speed DODGE NEON 1999 Service Service Manual

the camshaft position sensor (Fig. 8) or (Fig. 9) and
crankshaft position sensor. From the two inputs, the
PCM determines crankshaft position.
The camshaft position sensor attaches to the rear
of the cylinder head (Fig. 10). A target magnet
attaches to the rear of the camshaft and indexes to
the correct position. The target magnet has four dif-
ferent poles arranged in an asymmetrical pattern. As
the target magnet rotates, the camshaft position sen-
sor senses the change in polarity (Fig. 11). The sen-
sor input switches from high (5 volts) to low (0.30
volts) as the target magnet rotates. When the north
pole of the target magnet passes under the sensor,
the output switches high. The sensor output switches
low when the south pole of the target magnet passes
underneath.
The camshaft position sensor is mounted to the
rear of the cylinder head. The sensor also acts as a
thrust plate to control camshaft endplay on SOHC
engines.
COMBINATION ENGINE COOLANT TEMPERATURE
SENSOR
The coolant temperature sensor provides an input
voltage to the PCM and a separate input voltage to
the temperature gauge on the instrument panel. The
PCM determines engine coolant temperature from
the coolant temperature sensor. As coolant tempera-
ture varies, the coolant temperature sensor resis-
tance changes resulting in a different input voltage
to the PCM.
When the engine is cold, the PCM will demand
slightly richer air-fuel mixtures and higher idle
speeds until normal operating temperatures are
reached.
Fig. 8 Camshaft Position SensorÐSOHC
Fig. 9 Camshaft Position SensorÐDOHC
Fig. 10 Target Magnet ÐTypical
Fig. 11 Target Magnet Polarity
PLIGNITION SYSTEM 8D - 5
DESCRIPTION AND OPERATION (Continued)

Connect the DVM between the center and sensor
ground terminal. Refer to Group 8W - Wiring Dia-
grams for correct pinout.
With the ignition switch in the ON position, check
the output voltage at the center terminal wire of the
connector. Check the output voltage at idle and at
Wide-Open-Throttle (WOT). At idle, TPS output volt-
age should be approximately 0.38 volts to 1.2 volts.
At wide open throttle, TPS output voltage should be
approximately 3.1 volts to 4.4 volts. The output volt-
age should gradually increase as the throttle plate
moves slowly from idle to WOT.
Check for spread terminals at the sensor and PCM
connections before replacing the TPS.
SPARK PLUG CONDITION
NORMAL OPERATING CONDITIONS
The few deposits present will be probably light tan
or slightly gray in color with most grades of commer-
cial gasoline (Fig. 21). There will not be evidence of
electrode burning. Gap growth will not average more
than approximately 0.025 mm (.001 in) per 1600 km
(1000 miles) of operation for non platinum spark
plugs. Non-platnium spark plugs that have normal
wear can usually be cleaned, have the electrodes filed
and regapped, and then reinstalled.
CAUTION: Never attempt to file the electrodes or
use a wire brush for cleaning platinum spark plugs.
This would damage the platinum pads which would
shorten spark plug life.Some fuel refiners in several areas of the United
States have introduced a manganese additive (MMT)
for unleaded fuel. During combustion, fuel with MMT
may coat the entire tip of the spark plug with a rust
colored deposit. The rust color deposits can be misdi-
agnosed as being caused by coolant in the combustion
chamber. Spark plug performance is not affected by
MMT deposits.
COLD FOULING (CARBON FOULING)
Cold fouling is sometimes referred to as carbon
fouling because the deposits that cause cold fouling
are basically carbon (Fig. 21). A dry, black deposit on
one or two plugs in a set may be caused by sticking
valves or misfire conditions. Cold (carbon) fouling of
the entire set may be caused by a clogged air cleaner.
Cold fouling is normal after short operating peri-
ods. The spark plugs do not reach a high enough
operating temperature during short operating peri-
ods.Replace carbon fouled plugs with new
spark plugs.
FUEL FOULING
A spark plug that is coated with excessive wet fuel
is called fuel fouled. This condition is normally
observed during hard start periods.Clean fuel
fouled spark plugs with compressed air and
reinstall them in the engine.
OIL FOULING
A spark plug that is coated with excessive wet oil
is oil fouled. In older engines, wet fouling can be
caused by worn rings or excessive cylinder wear.
Break-in fouling of new engines may occur before
normal oil control is achieved.Replace oil fouled
spark plugs with new ones.
OIL OR ASH ENCRUSTED
If one or more plugs are oil or ash encrusted, eval-
uate the engine for the cause of oil entering the com-
bustion chambers (Fig. 22). Sometimes fuel additives
can cause ash encrustation on an entire set of spark
plugs.Ash encrusted spark plugs can be cleaned
and reused.
HIGH SPEED MISS
When replacing spark plugs because of a high
speed miss condition;wide open throttle opera-
tion should be avoided for approximately 80 km
(50 miles) after installation of new plugs.This
will allow deposit shifting in the combustion chamber
to take place gradually and avoid plug destroying
splash fouling shortly after the plug change.
Fig. 21 Normal Operation and Cold (Carbon) Fouling
8D - 10 IGNITION SYSTEMPL
DIAGNOSIS AND TESTING (Continued)

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)

(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)

(2) Lift up the top cover and cluster bezel until the
clips disengage and separate to provide clearance
(Fig. 25).
(3) Rotate the ignition key cylinder to run/on posi-
tion. Insert a screw driver into the access hole at the
bottom of lower shroud to release the ignition key
cylinder.
(4) Pull out the ignition key cylinder.
(5) Remove the three lower to upper shroud
attaching screws through the bottom of the lower
shroud.
(6) Separate the upper and lower shrouds.
INSTALLATION
For installation, reverse the above procedures.
TOP COVER AND CLUSTER BEZEL REMOVAL
REMOVAL
(1) Use care not to scratch the panel. Lift up on
the bottom outer areas of the cluster bezel and alongthe rearward edge of the top cover to disengage the
clips (Fig. 24).
(2) Pull the top cover and cluster bezel rearward
until the forward pins disengage from the instrument
panel.
INSTALLATION
For installation, reverse the above procedures,
making sure that the forward pins engage the index
holes in the instrument panel. Position spring clips
in instrument panel and push firmly until seated.
TRANSMISSION RANGE INDICATOR LAMP
REMOVAL
(1) Raise the floor console (Fig. 16).
(2) Remove the attaching screw from each of the
two forward cup holders of the floor console. Remove
the screws at the rear of the console or inside of the
armrest console bin.
(3) Pull the parking brake lever all the way up.
(4) Lift the floor console at the rear high enough to
gain access to the lamp and socket.
(5) Remove the indicator lamp socket from bezel to
replace the lamp.
INSTALLATION
For installation, reverse the above procedures.
TRUNK LAMP/LENS
REMOVAL
The trunk lamp snaps into the rear shelf panel
reinforcement under/below the package shelf.
(1) Remove the socket assembly by reaching up
above the sheet metal. Push the snap inward and
downward and remove the assembly.
(2) Remove the lamp from socket and pull the
socket from the lens. Replace as necessary.
INSTALLATION
For installation, reverse the above procedures.
VEHICLE SPEED SENSOR
For Vehicle Soeed Sensor Removal and Installa-
tion, refer to Group 14±Fuel Systems for service
procedures.
Fig. 25 Upper/Lower Shroud
8E - 14 INSTRUMENT PANEL AND SYSTEMSPL
REMOVAL AND INSTALLATION (Continued)

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)