Page 417 of 1502
8H - 2
VEHICLE SPEED CONTROL SYSTEM
• TO RESUME: After disengaging the speed control
system by tapping the brake or clutch pedal, push
the RESUME/ACCEL button to return vehicle to the
previously set speed. TO ACCELERATE: While speed control is en
gaged, hold the RESUME/ACCEL button depressed and release at a new desired speed. This will allow
the vehicle to continuously accelerate and set at a
higher speed setting.
TAP-UP: When the speed control system is en
gaged, tapping the RESUME/ACCEL button will in
crease the speed setting by 2 mph (3 km/h). The system will respond to multiple tap-ups.
TO ACCELERATE for PASSING: Depress the
accelerator as you would normally. When the pedal
is released the vehicle will return to the speed set
ting in memory.
SERVO
CONNECTOR
J918H-20
Fig.
2
Speed
Control
System
—Diesel
Engine
Page 418 of 1502

VEHICLE
SPEED
CONTROL
SYSTEM
8H - 3
GAS
ENGINE
warnings the usi of THE
SPEED
control is NOT recommended when
DRIVING
CONDITIONS
DO not
PERMIT
maintaining
A
constant
SPEED, SUCH
AS
HEAVY
TRAFFIC
©r on
ROADS
THAT ARE
WINDING, ICY, SNOW COVERED
OR
SLIPPERY*
START
ENGINE
r
ACCELERATE
VEHICLE TO DESIRED SPEED
SPEED
CONTROL
ENGAGES
WHEN
mmm is
STARTED
PUSH
ON/OFF
BUTTON
TO "ON"
POSITION.
E
FAULTY
ELECTRICAL CIRCUIT*
SPEED
CONTROL ENGAGES
WITHOUT
PUSHING
THE
"SET/DECEL"
BUTTON
PUSH
AND
RELEASE
"SET/DECEL'
'
BUTTON
FAULTY
ELECTRICAL CIRCUIT* DEFECTIVE SERVO
i
DEFECTIVE SERVO
REMOVE
FOOT
FROM
ACCELERATOR.
SPEED
SHOULD
BE
CONTROLLED
T
1
i
1
*
NO
WEED
CONTROL
WHEN
SET/DECEL
BUTTON IS
PRESSED
AND RELEASED
HUNTING
SURGE
OR
SPEED
VARIATIONS AT
LOW
SPEEDS
EXCESSIVE
SAG
ON
HILLS
OR
IN
TRAILER TOWING
SPEED
SETTING AFTER
LOCK-IN,
TOO
HIGH
C3«t LOW
4 *
FUSE
BLOWN
LOCK-UP
TORQUE CONVERTER
ROUGHNESS
ENGINE
PERFORMANCE
VACUUM LEAK
# f
t f
NO
VACUUM
AT
SERVO
AMPLIFICATION
OF ENGINE
SURGE
VACUUM
LEAK
DEFECTIVE SERVO
1
f
it
t
t
SPEED
CONTROL
THROTTLE
CABLE
DISCONNECTED
DEFECTIVE SERVO
EXCESSIVE
LOAD
MAY
REQUIRE MANUAL
ASSISTANCE
ON
HILLS DEFECTIVE
CABLE
i
f
f • *
IMPROPER
STOP LAMP
AND
SPEED CONTROL SWITCH ADJUSTMENT DEFECTIVE
CABLE
DEFECTIVE VACUUM
RESERVOIR
(CHECK VALVE) DEFECTIVE
VACUUM RESERVOIR
1
f
*
FAULTY
ELECTRICAL CIRCUIT* DEFECTIVE
ENGINE
CONTROLLER
DEFECTIVE SERVO
* TESTS AND
ADJUSTMENTS
ARE DESCRIBED
IN
APPROPRIATE
SECTION
OF SERVICE
MANUAL.
DEFECTIVE VACUUM
RESERVOIR
J918H-7
Page 419 of 1502

8H - 4 VEHICLE
SPEED
CONTROL SYSTEM
GAS
ENGINE
CONTINUED
UNIT
DISENGAGES
ON ROUGH ROAD
IMPROPER
ADJUSTMENT OF STOP LAMP AND SPEED
CONTROL SWITCH*
FAULTY
ELECTRICAL CIRCUIT
£
ENGINE DOES
NOT RETURN TO NORMAL IDLE
SPEED
CONTROL
THROTTLE
CABLE
KINKED OR DAMAGED
STANDARD
THROTTLE
LINKAGE FAULTS 1
DRIVE VEHICLE OVER
ROUGH ROAD
TAP BRAKE PEDAL
LIGHTLY,
SPEED
CONTROL SHOULD
DISENGAGE
SPEED
CONTROL
DISENGAGES
PUSH RESUME/ACCEL SWITCH VEHICLE
SHOULD RESUME PREVIOUSLY
MEMORIZED SPEED
VEHICLE RESUMES
SPEED
DEPRESS
BRAKE
PEDAL,
SPEED CONTROL
SHOULD DISENGAGE NO SYSTEM
DISENGAGEMENT
WHEN MAKE PEDAL
IS
DEPRESSED
DEFECTIVE OR
IMPROPERLY ADJSUTED
STOP LAMP AND
SPEED
CONTROL SWITCH
y
f
SPEED
CONTROL
THROTTLE
CABLE
KINKED OR DAAAAGED
1
FAULTY
ELECTRICAL CIRCUIT*
f
DEFECTIVE SERVO NO RESUME WHEN
BUTTON
IS
PRESSED
SPEED
CONTROL
DISENGAGES
DEFECTIVE SWITCH
FAULTY
ELECTRICAL CIRCUIT* NO SYSTEM
DISENGAGE
WHEN BRAKE PEDAL IS
DEPRESSED
SPEED
CONTROL
SYSTEM OK
1
f
DEFECTIVE ENGINE CONTROLLER
1
FAULTY
ELECTRICAL CIRCUIT*
r
STICKY BRAKE SWITCH RESUM
ISPO
BELOW
2
E
SPEED
SSIBLE
10
M.P.H.
y t
DEFECTIVE DISTANCE
SENSOR
y f
DEFECTIVE
ENGINE CONTROLLER
J928H-14
Page 420 of 1502

•
^ ^ VEHICLE
SPEED
CONTROL
SYSTEM
8H - I
WARNING:
THE USE OF THE
SPEED
CONTROL
IS
NOT
RECOMMENDED
WHEN DRIVING
CONDITIONS
DO NOT PERMIT MAINTAINING
A
CONSTANT
SPEED,
SUCH AS HEAVY
TRAFFIC
OR ON
ROADS
THAT
ARE WINDING,
ICY,
SNOW
COVERED
OR
SLIPPERY*
SPEED
CONTROL
ENGAGES
WITHOUT PUSHING THE
"SET/DECEL"
BUTTON
±
FAULTY
ELECTRICAL CIRCUIT*
±
DEFECTIVE
SERVO
START ENGINE
ACCELERATE
VEHICLE TO DESIRED SPEED
PUSH
ON/OFF
BUTTON
TO "ON" POSITION.
PUSH
AND
RELEASE
"SET/DECEL"
BUTTON
REMOVE
FOOT
FROM
ACCELERATOR.
SPEED
SHOULD BE CONTROLLED
SPEED
CONTROL
ENGAGES
WHEN
ENGINE IS STARTED
FAULTY
ELECTRICAL
CIRCUIT*
T
DEFECTIVE SERVO
NO
SPEED
CONTROL WHEN
SET/DECEL
BUTTON
IS
PRESSED
AND
RELEASED
FUSE
BLOWN
NO VACUUM AT
SERVO
T
SPEED
CONTROL
THROTTLE
CABLE DISCONNECTED
IMPROPER
STOP LAMP AND SPEED CONTROL SWITCH ADJUSTMENT
FAULTY
ELECTRICAL CIRCUIT*
T
DEFECTIVE SERVO
DEFECTIVE
VACUUM PUMP
HUNTING
SURGE
OR
SPEED
VARIATIONS AT LOW
SPEEDS
I
LOCK-UP
TORQUE CONVERTER
ROUGHNESS
AMPLIFICATION OF ENGINE
SURGE
DEFECTIVE SERVO
DEFECTIVE
CABLE
DEFECTIVE
ENGINE CONTROLLER
EXCESSIVE
SAG
ON HILLS OR
IN TRAILER
TOWING
ENGINE
PERFORAAANCE
VACUUM
LEAK
EXCESSIVE
LOAD MAY
REQUIRE
MANUAL
ASSISTANCE
ON HILLS
DEFECTIVE
VACUUM PUMP
SPEED
SETTING AFTER
LOCK-IN,
TOO
HIGH
OR TOO LOW
T
VACUUM LEAK
DEFECTIVE SERVO DEFECTIVE
CABLE
T
DEFECTIVE
VACUUM PUMP
REFER
TO GROUP 5 - BRAKES
FOR VACUUM PUMP DIAGNOSIS.
"TEST AND ADJUSTMENTS ARE DESCRIBED IN APPROPRIATE SECTION OF SERVICE MANUAL.
J928H-15
DIESEL
ENGINE
Page 421 of 1502

- 6
VEHICLE SPEED CONTROL SYSTEM
• £
UNIT
DISENGAGES
ON ROUGH ROAD
IMPROPER
ADJUSTMENT
OF
STOP LAMP AND SPEED
CONTROL SWITCH*
i
FAULTY
ELECTRICAL CIRCUIT
ENGINE DOES
NOT RETURN
TO
NORMAL IDLE
SPEED
CONTROL
THROTTLE
CABLE
KINKED OR DAAAAGED
STANDARD
THROTTLE
LINKAGE FAULTS
NO RESUME WHEN
BUTTON
IS
PRESSED
DRIVE VEHICLE OVER
ROUGH ROAD
±
TAP BRAKE PEDAL
LIGHTLY,
SPEED
CONTROL SHOULD
DISENGAGE
SPEED
CONTROL
DISENGAGES
PUSH RESUME/ACCEL SWITCH VEHICLE
SHOULD RESUME PREVIOUSLY
MEMORIZED SPEED
VEHICLE RESUMES
SPEED
DEPRESS
BRAKE
PEDAL,
SPEED CONTROL
SHOULD DISENGAGE NO SYSTEM
DISENGAGEMENT
WHEN MAKE PEDAL
IS
DEPRESSED
DEFECTIVE OR
IMPROPERLY ADJSUTED STOP LAMP
AND
SPEED
CONTROL SWITCH
1
1
SPEED
CONTROL
THROTTLE
CABLE
KINKED
OR
DAAAAGED
1
FAULTY
ELECTRICAL CIRCUIT*
1
DEFECTIVE SERVO
SPEED
CONTROL
DISENGAGES
DEFECTIVE SWITCH
FAULTY
ELECTRICAL CIRCUIT*
1
NO SYSTEM
DISENGAGE
WHEN BRAKE PEDAL
IS
DEPRESSED
SPEED
CONTROL
SYSTEM
OK
1
r
DEFECTIVE ENGINE CONTROLLER
* r
FAULTY
ELECTRICAL CIRCUIT*
r
STICKY BRAKE SWITCH RESUM
ISPO
BELOW*
E
SPEED
SSIBLE
10
M.P.H.
1
DEFECTIVE DISTANCE
SENSOR
f
DEFECTIVE
ENGINE CONTROLLER
J928H-14 DIESEL ENGINE CONTINUED
Page 422 of 1502

•
VEHICLE
SPEED
CONTROL SYSTEM
8H - 7
TEST
PROCEDURES
INDEX
page
Checking
for
Diagnostic
Trouble
Code
7
General
Information
7
Inoperative
System
7
Road
Test
7
Speed
Control
Cable Adjustment—Diesel Engine
. 9
Speed
Control
Cable
Attachment
10
GENERAL
INFORMATION
Before starting diagnosis and repair procedures for
a speed control malfunction, verify that the speed
control wire harness is properly connected to all con nectors. Refer to Diagnosis Chart.
ROAD
TEST
Road test vehicle to verify reports of speed control
system malfunction. The road test should include at
tention to the speedometer. Speedometer operation should be smooth and without flutter 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 deficiencies should be corrected before proceeding.
INOPERATIVE SYSTEM
If road test verifies a system problem and the
speedometer operates properly, check for:
• loose electrical and vacuum connections at the
servo.
• check for correct installation of the vacuum check
valve in the hose from servo to vacuum source (Gas
Engine Only). The word VAC on the valve must
point toward the vacuum source. • corrosion that should be removed from electrical
terminals and a light coating of Mopar Multi-Pur
pose Grease, or equivalent, applied. • secure attachment of both ends of speed control ca
ble.
CHECKING
FOR DIAGNOSTIC TROUBLE CODE
(1) When trying to verify a speed control system
electrical problem, use a DRB II Scan Tool to find
the cause. Refer to Powertrain Diagnostic Procedures manual. If the DRBII is not available, the Diagnostic Trou
ble Code (DTC) may be determined with the follow ing method: (a) With key inserted in ignition switch, cycle
switch to ON position 3 times. On third cycle, leave
switch in ON position. (b) After switch has been cycled 3 times, observe
Malfunction Indicator Lamp (CHECK ENGINE) on instrument cluster. If a DTC is present, the code
page
Speed
Control
Cable Attachment—Servo
10
Stop Lamp Switch Test
9
Vacuum Supply Test
....................... 9
Vehicle Speed
Control
Switch Test
. 9
Vehicle Speed
Control
System
Electrical
Tests
... 7
Vehicle Speed Sensor Test
7
will be displayed in a series of flashes representing
digits.
Three flashes in rapid succession, a slight
pause, then 4 flashes in rapid succession would in dicate DTC 34.
(2) If a DTC 34 is observed, perform the tests in
the sections Electrical Tests at Servo and Electrical
Tests at Powertrain Control Module.
If a DTC 15 is observed, perform the test for a
faulty Vehicle Speed Sensor.
(3) If a fault code 11 is observed (Diesel only), per
form the test for a faulty engine speed sensor. Refer
to the Powertrain Diagnostics Procedures Manual.
(4) Correct any problems found when performing
these tests and recheck for DTC if changes were made.
VEHICLE SPEED SENSOR TEST
For testing of the Vehicle Speed Sensor and related
components refer to the Powertrain Diagnostic Proce
dures manual.
VEHICLE SPEED CONTROL SYSTEM ELECTRICAL
TESTS
Vehicle speed control systems may be tested using
two different methods. One involves the use of the DRBII Scan Tool. If this test method is desired,
please refer to the Powertrain Diagnostic Procedures manual. The other test method uses a voltmeter. The volt
meter method is described in the following tests.
If any information is needed concerning wiring, re
fer to Group 8W - Wiring Diagrams.
CAUTION:
When test probing
for
voltage
or
continuity
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.
ELECTRICAL
TESTS
AT
SERVO
(1) Turn ignition switch to ON position.
(2) Push speed control switch to ON position.
(3) Connect the negative lead of a voltmeter to a
good chassis ground near the servo.
Page 423 of 1502

8H - 8
VEHICLE SPEED CONTROL SYSTEM
• (4) Disconnect the 4-way connector going to the
servo (Figs. 1 and 2), The blue wire with the red
tracer of the main harness 4-way connector should
read approximately battery voltage. If not, check for loose connections, brake switch adjustment or, repair
the main harness as necessary.
(5) Connect a jumper wire between the male and
female terminals of the blue wire with red tracer.
The other 3 male terminals from the servo should show battery voltage. If not, replace the servo. (6) Turn ignition OFF. Using an ohmmeter, con
nect one lead to a good body ground. Touch the other
lead to the black (BK) wire terminal in the 4-way
connector of the main harness. The meter should
show continuity. If not, repair the ground circuit as
necessary. A
VACUUM
y~
HOSE
J918H-24
Fig.
1 Servo And Harness Connector—Gas
Engine—Typical
ELECTRICAL TESTS AT POWERTRAIN CONTROL MODULE
(1) Unplug 60-way connector from Powertrain Con
trol Module, located on the left fender (Fig. 3).
(2) Connect negative lead of voltmeter to a good
body ground near the module. (3) For the following tests, the ignition switch
must be in the ON position. Refer to Fig. 4 for con
troller terminal locations. Touch the positive lead of
the voltmeter to the terminal in cavity number 33.
With the speed control switch in the OFF position,
the voltmeter should read 0 volts. With the speed
control switch in the ON position, the voltmeter should read battery voltage. If not, repair the main
harness as necessary.
(4) Touch the positive lead of the voltmeter to the
terminal in cavity number 53. As in step (3), the J918H-25
Fig. 2 Servo And Harness Connector—Diesel Engine PCM
MOUNTING
BOLTS
PCM CONNECTOR CONNECTOR MOUNTING BOLT
J9314-165
Fig.
3 Powertrain Control
Module
and
Connector
Location
voltmeter should read 0 volts with the switch in the OFF position and battery voltage with the switch in
the ON position. (5) Touch the positive lead of the voltmeter to the
terminal in cavity number 48. With the speed control switch in the OFF position, the voltmeter should
read 0 volts. With the switch in the ON position, the voltmeter should read battery voltage. Pressing the SET button should cause the voltmeter to change
Page 424 of 1502
![DODGE TRUCK 1993 Service Repair Manual
VEHICLE
SPEED
CONTROL SYSTEM
8H - 9
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RR8HC DODGE TRUCK 1993 Service Repair Manual
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SPEED
CONTROL SYSTEM
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SPEED
CONTROL SYSTEM
8H - 9
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Fig.
4 Powertrain Control Module 60-Way Connector
Shown from Terminal End
from battery voltage to 0 volts for as long as the switch is held. If not, perform the speed control
switch test. If the switch is not at fault, then check
the main harness and repair as necessary.
(6) Touch the positive lead of the voltmeter to the
terminal in cavity number 50. The voltmeter should read 0 volts with the speed control switch in either
the OFF or ON position. With switch in either RE SUME or SET position, the voltmeter should read
battery voltage. If not, perform the speed control switch test. If the switch is not at fault, then check
the main harness and repair as necessary.
(7) Touch the positive lead of the voltmeter to the
terminal in cavity number 49. The voltmeter should read 0 volts with the switch in the OFF position.
With the switch in the ON position, the voltmeter should read battery voltage. The voltmeter will con
tinue to read battery voltage when either the SET or
RESUME switch is pressed. If not, perform the speed control switch test. If the switch is not at fault, then
check the main harness and repair as necessary . (8) Turn key OFF. Using an ohmmeter, connect
one lead to a good body ground and touch the other
lead to the terminal in cavity number 29. With the
brake pedal released, the meter should show continu ity. When the pedal is depressed, the meter should
show open circuit.
VEHICLE
SPEED
CONTROL SWITCH TEST
To check the switch, remove the switch from its
mounting position. Use an ohmmeter and refer to the
Switch Continuity Chart to determine if continuity is
correct. If there is no continuity at any one of the
switch positions, replace the switch.
STOP
LAMP SWITCH TEST
(1) Disconnect connector at stop lamp switch. Us
ing an ohmmeter, continuity may be checked at
switch side of connector as follows (Fig. 5): (a) With brake pedal released, there should be:
• continuity between black (BK) and white with
pink tracer (WT/PK) wires
• continuity between yellow with red tracer (YL/RD) and dark blue with red tracer (DB/RD) wires
• No continuity between pink (PK) and white (WT)
wires.
SPEED CONTROL SWITCH CONTINUITY
CHART
CONNECTOR
TERMINAL
END
JE
El
SWITCH
SPEED
CONTROL
SWITCH
CONTINUITY
SWITCH!
rea?!®^
CONTINUITY
BETWEEN
OFF PIN 1
AND PIN 4
ON PIN
1 AND PIN 4
PIN 1
AND PIN 2
PIN
2 AND PIN 4
ON
AND
SET PIN
1
AN D
PIN 2
ON
AND
RESUME PIN
1 AND PIN 3
J928H-4
(b) With brake pedal depressed, there should be:
• continuity between pink (PK) and white (WT)
wires.
• No continuity between black (BK) and white with
pink tracer (WT/PK) wires.
• No continuity between yellow with red tracer (YL/
RD) and dark blue with red tracer (DB/RD) wires. (2) If the above results are not obtained, the stop
lamp switch is defective or out of adjustment.
Stop lamp switch adjustment is detailed in Group 5 -
Brakes.
VACUUM SUPPLY TEST
(1) Disconnect vacuum hose at the servo and in
stall a vacuum gauge in the hose (Fig. 6). (2) Start engine and observe gauge at idle. Vac
uum gauge should read at least ten inches of mer
cury. (3) If vacuum does not meet this requirement,
check for vacuum leaks or poor engine performance.
SPEED
CONTROL
CABLE
ADJUSTMENT-DIESEL
ENGINE
(1) The gap between the end of the slot on the ca
ble and the bellcrank pin must be as small as possi
ble (0 to 1mm) without moving the throttle. If gap is not correct, remove adjustment clip. Push protective