2000 DODGE NEON engine

CLUTCH INTERLOCK/UPSTOP SWITCH
DESCRIPTION
The clutch interlock/upstop switch is an assembly
consisting of two switches: an engine starter inhibit
switch (interlock) and a clutch pedal upstop switch
(Fig. 6). The switch assembly is located in the clutch/
brake pedal bracket assembly (Fig. 7), each switch
being fastened by four plastic wing tabs.
OPERATION
Clutch Interlock Switch
The clutch interlock switch prevents engine starter
operation and inadvertent vehicle movement with the
clutch engaged and the transaxle in gear.
The switch is open while the clutch pedal is at
rest. When the clutch pedal is fully depressed, the
pedal blade contacts and closes the switch, sending a
Fig. 4 Target MagnetÐTypical
1 ± CAM MAGNET/TARGET
2 ± CAMSHAFT POSITION SENSOR
Fig. 5 Target Magnet Polarity
1 ± TARGET MAGNET
Fig. 6 Clutch Interlock/Upstop Switch
1 ± UPSTOP SWITCH
2 ± INTERLOCK SWITCH
3 ± CONNECTOR
Fig. 7 Clutch/Brake Pedal Bracket Assembly
1 ± UPSTOP SWITCH
2 ± CLUTCH PEDAL
3 ± INTERLOCK SWITCH
4 ± CONNECTOR
PLFUEL SYSTEM 14 - 29
DESCRIPTION AND OPERATION (Continued)

signal to the PCM, allowing engine starter operation.
The interlock switch is not adjustable.
Clutch Pedal Upstop Switch
With the clutch pedal at rest, the clutch pedal
upstop switch is closed, allowing speed control oper-
ation. When the clutch pedal is depressed, the upstop
switch opens and signals the PCM to cancel speed
control operation, and enter a modified engine cali-
bration schedule to improve driveability during gear-
to-gear shifts. The upstop switch is not adjustable.
CRANKSHAFT POSITION SENSORÐPCM
INPUT
DESCRIPTION
The crankshaft position sensor mounts to the front
of the engine block (Fig. 8).
OPERATION
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. 9). 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 output
voltage 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 PCM uses the Crankshaft Position sensor to
calculate the following: Engine RPM, TDC number 1
and 4, Ignition coil synchronization, Injection Syn-
chronization, Camshaft-to-crankshaft misalignment
where applicable (Timing belt skipped 1 tooth or
more diagnostic trouble code).
The PCM sends approximately 9 volts to the Hall-
effect sensor. This voltage is required to operate the
Hall-effect chip and the electronics inside the sensor.
A ground for the sensor is provided through the sen-
sor return circuit. The input to the PCM occurs on a
5 volt output reference circuit.
ENGINE COOLANT TEMPERATURE SENSORÐ
PCM INPUT
DESCRIPTION
The coolant sensor threads into the rear of the cyl-
inder head, next to the camshaft position sensor (Fig.
10). New sensors have sealant applied to the threads.
The ECT Sensor is a Negative Thermal Coefficient
(NTC), dual range Sensor. The resistance of the ECT
Sensor changes as coolant temperature changes. This
results in different input voltages to the PCM. The
PCM also uses the ECT Sensor input to operate the
low and high speed radiator cooling fans.
Fig. 8 Crankshaft Position Sensor
14 - 30 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

OPERATION
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.
The PCM has a dual temperature range program
for better sensor accuracy at cold temperatures. At
key-ON the PCM sends a regulated five volt signal
through a 10,000 ohm resistor to the sensor. When
the sensed voltage reaches approximately 1.25 volts
the PCM turns on the transistor. The transistor con-
nects a 1,000 ohm resistor in parallel with the 10,000
ohm resistor. With this drop in resistance the PCM
recognizes an increase in voltage on the input circuit.
FUEL LEVEL SENSORÐPCM INPUT
DESCRIPTION
The fuel gauge level sending unit is attached to the
fuel pump module.
OPERATION
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 PCI bus circuits.
Fig. 9 Timing Reference Notches
1 ± MACHINED NOTCHES
2 ± CRANKSHAFT POSITION SENSOR
Fig. 10 Engine Coolant Temperature SensorÐSOHC
1 ± ENGINE COOLANT TEMPERATURE SENSOR
2 ± CAMSHAFT POSITION SENSOR
PLFUEL SYSTEM 14 - 31
DESCRIPTION AND OPERATION (Continued)

grammed (fixed) values and inputs from other sen-
sors.
DOWNSTREAM OXYGEN SENSOR 1/2
The Downstream O2 Sensor has two functions.
One function is measuring catalyst efficiency. This is
an OBD II requirement. The oxygen content of theexhaust gasses has significantly less fluctuation than
at the inlet if the converter is working properly. The
PCM compares upstream and Downstream O2 Sen-
sor switch rates under specific operating conditions
to determine if the catalyst is functioning properly.
The other function is a downstream fuel control
which was introduced in 1996. The upstream O2 goal
varies within the window of operation of the O2 Sen-
sor. In the past the goal was a preprogrammed fixed
value based upon where it believed the catalyst oper-
ated most efficiently.
While the Upstream O2 Sensor input is used to
maintain the 14.7:1 air/fuel ratio, variations in
engines, exhaust systems and catalytic converters
may cause this ratio to not be the most ideal for a
particular catalyst and engine. To help maintain the
catalyst operating at maximum efficiency, the PCM
will fine tune the air/fuel ratio entering the catalyst
based upon the oxygen content leaving the catalyst.
This is accomplished by modifying the Upstream O2
Sensor voltage goal.
If the exhaust leaving the catalyst has too much
oxygen (lean ) the PCM increases the upstream O2
goal which increases fuel in the mixture causing less
oxygen to be left over. Conversely, if the oxygen con-
tent leaving the catalyst has is too little oxygen (rich)
the PCM decreases the upstream O2 goal down
which removes fuel from the mixture causing more
oxygen to be left over. This function only occurs dur-
ing downstream closed loop mode operation.
Fig. 13 Heated Oxygen Sensor Systems
1 ± CATALYTIC CONVERTER (LEV EMISSION)
2 ± CLOSE-COUPLED CATALYTIC CONVERTER
(ULEV EMISSION)
3 ± UNDER-FLOOR CATALYTIC CONVERTER
(ULEV EMISSION)
4 ± OXYGEN SENSORS5 ± OXYGEN SENSOR
6 ± CATALYTIC CONVERTER
(FEDERAL EMISSION)
7 ± OXYGEN SENSOR
Fig. 14 Types Of O2 Sensors
1 ± BOSCH
2 ± NEW NTK
3 ± NTK
PLFUEL SYSTEM 14 - 33
DESCRIPTION AND OPERATION (Continued)

IGNITION CIRCUIT SENSEÐPCM INPUT
OPERATION
The ignition circuit sense input tells the Power-
train Control Module (PCM) the ignition switch has
energized the ignition circuit.
Battery voltage is also supplied to the PCM
through the Ignition Switch when the ignition is in
the RUN or START position. This is called the9igni-
tion senseº circuit and is used to ªwake upº the PCM.
Voltage on the ignition input can be as low as 6 volts
and the PCM will still function. Voltage is supplied to
this circuit to power the 8-volt regulator and to allow
the PCM to perform fuel, ignition and emissions con-
trol functions. The battery voltage on this line is sup-
plied to the 8-volt regulator which then passes on a
power-up supply to the 5-volt regulator.
INLET AIR TEMPERATURE SENSORÐPCM
INPUT
DESCRIPTION
The IAT sensor attaches to the intake air duct
(Fig. 15).
The IAT Sensor is a Negative Temperature Coeffi-
cient (NTC) Sensor that provides information to the
PCM regarding the temperature of the air entering
the intake manifold.
OPERATION
Intake Air Temperature
The inlet air temperature sensor replaces the
intake air temperature sensor and the battery tem-
perature sensor. The PCM uses the information from
the inlet air temperature sensor to determine valuesto use as an intake air temperature sensor and a bat-
tery temperature sensor.
The Intake Air Temperature (IAT) sensor value is
used by the PCM to determine air density.
The PCM uses this information to calculate:
²Injector pulse width
²Adjustment of ignition timing (to prevent spark
knock at high intake air temperatures)
Battery Temperature
The inlet air temperature sensor replaces the
intake air temperature sensor and the battery tem-
perature sensor. The PCM uses the information from
the inlet air temperature sensor to determine values
for the PCM to use as an intake air temperature sen-
sor and a battery temperature sensor.
The battery temperature information along with
data from monitored line voltage (B+), is used by the
PCM to vary the battery charging rate. System volt-
age will be higher at colder temperatures and is
gradually reduced at warmer temperatures.
The battery temperature information is also used
for OBD II diagnostics. Certain faults and OBD II
monitors are either enabled or disabled depending
upon the battery temperature sensor input (example:
disable purge and EGR, enable LDP). Most OBD II
monitors are disabled below 20ÉF.
KNOCK SENSORÐPCM INPUT
DESCRIPTION
The knock sensor threads into the side of the cyl-
inder block (Fig. 16). The knock sensor is designed to
detect engine vibration that is caused by detonation.
Fig. 15 Inlet Air Temperature Sensor
Fig. 16 Knock Sensor
14 - 34 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

OPERATION
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 cyl-
inders 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.
The voltage signal produced by the knock sensor
increases with the amplitude of vibration. The PCM
receives as an input the knock sensor voltage signal.
If the signal rises above a predetermined level, the
PCM will store that value in memory and retard
ignition timing to reduce engine knock. If the knock
sensor voltage exceeds a preset value, the PCM
retards ignition timing for all cylinders. It is not a
selective cylinder retard.
The PCM ignores knock sensor input during engine
idle conditions. Once the engine speed exceeds a
specified value, knock retard is allowed.
Knock retard uses its own short term and long
term memory program.
Long term memory stores previous detonation
information in its battery-backed RAM. The maxi-
mum authority that long term memory has over tim-
ing retard can be calibrated.
Short term memory is allowed to retard timing up
to a preset amount under all operating conditions (as
long as rpm is above the minimum rpm) except WOT.
The PCM, using short term memory, can respond
quickly to retard timing when engine knock is
detected. Short term memory is lost any time the
ignition key is turned off.
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSORÐPCM INPUT
DESCRIPTION
The MAP sensor mounts to the intake manifold
(Fig. 17).
OPERATION
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 andinputs from other sensors, the PCM adjusts spark
advance and the air/fuel mixture.
If the PCM considers the MAP Sensor information
inaccurate, the PCM moves into ªlimp-inº mode.
When the MAP Sensor is in limp-in, the PCM limits
the engine speed as a function of the Throttle Posi-
tion Sensor (TPS) to between 1500 and 4000 rpm. If
the MAP Sensor sends realistic signals once again,
the PCM moves out of limp-in and resumes using the
MAP values.
During limp-in a DTC is set and the MIL illumi-
nates.
POWER STEERING PRESSURE SWITCHÐPCM
INPUT
DESCRIPTION
A pressure sensing switch is located on the power
steering gear.
OPERATION
The switch (Fig. 18) 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. The PCM sends 12 volts through a
resister to the sensor circuit to ground. When pump
pressure is low, the switch is closed.
SENSOR RETURNÐPCM INPUT
OPERATION
The sensor return circuit provides a low electrical
noise ground reference for all of the systems sensors.
Fig. 17 Manifold Absolute Pressure Sensor
PLFUEL SYSTEM 14 - 35
DESCRIPTION AND OPERATION (Continued)

The sensor return circuit connects to internal ground
circuits within the Powertrain Control Module
(PCM).
SPEED CONTROLÐPCM INPUT
OPERATION
The speed control system provides five separate
voltages (inputs) to the Powertrain Control Module
(PCM). The voltages correspond to the ON, OFF,
SET, RESUME, CANCEL, and COAST.
The speed control ON voltage informs the PCM
that the speed control system has been activated.
The speed control SET voltage informs the PCM that
a fixed vehicle speed has been selected. The speed
control RESUME voltage indicates the previous fixed
speed is requested. The speed control CANCEL volt-
age tells the PCM to deactivate but retain set speed
in memory (same as depressing the brake pedal). The
speed control OFF voltage tells the PCM that the
speed control system has deactivated.
Inputs Required for Operation
The inputs required by the PCM to operate the
Speed Control System include:
²Speed Control switches
²Brake switch
²Park/Neutral switch
²Vehicle speed signal
²Engine speed
²CCD bussed message from TCM
SCI RECEIVEÐPCM INPUT
OPERATION
SCI Receive is the serial data communication
receive circuit for the DRB scan tool. The PowertrainControl Module (PCM) receives data from the DRB
through the SCI Receive circuit.
PARK/NEUTRAL POSITION SWITCHÐPCM
INPUT
DESCRIPTION
The park/neutral position switch is located on the
automatic transaxle housing (Fig. 19).
OPERATION
Manual transaxles 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 timing advance. The park/neutral input
is also used to cancel vehicle speed control. The park/
neutral switch is sometimes referred to as the neu-
tral safety switch.
The PCM delivers 8.5 volts to the center terminal
of the Park/Neutral switch. When the gear shift lever
is moved to either the Park or the Neutral position,
the PCM receives a ground signal from the Park/
Neutral switch. With the shift lever positioned in
Drive or Reverse, the Park/Neutral switch contacts
open, causing the signal to the PCM to go high.
THROTTLE POSITION SENSORÐPCM INPUT
DESCRIPTION
The throttle position sensor mounts to the side of
the throttle body (Fig. 20).
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
Fig. 18 Power Steering Pressure Switch
1 ± POWER STEERING PRESSURE SWITCH
Fig. 19 Park/Neutral Switch
1 ± PARK/NEUTRAL SWITCH
2 ± TRANSAXLE HOUSING
14 - 36 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

position of the throttle blade changes, the resistance
of the TPS changes.
OPERATION
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.
When the TPS indicates a voltage that is too high,
too low or not believable, the PCM sets a DTC. When
the DTC is set, the MIL is illuminated and the PCM
moves into limp-in mode. Limp-in for the TPS is
divided into three categories:
²Idle
²Part-throttle
²Wide open throttle (WOT)
VEHICLE SPEED SIGNAL (VSS)ÐPCM INPUT
DESCRIPTION
The PCM requires the VSS to be able to control
the following programs:
²Speed Control
²IAC motor (during deceleration)
²Injection pulse width (during deceleration)
²OBD II diagnostics
²PCM mileage EEPROM
²Road speed shutdown
²Speedometer/Odometer (bused message)NOTE: Road Speed Shutdown is the PCM shutting
off fuel injectors above a preset vehicle speed.
The vehicle speed sensor is located in the transmis-
sion extension housing (Fig. 21) and (Fig. 22).
OPERATION
The vehicle speed sensor on 3 speed automatic and
manual transaxle vehicles is a Hall-effect sensor.
This sensor is mechanically driven by a pinion gear
that is in mesh with the right axle drive shaft. The
hall-effect sensor switches a 5 volt signal sent from
the PCM from a ground to an open circuit.
Fig. 20 Throttle Position Sensor and Idle Air Control
Motor
Fig. 21 Vehicle Speed SensorÐAutomatic
Transmission
1 ± TRANSAXLE EXTENSION HOUSING
2 ± VEHICLE SPEED SENSOR
Fig. 22 Vehicle Speed SensorÐManual
Transmission
1 ± TRANSAXLE
2 ± SPEED SENSOR
3 ± SPEED SENSOR RETAINING BOLT
PLFUEL SYSTEM 14 - 37
DESCRIPTION AND OPERATION (Continued)