1999 DODGE NEON Timing

CRANKSHAFT POSITION SENSORÐPCM INPUT
The PCM determines what cylinder to fire from the
crankshaft position sensor input and the camshaft
position sensor input. The second crankshaft counter-
weight has two sets of four timing reference notches
including a 60 degree signature notch (Fig. 7). From
the crankshaft position sensor input the PCM deter-
mines engine speed and crankshaft angle (position).
The notches generate pulses from high to low in
the crankshaft position sensor output voltage. When
a metal portion of the counterweight aligns with the
crankshaft position sensor, the sensor output voltage
goes low (less than 0.5 volts). When a notch aligns
with the sensor, voltage goes high (5.0 volts). As a
group of notches pass under the sensor, the outputvoltage switches from low (metal) to high (notch)
then back to low.
If available, an oscilloscope can display the square
wave patterns of each voltage pulses. From the width
of the output voltage pulses, the PCM calculates
engine speed. The width of the pulses represent the
amount of time the output voltage stays high before
switching back to low. The period of time the sensor
output voltage stays high before switching back to
low is referred to as pulse width. The faster the
engine is operating, the smaller the pulse width on
the oscilloscope.
By counting the pulses and referencing the pulse
from the 60 degree signature notch, the PCM calcu-
lates crankshaft angle (position). In each group of
timing reference notches, the first notch represents
69 degrees before top dead center (BTDC). The sec-
ond notch represents 49 degrees BTDC. The third
notch represents 29 degrees. The last notch in each
set represents 9 degrees before top dead center
(TDC).
The timing reference notches are machined at 20É
increments. From the voltage pulse width the PCM
tells the difference between the timing reference
notches and the 60 degree signature notch. The 60
degree signature notch produces a longer pulse width
than the smaller timing reference notches. If the
camshaft position sensor input switches from high to
low when the 60 degree signature notch passes under
the crankshaft position sensor, the PCM knows cylin-
der number one is the next cylinder at TDC.
The crankshaft position sensor mounts to the
engine block behind the alternator, just above the oil
filter (Fig. 8).
ENGINE COOLANT TEMPERATURE SENSORÐPCM
INPUT
The combination coolant temperature sensor has
two elements. One element supplies coolant temper-
ature signal to the PCM. The other element supplies
coolant temperature signal to the instrument panel
gauge cluster. The PCM determines engine coolant
temperature from the coolant temperature sensor.
As coolant temperature varies the coolant temper-
ature sensors resistance changes resulting in a differ-
ent input voltage to the PCM and the instrument
panel gauge cluster.
When the engine is cold, the PCM will provide
slightly richer air- fuel mixtures and higher idle
speeds until normal operating temperatures are
reached.
SOHC
The coolant sensor threads into the rear of the cyl-
inder head, next to the camshaft position sensor (Fig.
9). New sensors have sealant applied to the threads.
Fig. 5 Target MagnetÐTypical
Fig. 6 Target Magnet Polarity
14 - 26 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

DOHC
The coolant sensor threads into the intake mani-
fold next to the thermostat housing (Fig. 10). New
sensors have sealant applied to the threads.
FUEL LEVEL SENSORÐPCM INPUT
The fuel level sensor (fuel gauge sending unit)
sends a signal to the PCM to indicate fuel level. The
purpose of this feature is to prevent a false setting of
misfire and fuel system monitor trouble codes if the
fuel level is less than approximately 15 percent of its
rated capacity. It is also used to send a signal for fuel
gauge operation via the CCD bus circuits.
HEATED OXYGEN SENSOR (O2S SENSOR)ÐPCM
INPUT
As vehicles accumulate mileage, the catalytic con-
vertor deteriorates. The deterioration results in a
less efficient catalyst. To monitor catalytic convertor
Fig. 7 Timing Reference Notches
Fig. 8 Crankshaft Position Sensor
Fig. 9 Engine Coolant Temperature SensorÐSOHC
Fig. 10 Engine Coolant Temperature SensorÐDOHC
PLFUEL SYSTEM 14 - 27
DESCRIPTION AND OPERATION (Continued)

As Intake Air temperature varies the Intake Air
Temperature sensors resistance changes resulting in
a different input voltage to the PCM.
The IAT sensor and Manifold Absolute Pressure
(MAP) switch are a combined into a single sensor
that attachs to the intake manifold (Fig. 13) or (Fig.
14).
KNOCK SENSORÐPCM INPUT
The knock sensor threads into the side of the cyl-
inder block in front of the starter (Fig. 15). When the
knock sensor detects a knock in one of the cylinders,
it sends an input signal to the PCM. In response, the
PCM retards ignition timing for all cylinders by a
scheduled amount.
Knock sensors contain a piezoelectric material
which sends an input voltage (signal) to the PCM. As
the intensity of the engine knock vibration increases,
the knock sensor output voltage also increases.
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSORÐPCM INPUT
The PCM supplies 5 volts direct current to the
MAP sensor. The MAP sensor converts intake mani-
fold pressure into voltage. The PCM monitors the
MAP sensor output voltage. As vacuum increases,
MAP sensor voltage decreases proportionately. Also,
as vacuum decreases, MAP sensor voltage increases
proportionately.
At key on, before the engine is started, the PCM
determines atmospheric air pressure from the MAP
sensor voltage. While the engine operates, the PCM
determines intake manifold pressure from the MAP
sensor voltage. Based on MAP sensor voltage and
inputs from other sensors, the PCM adjusts spark
advance and the air/fuel mixture.
The MAP/Intake Air Temperature sensor mounts to
the intake manifold (Fig. 13) and (Fig. 14).
Fig. 12 Downstream Heated Oxygen Sensor
Fig. 13 / MAP/Intake Air Temperature SensorÐSOHC
Fig. 14 MAP/Intake Air Temperature SensorÐDOHC
Fig. 15 Knock Sensor
PLFUEL SYSTEM 14 - 29
DESCRIPTION AND OPERATION (Continued)

POWER STEERING PRESSURE SWITCHÐPCM
INPUT
A pressure sensing switch is located on the power
steering gear. The switch (Fig. 16) provides an input
to the PCM during periods of high pump load and
low engine RPM; such as during parking maneuvers.
When power steering pump pressure exceeds 2758
kPa (400 psi), the switch is open. The PCM increases
idle air flow through the IAC motor to prevent
engine stalling. When pump pressure is low, the
switch is closed.
SENSOR RETURNÐPCM INPUT
The sensor return circuit provides a low electrical
noise ground reference for all of the systems sensors.
The sensor return circuit connects to internal ground
circuits within the powertrain control module.
SPEED CONTROL SERVOSÐPCM OUTPUT
The PCM controls the speed control vacuum servo.
The PCM supplies power, through the brake switch,
to the servo. Based on the speed control switch
inputs to the PCM and the speed control strategy,
the PCM provides ground to the servo vacuum or
vent circuit as required. When the PCM supplies a
ground to the servo vacuum circuit, the speed control
system opens the throttle plate to obtain or maintain
the selected road speed. When the PCM supplies a
ground to the servo vent circuit, the speed control
system releases the throttle plate. Refer to Group 8H
for speed control information.
SCI RECEIVEÐPCM INPUT
SCI Receive is the serial data communication
receive circuit for the DRB scan tool. The Powertrain
Control Module (PCM) receives data from the DRB
through the SCI Receive circuit.
PARK/NEUTRAL POSITION SWITCHÐPCM INPUT
The park/neutral position switch is located on the
automatic transaxle housing (Fig. 17). Manual tran-
saxles do not use park/neutral switches. The switch
provides an input to the PCM to indicate whether
the automatic transaxle is in Park/Neutral, or a drive
gear selection. This input is used to determine idle
speed (varying with gear selection) and ignition tim-
ing advance. The park/neutral input is also used to
cancel vehicle speed control. The park/neutral switch
is sometimes referred to as the neutral safety switch.
THROTTLE POSITION SENSORÐPCM INPUT
The throttle position sensor mounts to the side of
the throttle body (Fig. 18) and (Fig. 19).
The Throttle Position Sensor (TPS) connects to the
throttle blade shaft. The TPS is a variable resistor
that provides the PCM with an input signal (voltage).
The signal represents throttle blade position. As the
position of the throttle blade changes, the resistance
of the TPS changes.
The PCM supplies approximately 5 volts DC to the
TPS. The TPS output voltage (input signal to the
powertrain control module) represents throttle blade
position. The TPS output voltage to the PCM varies
from approximately 0.35 to 1.03 volts at minimum
throttle opening (idle) to a maximum of 3.1 to 4.0
volts at wide open throttle.
Along with inputs from other sensors, the PCM
uses the TPS input to determine current engine oper-
ating conditions. The PCM also adjusts fuel injector
pulse width and ignition timing based on these
inputs.
VEHICLE SPEED SENSORÐPCM INPUT
The vehicle speed sensor is located in the transmis-
sion extension housing (Fig. 20) and (Fig. 21). The
sensor input is used by the PCM to determine vehicle
speed and distance traveled.
Fig. 16 Power Steering Pressure SwitchFig. 17 Park/Neutral Switch
14 - 30 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

disables the A/C compressor clutch for several sec-
onds.
The air conditioning clutch relay is located in the
PDC. The inside top of the PDC cover has a label
showing relay and fuse location.
AUTOMATIC SHUTDOWN RELAYÐPCM OUTPUT
The automatic shutdown (ASD) relay supplies bat-
tery voltage to the fuel injectors, electronic ignition
coil and the heating elements in the oxygen sensors.
A buss bar in the power distribution center (PDC)
supplies voltage to the solenoid side and contact side
of the relay. The ASD relay power circuit contains a
20 amp fuse between the buss bar in the PDC and
the relay. The fuse also protects the power circuit for
the fuel pump relay and pump. The fuse is located in
the PDC. Refer to Group 8W, Wiring Diagrams for
circuit information.
The PCM controls the relay by switching the
ground path for the solenoid side of the relay on and
off. The PCM turns the ground path off when the
ignition switch is in the Off position unless the 02
Heater Monitor test is being run. Refer to Group 25,
On-Board Diagnostics. When the ignition switch is in
the On or Crank position, the PCM monitors the
crankshaft position sensor and camshaft position sen-
sor signals to determine engine speed and ignition
timing (coil dwell). If the PCM does not receive the
crankshaft position sensor and camshaft position sen-
sor signals when the ignition switch is in the Run
position, it will de- energize the ASD relay.
The ASD relay is located in the PDC. The inside
top of the PDC cover has a label showing relay and
fuse location.
CHARGING SYSTEM INDICATOR LAMPÐPCM
OUTPUT
The PCM turns the instrument panel Charging
System Lamp on. Refer to Group 8C for charging sys-
tem information.
FUEL PUMP RELAYÐPCM OUTPUT
The fuel pump relay supplies battery voltage to the
fuel pump. A buss bar in the Power Distribution Cen-
ter (PDC) supplies voltage to the solenoid side and
contact side of the relay. The fuel pump relay power
circuit contains a 20 amp fuse between the buss bar
in the PDC and the relay. The fuse also protects the
power circuit for the Automatic Shutdown (ASD)
relay. The fuse is located in the PDC. Refer to Group
8W, Wiring Diagrams for circuit information.
The PCM controls the fuel pump relay by switch-
ing the ground path for the solenoid side of the relay
on and off. The PCM turns the ground path off when
the ignition switch is in the Off position. When the
ignition switch is in the On position, the PCM ener-gizes the fuel pump. If the crankshaft position sensor
does not detect engine rotation, the PCM de-ener-
gizes the relay after approximately one second.
The fuel pump relay is located in the PDC. The
inside top of the PDC cover has a label showing relay
and fuse location.
DUTY CYCLE EVAP PURGE SOLENOIDÐPCM
OUTPUT
The duty cycle EVAP purge solenoid regulates the
rate of vapor flow from the EVAP canister to the
throttle body. The powertrain control module oper-
ates the solenoid.
During the cold start warm-up period and the hot
start time delay, the PCM does not energize the sole-
noid. When de-energized, no vapors are purged.
The engine enters closed loop operation after it
reaches a specified temperature and the programmed
time delay ends. During closed loop operation, the
PCM energizes and de-energizes the solenoid 5 to 10
times per second, depending upon operating condi-
tions. The PCM varies the vapor flow rate by chang-
ing solenoid pulse width. Pulse width is the amount
of time the solenoid is energized.
The solenoid attaches to a bracket near the front
engine mount (Fig. 22). To operate correctly, the sole-
noid must be installed with the electrical connector
on top.
ELECTRIC EGR TRANSDUCERÐPCM OUTPUT
The Electric EGR Transducer contains an electri-
cally operated solenoid and a back-pressure con-
trolled vacuum transducer (Fig. 23). The PCM
Fig. 22 Duty Cycle EVAP Purge Solenoid
14 - 32 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

(7) Attach the other end of the jumper wire to
relay terminal 86. This activates the relay. The ohm-
meter should now show continuity between relay ter-
minals 87 and 30. The ohmmeter should not show
continuity between relay terminals 87A and 30.
(8) Disconnect jumper wires.
(9) Replace the relay if it did not pass the continu-
ity and resistance tests. If the relay passed the tests,
it operates properly. Check the remainder of the ASD
and fuel pump relay circuits. Refer to group 8W, Wir-
ing Diagrams.
CAMSHAFT AND CRANKSHAFT POSITION SENSOR
Refer to Group 8D, Ignition for Diagnosis and Test-
ing of Camshaft and Crankshaft Sensors.
ENGINE COOLANT TEMPERATURE SENSOR
(1) With the key off, disconnect wire harness con-
nector from coolant temperature sensor (Fig. 79) or
(Fig. 80).(2) Connect a high input impedance (digital) volt-
ohmmeter to terminals A and B (Fig. 81). The ohm-
meter should read as follows:
²Engine/Sensor at normal operating temperature
around 200ÉF should read approximately 700 to
1,000 ohms.
²Engine/Sensor at room temperature around 70ÉF
ohmmeter should read approximately 7,000 to 13,000
ohms.
(3) T
est the resistance of the wire harness between
the PCM 60-way connector terminal 28 and the sensor
harness connector. Also check for continuity between
PCM 60-way connector terminal 51 and the sensor har-
ness connector. Refer to Group 8W, Wiring diagrams for
circuit information. If the resistance is greater than 1
ohm, repair the wire harness as necessary.
HEATED OXYGEN SENSOR
Use an ohmmeter to test the heating element of
the oxygen sensors. Disconnect the electrical connec-
tor from each oxygen sensor. The white wires in the
sensor connector are the power and ground circuits
for the heater. Connect the ohmmeter test leads to
terminals of the white wires in the heated oxygen
sensor connector. Replace the heated oxygen sensor if
the resistance is not between 4 and 7 ohms.
IDLE AIR CONTROL (IAC) MOTOR TEST
To preform a complete test of IAC motor and its
circuitry, refer to DRB scan tool and the appropriate
Powertrain Diagnostics Procedures manual.
KNOCK SENSOR
The engine knock sensor is affected by a number of
factors. A few of these are: ignition timing, cylinder
pressure, fuel octane, etc. The knock sensor generates
an AC voltage whose amplitude increases with the
increase of engine knock. The knock sensor can be
tested with a digital voltmeter. The RMS voltage starts
Fig. 79 Engine Coolant Temperature Sensor
LocationÐSOHC
Fig. 80 Engine Coolant Temperature Sensor
LocationÐDOHC
Fig. 81 Engine Coolant Temperature Sensor
PLFUEL SYSTEM 14 - 47
DIAGNOSIS AND TESTING (Continued)

with an anti-seize compound such as Loctitet771-64 or
equivalent.
INSTALLATION
New sensors have compound on the threads and do
not require an additional coating.
(1) Install sensor using an oxygen sensor crow foot
wrench such as Snap-On tool YA8875 or equivalent
(Fig. 101). Tighten the sensor to 28 N´m (20 ft. lbs.)
torque.
(2) Plug sensor connector.
(3) Lower vehicle.
DOWNSTREAM HEATED OXYGEN SENSOR
The downstream heated oxygen sensor threads into
the exhaust outlet pipe behind the catalytic convertor
(Fig. 102).
REMOVAL
(1) Raise vehicle.
(2) Disconnect electrical connector from sensor.
(3) Disconnect sensor electrical harness from clips
along body.
(4) Remove sensor using an oxygen sensor crow
foot wrench such as Snap-On tool YA8875 or equiva-
lent (Fig. 103).
(5) After removing the sensor, the exhaust mani-
fold threads must be cleaned with an 18 mm X 1.5 +
6E tap. If reusing the original sensor, coat the sensor
threads with an anti-seize compound such as Loctitet
771-64 or equivalent.
INSTALLATION
New sensors have compound on the threads and do
not require an additional coating.
(1) Install sensor using an oxygen sensor crow foot
wrench such as Snap-On tool YA8875 or equivalent
(Fig. 103). Tighten the sensor to 28 N´m (20 ft. lbs.)
torque.(2) Connect sensor electrical harness from clips
along body.
(3) Connect electrical connector from sensor.
(4) Lower vehicle.
AIR CLEANER ELEMENT
Neon vehicles do not use a heated air inlet system.
The PCM adjusts fuel injector pulse width and igni-
tion timing to compensate for different ambient tem-
peratures.
The air cleaner attaches to a bracket on the rear of
the cylinder head. An ambient air duct supplies
underhood air for the engine.
REMOVAL
(1) Remove air intake tube (Fig. 104) from air
cleaner and intake manifold (Fig. 105).
(2) Unfasten clasps on top of air cleaner housing.
Rotate front of housing forward then lift front away
from air cleaner housing (Fig. 106).
Fig. 101 Upstream Heated Oxygen Sensor Removal/
Installation
Fig. 102 Downstream Heated Oxygen Sensor
Fig. 103 Downstream Heated Oxygen Sensor
Removal/Installation
PLFUEL SYSTEM 14 - 55
REMOVAL AND INSTALLATION (Continued)

HEX
CODEGENERIC
SCAN
TOOL
CODEDRB SCAN TOOL
DISPLAYDESCRIPTION OF DIAGNOSTIC TROUBLE CODE
66 P0133 Right Bank Upstream O2S
Slow ResponseOxygen sensor response slower than minimum required
switching frequency.
67 P0135 Right Rear (or just)
Upstream O2S Heater
FailureUpstream oxygen sensor heating element circuit
malfunction.
69 P0141 Right Rear (or just)
Downstream O2S Heater
FailureOxygen sensor heating element circuit malfunction.
6A P0300 Multiple Cylinder Mis-fire Misfire detected in multiple cylinders.
6B P0301 Cylinder #1 Mis-fire Misfire detected in cylinder #1.
6C P0302 Cylinder #2 Mis-fire Misfire detected in cylinder #2.
6D P0303 Cylinder #3 Mis-fire Misfire detected in cylinder #3.
6E P0304 Cylinder #4 Mis-fire Misfire detected in cylinder #4.
70 P0420 Right Rear (or just)
Catalyst Efficency FailureCatalyst efficiency below required level.
71 P0441 Incorrect Pruge Flow Insufficient or excessive vapor flow dtected during
evaporation emission system operation.
72 P1899 P/N Switch Stuck in Park
or in GearIncorrect input state detected for the Park/Neutral
switch, auto. trans. only.
73* P0551 Power Steering Switch
FailurePower steering high pressure seen at high speed (2.5L
only).
76 P0172 Right Rear (or just) Fuel
System RichA rich air/fuel mixture has been indicated by an
abnormally lean correction factor.
77 P0171 Right Rear (or just) Fuel
System LeanA lean air/fuel mixture has been indicated by an
abnormally rich correction factor.
7E P0138 Right Rear (or just)
Downstream O2S Shorted
to VoltageOxygen sensor input voltage maintained above the
normal operating range.
80 P0125 Closed Loop Temp Not
ReachedEngine does not reach 20ÉF within 5 minutes with a
vehicle speed signal.
81 P0140 Right Rear (or just)
Downstream O2S Stays at
CenterNeither reich or lean condition detected from the
downstream oxygen sensor.
84 P0121 TPS Voltage Does Not
Agree With MAPTPS signal does not correlate to MAP sensor.
85 P1390 Timing Belt Skipped 1
tooth or MoreRelationship between Cam and Crank signal is not
correct.
8A P1294 Target Idle Not Reached Actual idle speed does not equal target idle speed.
91 P1299 Vacuum Leak Found (IAC
Fully Seated)MAP sensor signal does not correlate to throttle position
sensor signal. Possible vacuum leak.
92 P1496 5 Volt Supply Output Too
Low5 volt output from regulator does not meet minimum
requirement.
94* P0740 Torq Conv Clu, No RPM
Drop At LockupRelationship between engine speed and vehicle speed
indicates no torque converter clutch engagement (auto.
trans. only).
PLEMISSION CONTROL SYSTEMS 25 - 5
DESCRIPTION AND OPERATION (Continued)