engine DODGE NEON 1999 Service Manual Online

INSTRUMENT PANEL AND SYSTEMS
CONTENTS
page page
GENERAL INFORMATION
INTRODUCTION......................... 1
DESCRIPTION AND OPERATION
DOME LAMP............................ 1
ELECTRONIC DIGITAL CLOCK.............. 1
INSTRUMENT CLUSTER................... 2
WARNING AND INDICATOR LAMPS......... 2
DIAGNOSIS AND TESTING
AIRBAG WARNING SYSTEM............... 2
BRAKE SYSTEM WARNING LAMP TEST...... 2
FOG LAMP SWITCH TEST................. 2
FUEL TANK SENDING UNIT TEST........... 3
HEADLAMP SWITCH TEST................. 3
HEATER A/C BLOWER SWITCH TEST........ 3
HEATER BLOWER SWITCH TEST............ 3
INDIVIDUAL GAUGE INOPERATIVE.......... 4
INSTRUMENT PANEL AND COMPONENTS.... 4
LOW OIL PRESSURE WARNING LAMP TEST . . 4
MULTIPLE GAUGE INOPERATIVE TEST....... 4
SEAT BELT REMINDER SYSTEM TEST....... 6
SENDING UNIT......................... 6
SERVICE ENGINE SOON INDICATOR......... 6
VEHICLE SPEED SENSOR TEST............. 6
REMOVAL AND INSTALLATION
ASH RECEIVER RETAINER AND LAMP....... 6
CENTER BEZEL.......................... 6
CIGAR LIGHTER RECEPTACLE.............. 6
CLUSTER LAMP......................... 7
CLUSTER PRINTED CIRCUIT BOARD........ 7CLUSTER.............................. 7
DOME LENS/LAMP....................... 8
FLOOR CONSOLE........................ 8
GAUGE................................ 8
GLOVE BOX DOOR/BIN................... 8
GLOVE BOX SWITCH/LAMP................ 9
HEADLAMP SWITCH..................... 9
HEATER A/C CONTROL BLOWER SWITCH . . . 10
HEATER A/C CONTROL LAMP............ 10
HEATER A/C CONTROL................... 9
HEATER CONTROL BLOWER SWITCH....... 10
IGNITION KEY LAMP.................... 10
INSTRUMENT PANEL.................... 10
LEFT TRIM PANEL...................... 10
ODOMETER............................ 10
RADIO................................ 12
REAR WINDOW DEFOGGER AND/OR FOG
LAMP SWITCH....................... 12
RIGHT TRIM PANEL..................... 12
SHIFTER KNOB......................... 13
STEERING COLUMN COVER LINER......... 13
STEERING COLUMN COVER.............. 13
STEERING COLUMN SHROUDS............ 13
TOP COVER AND CLUSTER BEZEL
REMOVAL........................... 14
TRANSMISSION RANGE INDICATOR LAMP . . 14
TRUNK LAMP/LENS..................... 14
VEHICLE SPEED SENSOR................ 14
GENERAL INFORMATION
INTRODUCTION
The purpose of the dash gauges and indicator
lamps is to keep the driver informed about the oper-
ating condition of the vehicle. If an abnormal condi-
tion occurs, the driver is informed by indicator lamp.
The driver can seek service before damage occurs.
Indicator lamps use ON/OFF switch functions for
operation, while gauges use a sending unit or sensor.
DESCRIPTION AND OPERATION
DOME LAMP
The Dome Lamp operates when a door is open or
when the headlamp switch is placed in courtesy posi-
tion.
ELECTRONIC DIGITAL CLOCK
The electronic digital clock is in the radio. The
clock and radio each use the display panel built into
the radio. A digital readout indicates the time in
hours and minutes whenever the ignition switch is in
the ON or ACC position.
PLINSTRUMENT PANEL AND SYSTEMS 8E - 1

When the ignition switch is in the OFF position, or
when the radio frequency is being displayed, time
keeping is accurately maintained.
The procedure for setting the clock varies slightly
with each radio. The correct procedure is described in
the individual radio operating instructions. Refer to
the Owner's Manual supplied with the vehicle.
INSTRUMENT CLUSTER
There are two conventional instrument cluster
assemblies available. The clusters electronically drive
the speedometer, odometer, and gauges (Fig. 1) and
(Fig. 2).
GAUGES
All gauges in the electronic clusters are the analog
type gauges. When the ignition switch is moved to
the OFF position, the cluster drives each gauge to its
lowest position.
WARNING AND INDICATOR LAMPS
The instrument cluster has warning lamps and
indicators for the following systems:
²Airbag
²Anti-lock Brakes (ABS) if equipped
²Brake warning
²Charging System
²Door Ajar
²High beam indicator
²Low oil pressure
²Malfunction indicator (service engine soon) lamp
²Right and left turn signals.
²Seat belt warning
DIAGNOSIS AND TESTING
AIRBAG WARNING SYSTEM
For testing of this system refer to Group 8M,
Restraint Systems.
BRAKE SYSTEM WARNING LAMP TEST
The brake warning lamp illuminates when the
parking brake is applied with ignition switch turned
to the ON position. The same lamp will also illumi-
nate if one of the two service brake systems fail the
when brake pedal is applied.
To test the system:
²As the ignition switch is turned to the start posi-
tion the lamp should light.
²Turn ignition switch to the ON position and
apply the parking brake. The lamp should light.
If lamp fails to light inspect for:
²A burned out lamp
²Loose, corroded or damaged socket
²A damaged circuit board
²A broken or disconnected wire at the switch
²Defective switch
To test the service brake warning system, refer to
Group 5, Brakes, Hydraulic System Control Valves.
FOG LAMP SWITCH TEST
(1) Remove the fog lamp switch. Refer to the Rear
Window Defogger and/or Fog Lamp Switch Removal.
(2) Using two jumper wires, connect Pin 2 and Pin
4 of the switch to battery voltage.
(3) Using a test lamp, connect the test lamp to Pin
3 as shown in (Fig. 3). Refer to (Fig. 4) for fog lamp
switch circuit.
(4) Push the fog lamp switch button. The test lamp
and the LED indicator on the front of the switch
should illuminate.
(5) If either the LED or the test lamp fails to illu-
minate, replace the switch.Fig. 1 Instrument Cluster Without Tachometer
Fig. 2 Instrument Cluster With Tachometer
Fig. 3 Fog Lamp Switch Test
8E - 2 INSTRUMENT PANEL AND SYSTEMSPL
DESCRIPTION AND OPERATION (Continued)

(2) Use a ohmmeter, and check continuity between
the terminals of the switch as shown in the Heater
Blower Test (Fig. 7).
(3) If switch fails any part of the continuity test,
other then Pin 1 to Pin 7, replace heater control. If
no continuity between Pin 1 to Pin 7 check the
lamps, replace if necessary.
INSTRUMENT PANEL AND COMPONENTS
CAUTION: Disconnect the battery negative cable
before servicing the instrument panel or compo-
nents. When power is required for test purposes,
connect battery cable for test only. Disconnect the
battery negative cable after test and before continu-
ing service procedures.
LOW OIL PRESSURE WARNING LAMP TEST
The low oil pressure warning lamp will illuminate
when the ignition switch is turned to the ON position
without engine running. The lamp also illuminates if
the engine oil pressure drops below a safe oil pres-
sure level.
To test the system, turn the ignition switch to the
ON position. If the lamp fails to light, inspect for a
broken or disconnected wire at the oil pressure
switch, located at the front of the engine (Fig. 8). If
the wire at the connector checks good, pull the con-
nector loose from the switch and with a jumper wire,
ground the connector to the engine. With the ignition
switch turned to the ON position, check the warning
lamp. If the lamp still fails to light, inspect for aburned out lamp or disconnected socket in the clus-
ter.
MULTIPLE GAUGE INOPERATIVE TEST
Test speedometer, tachometer and other gauges for
malfunction:
(1) Remove the cluster. Refer to Cluster Removal
and Installation.
(2) Check for ignition voltage at Pin J1-5 of the
cluster wire harness connector (Fig. 9) and (Fig. 10).
Check for battery voltage at Pin J1-6 of the connec-
tor. If no voltage, repair as necessary.
(3) Check Pin J1-8 of the connector for continuity
to ground. If no ground, repair as necessary.
(4) If the voltage and ground are OK, and the pins
or the connectors are not distorted, replace the
printed circuit board.
(5) Install cluster.
INDIVIDUAL GAUGE INOPERATIVE
FUEL GAUGE
(1) Disconnect the fuel gauge sending unit.
Fig. 7 Heater Blower Switch Test
Fig. 8 Oil Pressure Switch
Fig. 9 Cluster Wire Harness Connector
8E - 4 INSTRUMENT PANEL AND SYSTEMSPL
DIAGNOSIS AND TESTING (Continued)

(2) Turn the ignition switch to the ON position.
The fuel gauge should be at its lowest position. Turn
the ignition switch OFF.
(3) Ground fuel gauge sending unit connector Pin
3. Refer to Group 8W, Wiring Diagrams. Turn igni-
tion switch to the ON position. The fuel gauge should
be at its highest position. Turn ignition switch OFF
then ON, after a sending unit signal change to dis-
able the cluster electronic gauge dampening mecha-
nism.
(a) If OK, check the fuel gauge sending unit con-
nector for proper connection. If the connections are
OK, refer to Group 14 Fuel System for Fuel Level
Sensor Diagnosis.
(b) If not OK, connect the sending unit. Remove
the cluster and check for an open or short in the
sending unit wiring. The sending unit will be less
than 1080 ohms and greater than 50 ohms depend-
ing upon fuel level. If the sending unit wiring is
open or a short circuit, repair as necessary.
(c) If the sending unit wiring is OK, replace the
gauge assembly. If the condition persists, replace
the cluster printed circuit board.
FUEL GAUGE INCORRECTLY INDICATES
EMPTY
The fuel system uses both the instrument cluster
and the Powertrain Control Module (PCM) to moni-
tor the fuel level sending unit. If the PCM fuel mon-
itoring circuits senses an open circuit, the increased
circuit resistance will causes a false fuel gauge empty
reading. Check for continuity between cluster wire
harness connector Pin J2-10 and Pin 23 of the PCM(Fig. 9) and (Fig. 11). If there is no continuity, repair
as necessary. If there is continuity, refer to Fuel
Gauge test.
LOW FUEL WARNING CIRCUIT
The low fuel warning lamp receives its signal from
the fuel gauge drive circuit. Due to production varia-
tions, the point where the lamp illuminates, may
vary from 1/16 to 3/16 mark on the fuel gauge. There
is a built in time delay before the lamp illuminates.
This prevents the lamp from going on and off under
various road conditions.
(1) Verify that the fuel gauge is operating properly.
(2) Check the low fuel warning lamp assembly.
(3) If the lamp still does not function under a low
fuel condition replace the printed circuit board.
TACHOMETER CIRCUIT
(1) Remove the cluster. Refer to Cluster Removal.
(2) Check for battery voltage at Pin J1-6 of the
cluster wire harness connector (Fig. 9).
(3) With the ignition switch in the ON position,
check for battery voltage at Pin J1-5 connector.
(4) Check Pin J1-8 of the connector for continuity
to ground.
(5) Check for tachometer signal from the Power-
train Control Module by connecting an AC DIGITAL
VOLTMETER to Pin J1-7 of the connector and
ground. A reading of at least 1.0 volt should be
present with the engine running.
(a) If the voltage is NOT within specification, go
to Step 6.
(b) If the voltage is within specification, go to
Step 7.
(6) If there is less than 1.0 volt at Pin J1-7 of the
connector, check for continuity between Pin J1-7 and
Pin 73 of the Powertrain Control Module connector
(Fig. 11). Also, check the connector at the Powertrain
Control Module for damaged pins or terminal push
outs.
(7) If the voltage is less than 1.0 volt at Pin J1-7 of
the connector and there is continuity between Pin
J1-7 and Pin 73 of the PCM connector, replace the
Powertrain Control Module.
Fig. 10 Cluster Connector
Fig. 11 Powertrain Control Module Pin Location
PLINSTRUMENT PANEL AND SYSTEMS 8E - 5
DIAGNOSIS AND TESTING (Continued)

(8) If all tests performed test good, replace the dial
and gauge assembly.
(9) If the tachometer continues to be inoperative,
replace the print circuit board.
TEMPERATURE GAUGE
(1) Disconnect the coolant temperature sensor
(Fig. 12).
(2) Turn ignition switch ON. The temperature
gauge should be at its lowest position. Turn ignition
switch OFF.
(3) Ground temperature gauge sending unit con-
nector Pin 3. Refer to Group 8W, wiring Diagrams.
Turn ignition switch ON. The temperature gauge
should be at its highest position. After the seat belt
lamp goes out, the cluster should chime for about
eight seconds.
(a) If OK, check temperature sending unit con-
nector for proper connection. If connections are OK,
replace the sending unit.
(b) If not OK, and the high temperature chime
sounds but the gauge shows cold, replace the gauge
assembly. If gauge is still not working, replace the
printed circuit board.
SPEEDOMETER SYSTEM
The vehicle is equipped with a electronically driven
speedometer and odometer assemblies. A signal is
sent from a transmission-mounted vehicle speed sen-
sor to the speedometer circuitry through the wiring
harness.
SEAT BELT REMINDER SYSTEM TEST
For testing of this system refer to Group 8U,
Chime Warning/Reminder Systems.
SENDING UNIT
When a problem occurs with a cluster gauge check
for a defective sending unit or wiring. Do this before
disassembling the cluster.(1) Sending units and wiring can be checked by
grounding the connector leads at the sending unit in
the vehicle.
(2) With the ignition in the ON position, a
grounded input will cause the fuel or temperature
gauge to read at or above maximum.
SERVICE ENGINE SOON INDICATOR
Refer to Group 25, Emission Control Systems for
procedures.
VEHICLE SPEED SENSOR TEST
To test the vehicle speed sensor and related compo-
nents use a scan tool (DRB), and refer to the appro-
priate Powertrain Diagnostics Test Procedure
Manual.
REMOVAL AND INSTALLATION
ASH RECEIVER RETAINER AND LAMP
REMOVAL
(1) Open up and remove the ash receiver recepta-
cle.
(2) Remove the center bezel.
(3) Remove the two ash receiver retainer attaching
screws from the upper-rearward face and remove
retainer.
(4) For lamp replacement, remove the clamp and
lamp hood from the top of the retainer. Remove the
wiring clip at the forward edge of the retainer and
remove the lamp socket from the hood and replace
lamp.
INSTALLATION
For installation reverse the above procedures.
When installing the retainer ensure that the forward
tabs are inserted properly into the slots in the instru-
ment panel.
CENTER BEZEL
REMOVAL
(1) Open the ash receiver receptacle.
(2) Grasp the bezel and pull rearward disengaging
the clips.
INSTALLATION
For installation, reverse the above procedures.
CIGAR LIGHTER RECEPTACLE
REMOVAL
(1) Remove the cigar lighter element.
(2) Reach underneath the instrument panel
through the bottom access hole and disconnect the
cigar lighter receptacle wiring connectors.
Fig. 12 Engine Coolant Temperature Sensor
8E - 6 INSTRUMENT PANEL AND SYSTEMSPL
DIAGNOSIS AND TESTING (Continued)

HEATER A/C CONTROL BLOWER SWITCH
The switch is not serviced, replace heater A/C con-
trol. Refer to the Heater A/C Control Removal and
Installation.
HEATER A/C CONTROL LAMP
REMOVAL
(1) Remove the Heater A/C Control. Refer to the
Heater A/C Control Removal.
(2) Remove the two center knobs by pulling the
knob rearward.
(3) Replace the lamp.
INSTALLATION
For installation, reverse the above procedures.
HEATER CONTROL BLOWER SWITCH
The switch is not serviced, replace the heater con-
trol. Refer to the A/C Heater Control Removal and
Installation.
IGNITION KEY LAMP
REMOVAL
(1) Remove the steering column cover. Refer to
Steering Column Cover Removal.
(2) Disconnect the lamp hood from the base panel.
(3) Remove the lamp socket from hood and replace
the lamp.
INSTALLATION
For installation, reverse the above procedures.
INSTRUMENT PANEL
REMOVAL
CAUTION: Disconnect battery negative cable, in
engine compartment, before servicing instrument
panel.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the floor console. Refer to Floor Con-
sole Removal.
(3) Remove the right and left cowl side trim pan-
els (Fig. 19).
(4) Remove the steering column cover and liner.
(5) Remove the top cover and cluster bezel assem-
bly.
(6) Remove the right and left trim panel.
(7) Remove the defroster upper duct by lifting it
up.
(8) Remove the center outlet duct by pulling rear-
ward.(9) Disconnect the Heater A/C Control, by remov-
ing the control cables clips with a screwdriver and
remove the wire connector.
CAUTION: Lock the steering wheel in the straight
ahead position. This will prevent clockspring dam-
age when the steering wheel rotates freely.
(10) Disconnect the steering column at the bottom
slap together joint.
(11) Disconnect the ATX shifter interlock cable at
the shifter, if equipped.
(12) Disconnect the instrument panel wiring as
required.
(13) Remove the four attaching screws at the cen-
ter floor pan bracket (Fig. 20).
(14) Remove the four attaching screws at steering
column.
(15) Remove the four cowl top nuts.
(16) Remove the attaching screws from the left
and right lower cowl side bracket (Fig. 21).
(17) Remove the two attaching screws from the left
upper cowl side and one from the right upper cowl
side.
(18) Pull the instrument panel rearward away
from the dash/plenum.
(19) Remove the instrument panel from vehicle.
INSTALLATION
For installation, reverse the above procedures.
LEFT TRIM PANEL
REMOVAL
(1) Remove the top cover and cluster bezel (Fig.
19).
(2) Remove the steering column cover.
(3) Remove the two attaching screws along the
bottom and the one at the top of the trim panel and
pull rearward to remove.
INSTALLATION
For installation, reverse the above procedures.
ODOMETER
REMOVAL
(1) Remove the instrument panel top cover and
cluster bezel.
(2) Remove the four screws attaching cluster to
instrument panel (Fig. 22).
(3) Remove the cluster.
(4) Remove the screws attaching PC board cover to
cluster.
(5) Disconnect the odometer connector from the
printed circuit board.
8E - 10 INSTRUMENT PANEL AND SYSTEMSPL
REMOVAL AND INSTALLATION (Continued)

AUDIO SYSTEM
CONTENTS
page page
GENERAL INFORMATION
INTRODUCTION......................... 1
DESCRIPTION AND OPERATION
INTERFERENCE ELIMINATION.............. 1
DIAGNOSIS AND TESTING
ANTENNA.............................. 3
AUDIO DIAGNOSTIC TEST PROCEDURES..... 1BENCH TEST FOR ANTENNA MALFUNCTION . . 3
REMOVAL AND INSTALLATION
ANTENNA.............................. 3
FRONT DOOR SPEAKER................... 4
INSTRUMENT PANEL SPEAKER............. 4
RADIO................................. 4
REAR SHELF SPEAKER(S)................. 5
GENERAL INFORMATION
INTRODUCTION
Operating instructions for the factory installed
audio systems can be found in the Owner's Manual
provided with the vehicle.
The vehicles are equipped with an Interior (Igni-
tion Off Draw) fuse in the Power Distribution Center
located in the engine compartment. After the Interior
(IOD) fuse or battery has been disconnected the clock
will require resetting.
DESCRIPTION AND OPERATION
INTERFERENCE ELIMINATION
The radio utilizes a ground wire plugged on to a
blade terminal and is bolted to the radio chassis.
Both connector and terminal should be securely
attached. The engine has three separate ground
straps to suppress ignition noise which may interfere
with radio reception.
²Left engine mount clip on strap
²Engine to shock tower reinforcement
²Rear strut to body, clip-on strap
Inductive type spark plug cables in the high ten-
sion circuit of the ignition system complete the inter-
ference suppression. Faulty or deteriorated spark
plug wires should be replaced.
In addition, there is a capacitor mounted on the
cylinder head which also helps suppress ignition
noise.
DIAGNOSIS AND TESTING
AUDIO DIAGNOSTIC TEST PROCEDURES
CAUTION: The CD player will only operate between
approximate temperatures of -23ÉC and +65ÉC (-10ÉF
and +145ÉF).
Whenever a radio malfunction occurs;
(1) First check FUSES:
(a) Power Distribution Center (PDC), Interior
lamp fuse, M1 - Radio Memory Feed
(b) Fuse Block:
(I) Fuse 12, Illumination in the fuse block
(II) Fuse 16, Ignition feed in the fuse block
NOTE: The vehicles are shipped with the INTERIOR
LAMP fuse disconnected.
(2) Verify, the radio wire harness are properly con-
nected before starting normal diagnosis and repair
procedures. Refer to Audio Diagnosis table and/or
Group 8W, Wiring Diagrams, Radio Section.
PLAUDIO SYSTEM 8F - 1

VEHICLE SPEED CONTROL SYSTEM
CONTENTS
page page
GENERAL INFORMATION
INTRODUCTION......................... 1
DESCRIPTION AND OPERATION
POWERTRAIN CONTROL MODULE.......... 3
SERVO CABLE.......................... 3
SPEED CONTROL SERVO.................. 1
SPEED CONTROL SWITCHES.............. 2
STOP LAMP SWITCH..................... 3
VACUUM RESERVOIR.................... 3
VEHICLE SPEED AND DISTANCE............ 3
DIAGNOSIS AND TESTING
CHECKING FOR DIAGNOSTIC CODES........ 4
ELECTRICAL TESTS AT POWERTRAIN
CONTROL MODULE..................... 7
OVERSHOOT/UNDERSHOOT FOLLOWING
SPEED CONTROL SET................... 6ROAD TEST............................ 3
SERVO VACUUM TEST.................... 6
SPEED CONTROL ELECTRICAL TEST........ 4
SPEED CONTROL SWITCH TEST............ 6
STOP LAMP SWITCH TEST................ 6
VACUUM SUPPLY TEST................... 8
VEHICLE SPEED SENSOR................. 8
REMOVAL AND INSTALLATION
POWERTRAIN CONTROL MODULE......... 10
SPEED CONTROL SERVO CABLE............ 9
SPEED CONTROL SERVO.................. 8
SPEED CONTROL SWITCH................. 8
STOP LAMP SWITCH.................... 8
VACUUM RESERVOIR................... 10
VEHICLE SPEED SENSOR................ 10
GENERAL INFORMATION
INTRODUCTION
The speed control system is electronically con-
trolled and vacuum operated. The electronic control
is integrated into the powertrain control module
which is located in the engine compartment. The con-
trols are located on the steering wheel and consist of
five switches. The ON, OFF, and SET buttons are
located on the left side of the airbag module. The
RESUME/ACCEL, CANCEL and COAST buttons are
located on the right side of the airbag module (Fig.
1). For identification and location of the major com-
ponents (Fig. 2) and (Fig. 3).
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 WIND-
ING, ICY, SNOW COVERED, OR SLIPPERY.
DESCRIPTION AND OPERATION
SPEED CONTROL SERVO
The servo unit consists of a solenoid valve body,
and a vacuum chamber. The PCM controls the sole-noid valve body. The solenoid valve body controls the
application and release of vacuum to the diaphragm
of the vacuum servo. The servo unit cannot be
repaired and is serviced only as a complete assembly.
Fig. 1 Speed Control Switch
PLVEHICLE SPEED CONTROL SYSTEM 8H - 1

SPEED CONTROL SWITCHES
There are two separate switch pods that operate
the speed control system. The steering-wheel-
mounted switches use multiplexed circuits to provide
inputs to the PCM for ON, OFF, RESUME, ACCEL-
ERATE, SET, DECEL and CANCEL modes. Refer to
the owner's manual for more information on speed
control switch functions and setting procedures.When speed control is selected by depressing the
ON switch, the PCM allows a set speed to be stored
in RAM for speed control. To store a set speed,
depress the SET switch while the vehicle is moving
at a speed between 30 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:
²Stepping on the brake pedal
²Depressing the OFF switch
²Depressing the CANCEL switch.
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 disengaged for any of the following con-
ditions:
²An indication of Park or Neutral
²An rpm increase without a VSS signal increase
(indicates that the clutch has been disengaged)
²Excessive engine rpm (indicates that the trans-
mission may be in a low gear)
²The VSS signal increases at a rate of 10 mph
per second (indicates that the co-efficient of friction
between the road surface and tires is extremely low)
²The VSS signal decreases at a rate of 10 mph
per second (indicates that the vehicle may have
decelerated at an extremely high rate)
²If the actual speed is not within 20 mph of the
set speed
The previous disengagement conditions are pro-
grammed for added safety.
Once the speed control has been disengaged,
depressing the ACCEL switch when speed is greater
than 25 mph restores the vehicle to the target speed
that was stored in the PCM.
NOTE: Depressing the OFF switch will erase the
set speed stored in the PCM's RAM.
While the speed control is engaged, the driver can
increase the vehicle speed by depressing the ACCEL
switch. The new target speed is stored in the PCM
when the ACCEL is released. The PCM also has a
9tap-up9feature in which vehicle speed increases at a
rate of approximately 2 mph for each momentary
switch activation of the ACCEL switch. The PCM
also provides a means to decelerate without disen-
gaging speed control. To decelerate from an existing
recorded target speed, depress and hold the COAST
switch until the desired speed is reached, then
release the switch.
Fig. 2 MTX Speed Control System
Fig. 3 ATX Speed Control System
8H - 2 VEHICLE SPEED CONTROL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

The individual switches cannot be repaired. If one
switch fails, the entire switch module must be
replaced.
STOP LAMP SWITCH
Vehicles equipped with the speed control option use
a dual function stop lamp switch. The switch is
mounted on the brake pedal mounting bracket under
the instrument panel. The PCM monitors the state of
the dual function stop lamp switch. Refer to Group 5,
Brakes for more information on stop lamp switch ser-
vice and adjustment procedures.
SERVO CABLE
The speed control servo cable is connected between
the speed control vacuum servo diaphragm and the
throttle body control linkage. This cable causes the
throttle control linkage to open or close the throttle
valve in response to movement of the vacuum servo
diaphragm.
POWERTRAIN CONTROL MODULE
The speed control electronic control circuitry is
integrated into the Powertrain Control Module
(PCM). The PCM is located in the engine compart-
ment. The PCM speed control functions are moni-
tored by the On-Board Diagnostics (OBD). All OBD-
sensed systems are monitored by the PCM. Each
monitored circuit is assigned a Diagnostic Trouble
Code (DTC). The PCM will store a DTC in electronic
memory for any failure it detects. See On-Board
Diagnostic Tests in this group for more information.
The PCM cannot be repaired and must be replaced if
faulty.
USE THE DRB SCAN TOOL TO REPROGRAM
THE NEW PCM WITH THE VEHICLES ORIGI-
NAL IDENTIFICATION NUMBER (VIN) AND
THE ORIGINAL VEHICLES MILEAGE. IF THIS
STEP IS NOT DONE A DIAGNOSTIC TROUBLE
CODE (DTC) MAY BE SET.
VACUUM RESERVOIR
The reservoir contains a one-way check valve to
trap engine vacuum in the reservoir. When engine
vacuum drops, as in climbing a grade while driving,
the reservoir supplies the vacuum needed to main-
tain proper speed control operation. The vacuum res-
ervoir cannot be repaired and must be replaced if
faulty.
VEHICLE SPEED AND DISTANCE
The 4 speed automatic Transmission Control Mod-
ule (TCM) supplies the speed input to the PCM. The
PCM determines acceleration rates. The speed con-
trol software in the PCM uses vehicle speed and
acceleration to control to the set speed.Vehicles with a 3 speed automatic or manual trans-
mission have a vehicle speed sensor (VSS) mounted
to an adapter near the transmission output shaft.
The sensor is driven through the adapter by a speed-
ometer pinion gear. The VSS pulse signal is moni-
tored by the PCM to determine vehicle speed and to
maintain speed control set speed. Refer to the appro-
priate Powertrain Diagnostic Procedures manual for
diagnosis and testing of this component. Refer to
group 14, Fuel System for Removal/Installation
DIAGNOSIS AND TESTING
ROAD TEST
Perform a vehicle road test to verify reports of
speed control system malfunction. The road test
should include attention to the speedometer. Speed-
ometer operation should be smooth and without flut-
ter 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 problems should
be corrected before proceeding. Refer to Group 8E,
Instrument Panel and Gauges for speedometer diag-
nosis.
If a road test verifies a surge following a set and
the speedometer operates properly see ªOvershoot/
Undershoot on speed control setº.
If a road test verifies an inoperative system, and
the speedometer operates properly, check for:
²A Diagnostic Trouble Code (DTC). If a DTC
exists, conduct tests per the Powertrain Diagnostic
Procedures service manual.
²A misadjusted brake (stop) lamp switch. This
could also cause an intermittent problem.
²Loose or corroded electrical connections at the
servo. Corrosion should be removed from electrical
terminals and a light coating of Mopar Multipurpose
Grease, or equivalent, applied.
²Leaking vacuum reservoir.
²Loose or leaking vacuum hoses or connections.
²Defective one-way vacuum check valve.
²Secure attachment at both ends of the speed
control servo cable.
²Smooth operation of throttle linkage and throttle
body air valve.
²Conduct electrical test at PCM.
²Failed speed control servo. Do the servo vacuum
test.
CAUTION: When test probing for voltage or conti-
nuity 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.
PLVEHICLE SPEED CONTROL SYSTEM 8H - 3
DESCRIPTION AND OPERATION (Continued)