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JX
DIAGNOSIS AND TESTING (Continued)
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
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-
tion.
SERVO VACUUM TEST
(1) Turn ignition switch to the ON position with-
out starting engine. Activate speed control ON
switch.
(2) Disconnect the four-way electrical connector
and the vacuum harness at the servo (Fig. 5).
(3) Connect a jumper wire from Pin 3 of the servo
to Pin 3 of the wire connector.
(4) Ground Pins 2 and 4 in the servo. Do not con-
nect pin 1.
(5) Connect a hand held vacuum pump to the vac-
uum nipple and apply 10 - 15 inches of vacuum.
(6) If servo pulls cables, replace servo.
(7) Ground Pin 1 on servo.
(8) Check that the throttle cable pulls in and holds
as long as the vacuum pump is connected. After one
minute, check if cable is still holding. If cable does
not hold replace the servo.
(9) Disconnect jumper from pin 3. Cable should
return to rest position. If not, replace servo.
(10) Connect 4 way electrical connector and vac-
uum harness to servo.
SPEED CONTROL SWITCH TEST
The speed control switches mounted on the steer-
ing wheel contain five switches and four resistors.
The PCM sends 5 volts through pin 41 to the speed
control switches. The input on pin 41 is responsible
CONNECTORS
FROM TERMINAL END
SHOWN
PIN 4
PIN 3
PIN 1
PIN 1
PIN 2
PIN 3
PIN 4
PIN 2
VEHICLE SPEED CONTROL SYSTEM
Fig. 5 Servo Harness Connector
Fig. 6 Speed Control Switch
for identifying the following: Resume/Accelerate, Set/
Coast, On, Off and Cancel. This is accomplished by
multiplexing. Multiplexing allows the PCM to iden-
tify more than one signal from a single wire. To
accomplish this, the speed control switch uses resis-
tors that cause different voltage signals at pin 41.
The 5-volt signal at pin 41 has no path to ground
when no buttons are depressed, allowing the PCM to
recognize the open circuit. When the ON, OFF switch
contacts are closed, the 5 volt signal is pulled
through a 15400 ohm resistor to ground providing a
voltage of 4.14 to 4.73 volts at pin 41. Once the PCM
recognizes the ON signal, the PCM provieds a bat-
tery voltage signal to the speed control servo through
pin 5 of the 80–way connector.
When the SET/COAST switch is depressed, a
momentary contact closes a path to ground through a
2,940 ohm resistor. This causes a voltage of approxi-
mately 1.99 to 3.20 volts at pin 41, indicating that
the SET/COAST switch has been depressed. When
the RES/ACCEL switch is depressed, a momentary
8H - 7
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