2000 DODGE NEON Service Repair Manual

BATTERY VOLTAGEÐPCM INPUT
OPERATION
In order for the PCM to operate, it must be sup-
plied with battery voltage and ground. The PCM
monitors the direct battery feed input to determine
battery charging rate and to control the injector ini-
tial opening point. It also has back-up RAM memory
used to store Diagnostic Trouble Codes (supply work-
ing DTCs). Direct battery feed is also used to perform
key-OFF diagnostics and to supply working voltage
to the controller for OBDII.
The five and eight volt regulators are protected
from shorts to ground. This protection allows diag-
nostics to be performed should the five volt power
supply become shorted to ground at any of the sen-
sors. A short to ground in the five volt power supply
will cause a ªno-startº situation. There is a Diagnos-
tic Trouble Code (DTC) if the five-volt power supply
becomes shorted to ground. Refer to the Diagnostic
Procedures Manual for more details on any on-board
diagnostic information.
If battery voltage is low the PCM will increase
injector pulse width (period of time that the injector
is energized).
The direct battery feed to the PCM is used as a
reference point to sense battery voltage.
Effect on Fuel Injectors
Fuel injectors are rated for operation at a specific
voltage. If the voltage increases, the plunger will
open faster and further (more efficient) and con-
versely, if voltage is low the injector will be slow to
open and will not open as far. Therefore, if sensed
battery voltage drops, the PCM increases injector
pulse-width to maintain the same volume of fuel
through the injector.
Charging
The PCM uses sensed battery voltage to verify that
target charging voltage (determined by Battery Tem-
perature Sensor) is being reached. To maintain the
target charging voltage, the PCM will full field the
generator to 0.5 volt above target then turn OFF to
0.5 volt below target. This will continue to occur up
to a 100 Hz frequency, 100 times per second.
BRAKE SWITCHÐPCM INPUT
OPERATION
When the brake switch is activated, the PCM
receives an input indicating that the brakes are
being applied. The brake switch is mounted on the
brake pedal support bracket.
CAMSHAFT POSITION SENSORÐPCM INPUT
DESCRIPTION
The camshaft position sensor attaches to the rear
of the cylinder head. The PCM determines fuel injec-
tion synchronization and cylinder identification from
inputs provided by the camshaft position sensor (Fig.
3) and crankshaft position sensor. From the two
inputs, the PCM determines crankshaft position.
OPERATION
The PCM sends approximately 8 volts to the hall
affect 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.
A target magnet attaches to the rear of the cam-
shaft and indexes to the correct position. The target
magnet has four different poles arranged in an asym-
metrical pattern (Fig. 4). As the target magnet
rotates, the camshaft position sensor senses the
change in polarity (Fig. 5). The sensor output switch
switches from high (5.0 volts) to low (0.5 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 under-
neath.
The sensor also acts as a thrust plate to control
camshaft endplay.
Fig. 3 Camshaft Position SensorÐSOHC
14 - 28 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

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)

HEATED OXYGEN SENSOR (O2 SENSOR)Ð
PCM INPUT
DESCRIPTION
The upstream oxygen sensor threads into the out-
let flange of the exhaust manifold (Fig. 11).
The downstream heated oxygen sensor threads into
the system depending on emission package (Fig. 12).
Federal package the O2s is mounted after the cata-
lytic convertor, LEV package the O2s is mounted mid
catalytic convertor, ULEV package is mounted
between the catalytic convertor (Fig. 13).
OPERATION
The O2 sensors produce voltages from 0 to 1 volt,
depending upon the oxygen content of the exhaust
gas in the exhaust manifold (Fig. 14). When a large
amount of oxygen is present (caused by a lean air/
fuel mixture), the sensors produce a voltage below
450 mv. When there is a lesser amount present (rich
air/fuel mixture) it produces a voltage above 450 mv.
By monitoring the oxygen content and converting it
to electrical voltage, the sensors act as a rich- lean
switch.
The oxygen sensors are equipped with a heating
element that keeps the sensors at proper operating
temperature during all operating modes. Maintaining
correct sensor temperature at all times allows the
system to enter into closed loop operation sooner.
Also, it allows the system to remain in closed loop
operation during periods of extended idle.
In Closed Loop operation the PCM monitors the O2
sensor input (along with other inputs) and adjusts
the injector pulse width accordingly. During Open
Loop operation the PCM ignores the O2 sensor input.
The PCM adjusts injector pulse width based on pre-
programmed (fixed) values and inputs from other
sensors.
The Automatic Shutdown (ASD) relay supplies bat-
tery voltage to both the upstream and downstream
heated oxygen sensors. The oxygen sensors are
equipped with a heating element. The heating ele-
ments reduce the time required for the sensors to
reach operating temperature.
UPSTREAM OXYGEN SENSOR 1/1
The input from the upstream heated oxygen sensor
tells the PCM the oxygen content of the exhaust gas.
Based on this input, the PCM fine tunes the air-fuel
ratio by adjusting injector pulse width.
The sensor input switches from 0 to 1 volt, depend-
ing upon the oxygen content of the exhaust gas in
the exhaust manifold. When a large amount of oxy-
gen is present (caused by a lean air-fuel mixture), the
sensor produces voltage as low as 0.1 volt. When
there is a lesser amount of oxygen present (rich air-
fuel mixture) the sensor produces a voltage as high
as 1.0 volt. By monitoring the oxygen content and
converting it to electrical voltage, the sensor acts as
a rich-lean switch.
The heating element in the sensor provides heat to
the sensor ceramic element. Heating the sensor
allows the system to enter into closed loop operation
sooner. Also, it allows the system to remain in closed
loop operation during periods of extended idle.
In Closed Loop, the PCM adjusts injector pulse
width based on the upstream heated oxygen sensor
input along with other inputs. In Open Loop, the
PCM adjusts injector pulse width based on prepro-
Fig. 11 Upstream Heated Oxygen Sensor 1/1
1 ± OXYGEN SENSORS
2 ± EXHAUST MANIFOLD
Fig. 12 Downstream Heated Oxygen Sensor 1/2
14 - 32 FUEL SYSTEMPL
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)