Chrysler RAM TRUCK 2500 1994 Service Manual page 455

8H - 6 VEHICLE SPEED CONTROL SYSTEM
•
TEST PROCEDURES
INDEX
page
Checking for Diagnostic Trouble Code 6
General Information 6
Inoperative System 6
Road Test 6
Speed Control Cable Attachment 8
Speed Control Cable Attachment—Servo 9
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 i n the speedometer indicates a problem
which might cause surging i n the speed control sys­
tem. The cause of any speedometer deficiencies
should be corrected before proceeding.
INOPERATIVE SYSTEM
I f 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 i n 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-Purpose
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 scan tool to find the
cause. Refer to Powertrain Diagnostic Procedures
manual.
I f the DRB scan tool is not available, the diagnostic
trouble code (DTC) may be determined with the fol­
lowing method:
(a) With key inserted i n ignition switch, cycle
switch ON-OFF-ON-OFF-ON. On third cycle, leave
switch i n ON position.
(b) After switch has been cycled, observe mal­
function indicator lamp (Check Engine) on in-
page
Stop Lamp Switch Test 8
Vacuum Supply Test 8
Vehicle Speed Control Switch Test 8
Vehicle Speed Control System Electrical Tests 6
Vehicle Speed Sensor Test . . . . . . . . . . . . . . . . . . . 6
strument cluster. I f a DTC is present, the code will
be displayed i n a series of flashes representing dig­
its. Three flashes i n rapid succession, a slight
pause, then 4 flashes i n rapid succession would in­
dicate DTC 34.
(2) I f a DTC 34 is observed, perform the tests i n
the sections Electrical Tests at Servo and, Electrical
Tests at Powertrain Control Module.
I f a DTC 15 is observed, perform the test for a
faulty vehicle speed sensor.
(3) I f a fault code 11 is observed (diesel only), per­
form the test for a faulty engine speed sensor. Refer
to the Powertrain Diagnostic Procedures manual.
(4) Correct any problems found when performing
these tests and recheck for DTC i f 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
DRB scan tool. I f this test method is desired, refer
to the Powertrain Diagnostic Procedures manual.
The other test method uses a voltmeter. The volt­
meter method is described i n the following tests.
I f any information is needed concerning wiring, re­
fer to Group 8W - Wiring Diagrams.
CAUTION: When test probing for voltage or conti­
nuity at electrical connectors, care must be taken
not to damage connector, terminals, or s e a l s . If
these components are damaged, intermittent or
complete system failure may occur.
ELECTRICAL TESTS AT SERVO
Refer to Service Procedures for access to servo.
(1) Turn ignition switch to ON position.
(2) Push speed control switch to ON position.