete test of the O2S sensor (Fig.
41) and its circuitry, refer to DRB scan tool and ap-
propriate Powertrain Diagnostics Procedures manual.
To test the sensor only, refer to the following:
The oxygen sensor heating element can be tested
with an ohmmeter as follows:
With the sensor at room temperature 25 degrees C
(77 degrees F), disconnect the O2S sensor connector.
Connect the ohmmeter test leads across the white
wire terminals of the sensor connector. Resistance
should be between 5 and 7 ohms. Replace the sensor
if the ohmmeter displays an infinity (open) reading.
Fig. 39 TPS TestingÐ2.5L Engine
Fig. 40 TPS TestingÐ4.0L Engine
JFUEL SYSTEM 14 - 45

Brake drag also has a direct effect on fuel economy.
If undetected, minor brake drag can be misdiagnosed
as an engine or transmission/torque converter prob-
lem.
Minor drag will usually cause slight surface char-
ring of the lining. It can also generate hard spots in
rotors and drums from the overheat/cool down pro-
cess. In most cases, the rotors, drums, wheels and
tires are quite warm to the touch after the vehicle is
stopped.
Severe drag can char the brake lining all the way
through. It can also distort and score rotors and
drums to the point of replacement. The wheels, tires
and brake components will be extremely hot. In se-
vere cases, the lining may generate smoke as it chars
from overheating.
An additional cause of drag involves the use of in-
correct length caliper mounting bolts. Bolts that are
too long can cause a partial apply condition. The cor-
rect caliper bolts have a shank length of 67 mm
(2.637 in.), plus or minus 0.6 mm (0.0236 in.). Refer
to the Disc Brake service section for more detail on
caliper bolt dimensions and identification.
Some common causes of brake drag are:
²loose or damaged wheel bearing
²seized or sticking caliper or wheel cylinder piston
²caliper binding on bushings or slide surfaces
²wrong length caliper mounting bolts (too long)
²loose caliper mounting bracket
²distorted brake drum or shoes
²rear brakeshoes binding on worn/damaged support
plates
²severely rusted/corroded components
²misassembled components.
If brake drag occurs at all wheels, the problem may
be related to a blocked master cylinder compensator
port or faulty power booster (binds-does not release).
The brakelight switch can also be a cause of drag.
An improperly mounted or adjusted brakelight
switch can prevent full brake pedal return. The re-
sult will be the same as if the master cylinder com-
pensator ports are blocked. The brakes would be
partially applied causing drag.
BRAKE FADE
Brake fade is a product of overheating caused by
brake drag. However, overheating and subsequent
fade can also be caused by riding the brake pedal,
making repeated high deceleration stops in a short
time span, or constant braking on steep roads. Refer
to the Brake Drag information in this section for
causes.
PEDAL PULSATION
Pedal pulsation is caused by components that are
loose, or beyond tolerance limits.
Disc brake rotors with excessive lateral runout or
thickness variation, or out of round brake drums arethe primary causes of pulsation. Other causes are
loose wheel bearings or calipers and worn, damaged
tires.
PULL
A front pull condition could be the result of:
²contaminated lining in one caliper
²seized caliper piston
²binding caliper
²wrong caliper mounting bolts (too long)
²loose caliper
²loose or corroded mounting bolts
²improper brakeshoes
²damaged rotor
²incorrect wheel bearing adjustment (at one wheel)
A worn, damaged wheel bearing or suspension
component are further causes of pull. A damaged
front tire (bruised, ply separation) can also cause
pull. Wrong caliper bolts (too long) will cause a par-
tial apply condition and pull if only one caliper is in-
volved.
A common and frequently misdiagnosed pull condi-
tion is where direction of pull changes after a few
stops. The cause is a combination of brake drag fol-
lowed by fade at the dragging brake unit.
As the dragging brake overheats, efficiency is so
reduced that fade occurs. If the opposite brake unit is
still functioning normally, its braking effect is mag-
nified. This causes pull to switch direction in favor of
the brake unit that is functioning normally.
When diagnosing a change in pull condition, re-
member that pull will return to the original direction
if the dragging brake unit is allowed to cool down
(and is not seriously damaged).
REAR BRAKE GRAB
Rear grab (or pull) is usually caused by contami-
nated lining, bent or binding shoes and support
plates, or improperly assembled components. This is
particularly true when only one rear wheel is in-
volved. However, when both rear wheels are affected,
the master cylinder or proportioning valve could be
at fault.
BRAKES DO NOT HOLD AFTER DRIVING
THROUGH DEEP WATER PUDDLES
This condition is generally caused by water soaked
lining. If the lining is only wet, it can be dried by
driving with the brakes lightly applied for a mile or
two. However, if the lining is both wet and dirty, dis-
assembly and cleaning will be necessary.
BRAKE FLUID CONTAMINATION
There are two basic causes of brake fluid contami-
nation. The first involves allowing dirt, debris, or
other liquid materials to enter the cylinder reservoirs
JBRAKES 5 - 9