Overshoot/Undershoot On Speed Control Set; Powertrain Control Module (Pcm); Speed Control Servo; Removal And Installation - Jeep 1997 Grand Cherokee Service Manual

SERVO MOUNTING NUTS (2)
SERVO CABLE
8H - 6 VEHICLE SPEED CONTROL SYSTEM
DIAGNOSIS AND TESTING (Continued)
The engine must be started and running for the
following voltage tests.
(1) Start engine.
(2) Disconnect 4–way electrical connector at servo
(Fig. 2).
(3) Turn speed control switch to ON position.
(4) Check for battery voltage at pin–3 of wiring
harness 4–way connector (Fig. 3). This is the 12 volt
feed from the stoplamp switch. When the brake pedal
is depressed, voltage should not be present at pin–3.
If voltage is not present with brake pedal not
depressed, check for continuity between servo and
stop lamp switch. Also check stop lamp switch
adjustment. Refer to Group 5, Brakes for procedures.
(5) Connect a small gauge jumper wire between
the disconnected servo harness 4–way connector
pin–3, and pin–3 on the servo. Check for battery volt-
age at pins–1, 2 and 4 of the servo. If battery voltage
is not at these pins, replace the servo.
Fig. 2 Servo Electrical Connector Location
(6) Turn ignition switch to OFF position. Check for
continuity between
4–way connector pin–4 and a good ground. There
should be continuity. If not OK, repair open circuit to
ground as required.

POWERTRAIN CONTROL MODULE (PCM)

For complete PCM diagnosis of the speed control
system, refer to the DRB scan tool and the appropri-
ate Powertrain Diagnostic Procedures service man-
ual.
OVERSHOOT/UNDERSHOOT ON SPEED CONTROL
SET
If the operator repeatedly presses and releases the
set button with their foot off of the accelerator (a "lift
foot set" to begin speed control operation), the vehicle
disconnected servo
Fig. 3 Servo 4–Way Harness Connector
may accelerate and exceed the desired set speed by
up to 5 MPH (8 km/h) and then decelerate to less
than the desired set speed before finally achieving
the desired set speed.
The Speed Control has an adaptive strategy that
compensates for vehicle-to-vehicle variations in speed
control cable lengths. When the speed control is set
with the vehicle operators foot off of the accelerator
pedal, the speed control thinks there is excessive
speed control cable slack and adapts. If the lift foot
sets are continually used, the speed control over-
shoot/undershoot condition will develop.
To "unlearn" the overshoot/undershoot condition,
the vehicle operator has to press and release the set
button while maintaining the desired set speed with
the accelerator pedal (not decelerating or accelerat-
ing), and then turn the cruise control switch to the
OFF position (or press the CANCEL button if
equipped) after waiting 10 seconds. This procedure
must be performed approximately 10–15 times to
completely unlearn the overshoot/undershoot condi-
harness
tion.

REMOVAL AND INSTALLATION

SPEED CONTROL SERVO

REMOVAL
(1) Disconnect negative battery cable at battery.
(2) Disconnect vacuum hose at servo (Fig. 4).
(3) Unplug electrical connector at servo (Fig. 4).
(4) Remove 2 mounting nuts holding servo cable
sleeve to bracket (Fig. 4).
(5) Pull speed control cable sleeve away from servo
to expose cable retaining clip.
(6) Block throttle to full open position.
PIN 3
PIN 2
PIN 1
ZG