Jeep XJ. Manual — part 112
ing/air-conditioning system. The vacuum reservoir
cannot be repaired and must be replaced if faulty.
VEHICLE SPEED SENSOR (SPEED CONTROL
OPERATION)
DESCRIPTION
The Vehicle Speed Sensor (VSS) is mounted to an
adapter near the transmission output shaft. The sen-
sor is driven through the adapter by a speedometer
pinion gear.
OPERATION
The VSS is a pulse generator. The VSS pulse sig-
nal to the speedometer/odometer is monitored by the
PCM speed control circuitry to determine vehicle
speed and to maintain speed control set speed.
DIAGNOSIS AND TESTING
ROAD TEST
Perform a vehicle road test to verify reports of
speed control system malfunction. The road test
should include attention to the speedometer. Speed-
ometer operation should be smooth and without flut-
ter at all speeds.
Flutter in the speedometer indicates a problem
which might cause surging in the speed control sys-
tem. The cause of any speedometer problems should
be corrected before proceeding. Refer to Group 8E,
Instrument Panel and Gauges for speedometer diag-
nosis.
If a road test verifies a system problem and the
speedometer operates properly, check for:
• A Diagnostic Trouble Code (DTC). If a DTC
exists, conduct tests per the Powertrain Diagnostic
Procedures service manual.
• A misadjusted brake (stop) lamp switch. This
could also cause an intermittent problem.
• Loose, damaged or corroded electrical connec-
tions at the servo. Corrosion should be removed from
electrical terminals and a light coating of Mopar
MultiPurpose Grease, or equivalent, applied.
• Leaking vacuum reservoir.
• Loose or leaking vacuum hoses or connections.
• Defective one-way vacuum check valve.
• Secure attachment of both ends of the speed con-
trol servo cable.
• Smooth operation of throttle linkage and throttle
body air valve.
• Failed speed control servo. Do the servo vacuum
test.
CAUTION: When test probing for voltage or conti-
nuity at electrical connectors, care must be taken
not to damage connector, terminals or seals. If
these components are damaged, intermittent or
complete system failure may occur.
VACUUM SUPPLY TEST
(1) Disconnect vacuum hose at speed control servo
and install a vacuum gauge into the disconnected
hose.
(2) Start engine and observe gauge at idle. Vac-
uum gauge should read at least ten inches of mer-
cury.
(3) If vacuum is less than ten inches of mercury,
determine source of leak. Check vacuum line to
engine for leaks. Also check actual engine intake
manifold vacuum. If manifold vacuum does not meet
this requirement, check for poor engine performance
and repair as necessary.
(4) If vacuum line to engine is not leaking, check
for leak at vacuum reservoir. To locate and gain
access to reservoir, refer to Vacuum Reservoir Remov-
al/Installation in this group. Disconnect vacuum line
at reservoir and connect a hand-operated vacuum
pump to reservoir fitting. Apply vacuum. Reservoir
vacuum should not bleed off. If vacuum is being lost,
replace reservoir.
(5) Verify operation of one-way check valve and
check it for leaks.
(a) Locate one-way check valve. The valve is
located in vacuum line between vacuum reservoir
and engine vacuum source. Disconnect vacuum
hoses (lines) at each end of valve.
(b) Connect a hand-operated vacuum pump to
reservoir end of check valve. Apply vacuum. Vac-
uum should not bleed off. If vacuum is being lost,
replace one-way check valve.
(c) Connect a hand-operated vacuum pump to
vacuum source end of check valve. Apply vacuum.
Vacuum should flow through valve. If vacuum is
not flowing, replace one-way check valve. Seal the
fitting at opposite end of valve with a finger and
apply vacuum. If vacuum will not hold, diaphragm
within check valve has ruptured. Replace valve.
8H - 4
SPEED CONTROL SYSTEM
XJ
DESCRIPTION AND OPERATION (Continued)
REMOVAL AND INSTALLATION
SPEED CONTROL SERVO
REMOVAL
(1) Disconnect negative battery cable at battery.
(2) Disconnect vacuum line at servo (Fig. 1).
(3) Disconnect electrical connector at servo.
(4) Disconnect servo cable at throttle body. Refer to
Servo Cable Removal/Installation.
(5) Remove 2 mounting nuts holding servo cable
sleeve to bracket (Fig. 2).
(6) Pull speed control cable sleeve and servo away
from servo mounting bracket to expose cable retain-
ing clip (Fig. 2) and remove clip. Note: The servo
mounting bracket displayed in (Fig. 2) is a typical
bracket and may/may not be applicable to this model
vehicle.
(7) Remove servo from mounting bracket. While
removing, note orientation of servo to bracket.
INSTALLATION
(1) Position servo to mounting bracket.
(2) Align hole in cable connector with hole in servo
pin. Install cable-to-servo retaining clip.
(3) Insert servo mounting studs through holes in
servo mounting bracket.
(4) Install servo mounting nuts and tighten to 8.5
N·m (75 in. lbs.).
(5) Connect vacuum line at servo.
(6) Connect electrical connector at servo.
(7) Connect servo cable to throttle body. Refer to
Servo Cable Removal/Installation.
(8) Connect negative battery cable to battery.
(9) Before
starting
engine,
operate
accelerator
pedal to check for any binding.
SPEED CONTROL SWITCH
WARNING: BEFORE ATTEMPTING TO DIAGNOSE,
REMOVE OR INSTALL ANY AIRBAG SYSTEM OR
RELATED STEERING WHEEL AND STEERING COL-
UMN COMPONENTS YOU MUST FIRST DISCON-
NECT AND ISOLATE THE BATTERY NEGATIVE
(GROUND) CABLE. WAIT 2 MINUTES FOR SYSTEM
CAPACITOR TO DISCHARGE BEFORE FURTHER
SYSTEM SERVICE. FAILURE TO DO SO COULD
RESULT IN ACCIDENTAL DEPLOYMENT AND POS-
SIBLE PERSONAL INJURY.
Fig. 1 Speed Control Servo Location
1 – R. F. FENDER
2 – SPEED CONTROL SERVO
3 – ELECTRICAL CONNECTOR
4 – MOUNTING BRACKET
5 – VACUUM LINE
Fig. 2 Servo Cable Clip Remove/Install—Typical
1 – SERVO MOUNTING NUTS (2)
2 – SERVO
3 – CABLE RETAINING CLIP
4 – SERVO CABLE AND SLEEVE
XJ
SPEED CONTROL SYSTEM
8H - 5
REMOVAL
(1) Disconnect and isolate negative battery cable
from battery.
(2) Remove airbag module. Refer to Group 8M,
Passive Restraint Systems.
(3) From underside of steering wheel, remove
speed control switch mounting screw (Fig. 3).
(4) Remove switch from steering wheel and unplug
electrical connector.
INSTALLATION
(1) Plug electrical connector into switch.
(2) Position switch to steering wheel.
(3) Install switch mounting screw and tighten to
1.5 N·m (14 in. lbs.) torque.
(4) Install airbag module. Refer to Group 8M, Pas-
sive Restraint Systems.
(5) Connect negative battery cable to battery.
SERVO CABLE
REMOVAL
(1) Disconnect negative battery cable at battery.
(2) Using finger pressure only, remove cable con-
nector by pushing connector off the throttle body
bellcrank pin (Fig. 4). DO NOT try to pull cable
connector off perpendicular to the bellcrank
pin. Connector will be broken.
(3) Two release tabs are located on sides of speed
control cable at cable bracket (Fig. 4). Squeeze tabs
together and push cable out of bracket.
(4) Unclip cable from cable guide at valve cover.
(5) Disconnect servo cable at servo. Refer to Speed
Control Servo Removal/Installation.
INSTALLATION
(1) Attach end of cable to speed control servo.
Refer to Speed Control Servo Removal/Installation.
(2) Install cable into cable bracket (snaps in).
(3) Install
cable
connector
at
throttle
body
bellcrank pin (snaps on).
(4) Clip cable to cable guide at valve cover.
(5) Connect negative battery cable to battery.
(6) Before
starting
engine,
operate
accelerator
pedal to check for any binding.
VACUUM RESERVOIR
REMOVAL
The vacuum reservoir is located behind right front
bumper end cap on vehicles equipped with LHD (Left
Hand Drive) (Fig. 5). It is located behind left front
bumper end cap on vehicles equipped with RHD
(Right Hand Drive).
(1) Remove front bumper end cap. Refer to Front
Bumper End Cap Removal/Installation.
(2) Remove vacuum line at reservoir (Fig. 6).
Fig. 3 Speed Control Switch Remove/Install
1 – MOUNTING SCREW
2 – SPEED CONTROL SWITCH
Fig. 4 Speed Control Servo Cable at Throttle Body
1 – ACCELERATOR CABLE
2 – OFF
3 – OFF
4 – THROTTLE BODY BELLCRANK
5 – SPEED CONTROL CABLE
6 – RELEASE TABS
7 – BRACKET
8H - 6
SPEED CONTROL SYSTEM
XJ
REMOVAL AND INSTALLATION (Continued)
(3) Remove 2 reservoir mounting screws.
(4) Remove reservoir from bumper bar.
INSTALLATION
(1) Position reservoir to bumper bar and install
mounting screws. Tighten screws to 8 N·m (72 in.
lbs.) torque.
(2) Install vacuum line to reservoir
(3) Install front bumper end cap. Refer to Front
Bumper End Cap Removal/Installation.
SPECIFICATIONS
TORQUE CHART
Description
Torque
Servo Mounting Bracket-to-Servo Nuts . . . 8.5 N·m
(75 in. lbs.)
Servo Mounting Bracket-to-Body Bolts . . . . . 2 N·m
(20 in. lbs.)
Speed Control Switch Mounting Screws . . . 1.5 N·m
(14 in. lbs.)
Vacuum Reservoir Mounting Bolts . . . . . . . . 8 N·m
(72 in. lbs.)
Fig. 5 Vacuum Reservoir Location
1 – BUMPER END CAP
2 – VACUUM RESERVOIR
Fig. 6 Vacuum Reservoir Removal/Installation
1 – VACUUM LINE
2 – RESERVOIR SCREWS
3 – VACUUM RESERVOIR
XJ
SPEED CONTROL SYSTEM
8H - 7
REMOVAL AND INSTALLATION (Continued)
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