1999 DODGE NEON check engine light

NOTE: BLACK OR DARK=0to75%state-of-charge
The battery is INADEQUATELY charged and must
be charged until green dot is visible, (12.4 volts or
greater) before the battery is tested or returned to
use. Refer to Causes of Battery Discharging in this
Group for more information.
NOTE: CLEAR COLOR = Replace Battery
WARNING: DO NOT CHARGE, ASSIST BOOST,
LOAD TEST, OR ADD WATER TO THE BATTERY
WHEN CLEAR COLOR DOT IS VISIBLE. PERSONAL
INJURY MAY OCCUR.
A clear color dot shows electrolyte level in battery
is below the test indicator (Fig. 1). Water cannot be
added to a maintenance free battery. The battery
must be replaced. A low electrolyte level may be
caused by an over charging condition. Refer to Gen-
erator Test Procedures on Vehicle.
CAUSES OF BATTERY DISCHARGING
It is normal to have a small 5 to 25 milliamperes
continuous electrical draw from the battery. This
draw will take place with the ignition in the OFF
position, and the courtesy, dome, storage compart-
ments, and engine compartment lights OFF. The con-
tinuous draw is due to various electronic features or
accessories that require electrical current with the
ignition OFF to function properly. When a vehicle is
not used over an extended period of approximately 20
days the IOD fuse should be pulled. The fuse is
located in the power distribution center. removal of
this fuse will reduce the level of battery discharge.
Refer to the Battery Diagnosis and Testing Table for
proper diagnosis.
ABNORMAL BATTERY DISCHARGING
²Corroded battery posts, cables or terminals.
²Loose or worn generator drive belt.
²Electrical loads that exceed the output of the
charging system due to equipment or accessories
installed after delivery.
²Slow driving speeds in heavy traffic conditions
or prolonged idling with high-amperage electrical
systems in use.
²Defective electrical circuit or component causing
excess Ignition Off Draw (IOD). Refer to Battery
Ignition Off Draw (IOD).
²Defective charging system.
²Defective battery.
BATTERY IGNITION OFF DRAW (IOD)
High current draw on the battery with the ignition
OFF will discharge a battery. After a dead battery is
recharged, the vehicle ignition off draw (IOD) shouldbe checked. To determine if a high current draw con-
dition exists first check the vehicle with a test lamp.
(1) Verify that all electrical accessories are OFF.
²Remove key from ignition switch
²Turn off all lights
²Trunk lid is closed
²Engine compartment hood lamp is disconnected
or lamp removed
²Glove box door is closed
²Sun visor vanity lights are OFF
²All doors are closed
²Allow the ignition key lamp system to time out
in approximately 30 seconds, if equipped.
(2) Disconnect battery negative cable (Fig. 4).
(3) Connect a 12 Volt test lamp, with a cold resis-
tance of 5-7 ohms, between the battery negative cable
clamp and the negative post (Fig. 5). If test lamp
goes out system is OK. If test lamp lights and stays
ON, go to Test Lamp Stays ON procedure.
TEST LAMP STAYS ON
There is either a short circuit or a fault in an elec-
tronic module. Two fuses in the Power Distribution
Center (PDC) feed the modules with ignition off
draw.
²Interior lamps fuse (10 Amp) (IOD) PDC.
²Fuel pump fuse (20 Amp) in PDC
(1) Remove interior lamp and fuel pump fuses. By
removing these fuses all ignition off draw from the
vehicle electronics will be disconnected. The test
lamp should go out. If test lamp goes out go to Step
2. If test lamp does not go out there is a current
draw or short circuit. Refer to Group 8W, Wiring Dia-
grams.
(2) Install the fuel pump fuse. If test lamp lights,
there is a current draw or short circuit in the A14
wiring circuit feed.
(a) Disconnect Powertrain Control Module.
(b) If test lamp goes out, replace Powertrain
Control Module.
(c) If test lamp does not go out, there is a cur-
rent draw or short circuit in the A14 circuit feed.
Refer to Group 8W, Wiring Diagrams.
(3) Install the interior lamp fuse. If test lamp
lights, there is a current draw or short circuit in the
M01 circuit. Refer to Group 8W, Wiring Diagrams. If
test lamp stays out, go to Step 4
(4) Use a multi-meter that has at least a range of
200 milliamperes. Install meter between the battery
negative cable and battery negative post (Fig. 6).
Carefully remove the test lamp without disconnecting
the meter. After all modules time-out the total vehi-
cle IOD should be less than 10 milliamperes. If igni-
tion off draw is more than 10 milliamperes go to Step
5.
(5) Remove both fuses from the Power Distribution
Center:
PLBATTERY 8A - 3
DIAGNOSIS AND TESTING (Continued)

(1) Connect a volt-ampere tester to the battery ter-
minals (Fig. 7). Refer to the operating instructions
provided with the tester being used.
(2) To disable the ignition and fuel systems, dis-
connect the Automatic Shutdown Relay (ASD). The
ASD relay is located in the Power Distribution Cen-
ter (PDC). Refer to the PDC cover for proper relay
location. The 2.5L Diesel Engine, to disable the
engine from starting, disconnect wire connector from
the Fuel Solenoid.
(3) Verify that all lights and accessories are OFF,
and the transmission shift selector is in the PARKposition or with the clutch pedal depressed and SET
parking brake.
CAUTION: Do not overheat the starter motor or
draw the battery voltage below 9.6 volts during
cranking operations.
(4) Rotate and hold the ignition switch in the
START position. Observe the volt-ampere tester (Fig.
6).
²If voltage reads above 9.6 volts, and amperage
draw reads above 280 amps or the Diesel engine
above 450 amps, check for engine seizing or faulty
starter.
²If voltage reads 12.4 volts or greater and amper-
age reads 0 to 10 amps, check for corroded cables
and/or bad connections.
²Voltage below 9.6 volts and amperage draw
above 300 amps or Diesel engine above 500 amps,
the problem is the starter. Replace the starter refer
to starter removal.
(5) After the starting system problems have been
corrected, verify the battery state-of-charge and
Fig. 6 Volt Ampere Tester
Fig. 7 Volt-Ampere Tester Connections
Fig. 4 Test Starter Motor Ground
Fig. 5 Test Battery Positive Cable Resistance
PLSTARTING 8B - 3
DIAGNOSIS AND TESTING (Continued)

performed at each (- ground) connection in this cir-
cuit to locate the excessive resistance.
(7) Testing (+ positive) circuitry:
(a) Touch the positive lead of voltmeter directly
to battery negativePOST.
(b) Touch the negative lead of voltmeter to the
ground terminal stud on the generator case (not
the terminal mounting nut). Voltage should be no
higher than 0.3 volts. If voltage is higher than 0.3
volts, touch test lead to terminal mounting stud
nut and then to the wiring connector. If voltage is
now below 0.3 volts, look for dirty, loose or poor
connection at this point. A voltage drop test may be
performed at each (+ positive) connection in this
circuit to locate the excessive resistance. This test
can also be performed between the generator case
and the engine. If test voltage is higher than 0.3
volts, check for corrosion at generator mounting
points or loose generator mounting.
CURRENT OUTPUT TEST
The current output test will determine if the
charging system can deliver its minimum test cur-
rent (amperage) output. Refer to the Specifications
section at the end of this group for minimum test
current (amperage) requirements.
The first part of this test will determine the com-
bined amperage output of both the generator and the
Electronic Voltage Regulator (EVR) circuitry.
PREPARATION
(1) Determine if any Diagnostic Trouble Codes
(DTC) exist. To determine a DTC, refer to On-Board
Diagnostics in this group. For repair, refer to the
appropriate Powertrain Diagnostic Procedures man-
ual.
(2) Before starting test, make sure battery is in
good condition and is fully-charged. See Group 8A,
Battery for more information.
(3) Check condition of battery cables at battery.
Clean if necessary.
(4) Perform the Voltage Drop Test. This will
ensure clean and tight generator/battery electrical
connections.
(5) Be sure the generator drive belt is properly
tensioned. Refer to Group 7, Cooling System for
information.
(6) A volt/amp tester equipped with both a battery
load control (carbon pile rheostat) and an inductive-
type pickup clamp (ammeter probe) will be used for
this test. Refer to operating instructions supplied
with tester. When using a tester equipped with an
inductive-type clamp, removal of wiring at the gener-
ator will not be necessary.
(7) Start the engine and allow it to reach operating
temperature.
(8) Shut engine off.(9) Turn off all electrical accessories and all vehicle
lighting.
(10) Connect the volt/amp tester leads to the bat-
tery. Be sure the carbon pile rheostat control is in the
OPEN or OFF position before connecting leads. See
Load Test in Group 8A, Battery for more information.
Also refer to the operating instructions supplied with
test equipment.
(11) Connect the inductive clamp (ammeter probe).
Refer to the operating instructions supplied with test
equipment.
(12) If volt/amp tester is not equipped with an
engine tachometer, connect a separate tachometer to
the engine.
TEST
(1) Perform the previous test Preparation.
(2) Fully engage the parking brake.
(3) Start engine.
(4) Bring engine speed to 2500 rpm.
(5) With engine speed held at 2500 rpm, slowly
adjust the rheostat control (load) on the tester to
obtain the highest amperage reading. Do not allow
voltage to drop below 12 volts. Record the reading.
This load test must be performed within 15 sec-
onds to prevent damage to test equipment.On
certain brands of test equipment, this load will be
applied automatically. Refer to the operating manual
supplied with test equipment.
(6) The ammeter reading must meet the Minimum
Test Amps specifications as displayed in the Genera-
tor Ratings chart. This can be found in the Specifica-
tions section at the end of this group. A label stating
a part reference number is attached to the generator
case. On some engines this label may be located on
the bottom of the case. Compare this reference num-
ber to the Generator Ratings chart.
(7) Rotate the load control to the OFF position.
(8) Continue holding engine speed at 2500. If EVR
circuitry is OK, amperage should drop below 15±20
amps. With all electrical accessories and vehicle
lighting off, this could take several minutes of engine
operation. If amperage did not drop, refer to the
appropriate Powertrain Diagnostic Procedures man-
ual for testing.
(9) Remove volt/amp tester.
If minimum amperage could not be met, refer to
the appropriate Powertrain Diagnostic Procedures
manual for testing.
BATTERY TEMPERATURE SENSOR
To perform a complete test of this sensor and its
circuitry, refer to the appropriate Powertrain Diag-
nostic Procedures manual. To test the sensor only,
refer to the following:
(1) The sensor is located under the battery and is
attached to the battery tray (Fig. 5). A two-wire pig-
8C - 8 CHARGING SYSTEMPL
DIAGNOSIS AND TESTING (Continued)

ply circuit shorts to ground, neither sensor will pro-
duce a signal (output voltage to the PCM).
When the ignition key is turned and left in the On
position, the PCM automatically energizes the Auto
Shutdown (ASD) relay. However, the controller de-en-
ergizes the relay within one second because it has
not received a camshaft position sensor signal indi-
cating engine rotation.
During cranking, the ASD relay will not energize
until the PCM receives a camshaft position sensor
signal. Secondly, the ASD relay remains energized
only if the controller senses a crankshaft position
sensor signal immediately after detecting the cam-
shaft position sensor signal.
(1) Check battery voltage. Voltage should approxi-
mately 12.66 volts or higher to perform failure to
start test.
(2) Disconnect the harness connector from the coil
pack (Fig. 20).
(3) Connect a test light to the B+ (battery voltage)
terminal of the coil electrical connector and ground.
The B+ wire for the DIS coil is the center terminal.
Do not spread the terminal with the test light
probe.
(4) Turn the ignition key to theON position.The
test light should flash On and then Off.Do not turn
the Key to off position, leave it in the On posi-
tion.
(a) If the test light flashes momentarily, the
PCM grounded the ASD relay. Proceed to step 5.
(b) If the test light did not flash, the ASD relay
did not energize. The cause is either the relay or
one of the relay circuits. Use the DRB scan tool to
test the ASD relay and circuits. Refer to the appro-
priate Powertrain Diagnostics Procedure Manual.
Refer to the wiring diagrams section for circuit
information.
(5) Crank the engine. (If the key was placed in the
off position after step 4, place the key in the On posi-tion before cranking. Wait for the test light to flash
once, then crank the engine.)
(6) If the test light momentarily flashes during
cranking, the PCM is not receiving a crankshaft posi-
tion sensor signal.
(7) If the test light did not flash during cranking,
unplug the crankshaft position sensor connector.
Turn the ignition key to the off position. Turn the
key to the On position, wait for the test light to
momentarily flash once, then crank the engine. If the
test light momentarily flashes, the crankshaft posi-
tion sensor is shorted and must be replaced. If the
light did not flash, the cause of the no-start is in
either the crankshaft position sensor/camshaft posi-
tion sensor 8 volt supply circuit, or the camshaft
position sensor output or ground circuits.
IGNITION TIMING PROCEDURE
The engines for this vehicle, use a fixed ignition
system. The PCM regulates ignition timing. Basic
ignition timing is not adjustable.
CAMSHAFT POSITION SENSOR AND CRANKSHAFT
POSITION SENSOR
The output voltage of a properly operating cam-
shaft position sensor or crankshaft position sensor
switches from high (5.0 volts) to low (0.3 volts). By
connecting an Moper Diagonostic System (MDS) and
engine analyzer to the vehicle, technicians can view
the square wave pattern.
ENGINE COOLANT TEMPERATURE SENSOR
Refer to Group 14, Fuel System for Diagnosis and
Testing.
INTAKE AIR TEMPERATURE SENSOR
Refer to Group 14, Fuel System, for Diagnosis and
Testing.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
TEST
Refer to Group 14, Fuel System for Diagnosis and
Testing.
THROTTLE POSITION SENSOR
To perform a complete test of the this sensor and
its circuitry, refer to the DRB scan tool and appropri-
ate Powertrain Diagnostics Procedures manual. To
test the throttle position sensor only, refer to the fol-
lowing:
The Throttle Position Sensor (TPS) can be tested
with a digital voltmeter (DVM). The center terminal
of the sensor is the output terminal. One of the other
terminals is a 5 volt supply and the remaining ter-
minal is ground.
Fig. 20 Ignition Coil Engine Harness Connector
PLIGNITION SYSTEM 8D - 9
DIAGNOSIS AND TESTING (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)

(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)

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)