Speed Control System Description And Operation - Jeep Cherokee 2000 Service Manual

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DESCRIPTION AND OPERATION
SPEED CONTROL SYSTEM . . . . . . . . . . . . . . . . . 1
SPEED CONTROL SERVO. . . . . . . . . . . . . . . . . . . 2
SPEED CONTROL SOLENOID CIRCUITS . . . . . . . 2
SPEED CONTROL SWITCHES . . . . . . . . . . . . . . . 2
BRAKE LAMP SWITCH. . . . . . . . . . . . . . . . . . . . . 3
SERVO CABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
VACUUM RESERVOIR . . . . . . . . . . . . . . . . . . . . . 3
VEHICLE SPEED SENSOR (SPEED CONTROL
OPERATION) . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
DESCRIPTION AND OPERATION
SPEED CONTROL SYSTEM
DESCRIPTION
The speed control system is electronically con-
trolled and vacuum operated. Electronic control of
the speed control system is integrated into the Pow-
ertrain Control Module (PCM). The controls consist
of two steering wheel mounted switches. The
switches are labeled: ON/OFF, RES/ACCEL, SET,
COAST, and CANCEL.
The system is designed to operate at speeds above
30 mph (50 km/h).
WARNING: THE USE OF SPEED CONTROL IS NOT
RECOMMENDED WHEN DRIVING CONDITIONS DO
NOT PERMIT MAINTAINING A CONSTANT SPEED,
SUCH AS IN HEAVY TRAFFIC OR ON ROADS THAT
ARE WINDING, ICY, SNOW COVERED, OR SLIP-
PERY.
OPERATION
When speed control is selected by depressing the
ON switch, the PCM allows a set speed to be stored
in PCM RAM for speed control. To store a set speed,
depress the SET switch while the vehicle is moving
at a speed between 35 and 85 mph. In order for the
speed control to engage, the brakes cannot be
applied, nor can the gear selector be indicating the
transmission is in Park or Neutral.
The speed control can be disengaged manually by:
• Stepping on the brake pedal
• Depressing the OFF switch
• Depressing the CANCEL switch.
SPEED CONTROL SYSTEM
TABLE OF CONTENTS
page
SPEED CONTROL SYSTEM
DIAGNOSIS AND TESTING
ROAD TEST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
VACUUM SUPPLY TEST . . . . . . . . . . . . . . . . . . . . 4
REMOVAL AND INSTALLATION
SPEED CONTROL SERVO. . . . . . . . . . . . . . . . . . . 5
SPEED CONTROL SWITCH. . . . . . . . . . . . . . . . . . 5
SERVO CABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
VACUUM RESERVOIR . . . . . . . . . . . . . . . . . . . . . 6
SPECIFICATIONS
TORQUE CHART . . . . . . . . . . . . . . . . . . . . . . . . . . 7
• Depressing the clutch pedal (if equipped).
NOTE: Depressing the OFF switch or turning off
the ignition switch will erase the set speed stored
in the PCM.
For added safety, the speed control system is pro-
grammed to disengage for any of the following condi-
tions:
• An indication of Park or Neutral
• A rapid increase rpm (indicates that the clutch
has been disengaged)
• Excessive engine rpm (indicates that the trans-
mission may be in a low gear)
• The speed signal increases at a rate of 10 mph
per second (indicates that the coefficient of friction
between the road surface and tires is extremely low)
• The speed signal decreases at a rate of 10 mph
per second (indicates that the vehicle may have
decelerated at an extremely high rate)
Once the speed control has been disengaged,
depressing the RES/ACCEL switch (when speed is
greater than 30 mph) restores the vehicle to the tar-
get speed that was stored in the PCM.
While the speed control is engaged, the driver can
increase the vehicle speed by depressing the RES/AC-
CEL switch. The new target speed is stored in the
PCM when the RES/ACCEL is released. The PCM
also has a "tap-up feature in which vehicle speed
increases at a rate of approximately 2 mph for each
momentary switch activation of the RES/ACCEL
switch.
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