Vehicle Speed Control System - Jeep 1996 Grand Cherokee Service Manual

ZJ

VEHICLE SPEED CONTROL SYSTEM

GENERAL INFORMATION
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . 1
DESCRIPTION AND OPERATION
POWERTRAIN CONTROL MODULE (PCM) . . . . 2
SERVO CABLE . . . . . . . . . . . . . . . . . . . . . . . . . . 2
SPEED CONTROL SERVO . . . . . . . . . . . . . . . . . . 1
SPEED CONTROL SWITCHES . . . . . . . . . . . . . . 1
STOP LAMP SWITCH . . . . . . . . . . . . . . . . . . . . . 1
VACUUM RESERVOIR . . . . . . . . . . . . . . . . . . . . 2
VEHICLE SPEED SENSOR . . . . . . . . . . . . . . . . . 2
DIAGNOSIS AND TESTING
ON-BOARD DIAGNOSTICS TEST . . . . . . . . . . . . 2
POWERTRAIN CONTROL MODULE (PCM) . . . . 7
ROAD TEST . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
SPEED CONTROL ELECTRICAL TEST . . . . . . . . 6
GENERAL INFORMATION
INTRODUCTION
The vehicle speed control system is electronically
controlled and vacuum operated. The system is
designed to operate between approximately 35 and
85 mph (56 and 137 km/h). Following are general
descriptions of the major components in the speed
control system. Refer to Group 8W, Wiring Diagrams
for complete circuit descriptions and wiring dia-
grams.
DESCRIPTION AND OPERATION
SPEED CONTROL SERVO
The speed control servo is located in the engine
compartment, mounted to a bracket on the right
inner fender. The servo unit consists of a solenoid
valve body, a vacuum servo and the mounting
bracket. The PCM controls the solenoid valve body.
The solenoid valve body controls the application and
release of vacuum to the diaphragm of the vacuum
servo. The servo unit cannot be repaired and is ser-
viced only as a complete assembly.
SPEED CONTROL SWITCHES
Two separate speed control switch modules are
mounted on the steering wheel to the left and right
side of the driver's airbag module. Within the two
VEHICLE SPEED CONTROL SYSTEM
CONTENTS
page
SPEED CONTROL SERVO . . . . . . . . . . . . . . . . . . 6
SPEED CONTROL SWITCHES . . . . . . . . . . . . . . 6
STOP LAMP SWITCH . . . . . . . . . . . . . . . . . . . . . 6
VACUUM SUPPLY TEST . . . . . . . . . . . . . . . . . . . 6
VEHICLE SPEED SENSOR . . . . . . . . . . . . . . . . . 6
REMOVAL AND INSTALLATION
POWERTRAIN CONTROL MODULE . . . . . . . . . . 9
SERVO CABLE . . . . . . . . . . . . . . . . . . . . . . . . . . 8
SPEED CONTROL SERVO . . . . . . . . . . . . . . . . . . 7
SPEED CONTROL SWITCHES . . . . . . . . . . . . . . 8
STOP LAMP SWITCH . . . . . . . . . . . . . . . . . . . . . 8
VACUUM RESERVOIR . . . . . . . . . . . . . . . . . . . . 9
VEHICLE SPEED SENSOR . . . . . . . . . . . . . . . . . 9
SPECIFICATIONS
TORQUE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
switch modules, five momentary contact switches,
supporting seven different speed control functions
are used. The outputs from these switches are fil-
tered into one input. The Powertrain Control Module
(PCM) determines which output has been applied
through resistive multiplexing. The input circuit
voltage is measured by the PCM to determine which
switch function has been selected.
A speed control indicator lamp, located on the
instrument panel cluster is energized by the PCM via
the CCD Bus. This occurs when speed control system
power has been turned ON, and the engine is run-
ning.
The two switch modules are labeled: ON/OFF, SET,
RESUME/ACCEL, CANCEL and COAST. Refer to
the owner's manual for more information on speed
control switch functions and setting procedures. The
individual switches cannot be repaired. If one indi-
vidual switch fails, the switch module must be
replaced.
STOP LAMP SWITCH
Vehicles equipped with the speed control option use
a dual function stop lamp switch. The switch is
mounted in the same location as the conventional
stop lamp switch, on the brake pedal mounting
bracket under the instrument panel. The PCM mon-
itors the state of the dual function stop lamp switch.
Refer to Group 5, Brakes for more information on
stop lamp switch service and adjustment procedures.
8H - 1
page