change key battery DODGE NEON 2000 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)

stroke. One plug is the cylinder under compression,
the other cylinder fires on the exhaust stroke. Coil
number one fires cylinders 1 and 4. Coil number two
fires cylinders 2 and 3. The PCM determines which
of the coils to charge and fire at the correct time.
The Auto Shutdown (ASD) relay provides battery
voltage to the ignition coil. The PCM provides a
ground contact (circuit) for energizing the coil. When
the PCM breaks the contact, the energy in the coil
primary transfers to the secondary causing the
spark. The PCM will de-energize the ASD relay if it
does not receive the crankshaft position sensor and
camshaft position sensor inputs. Refer to Auto Shut-
down (ASD) RelayÐPCM Output in this section for
relay operation.
Base timing is non-adjustable, but is set from the
factory at approximately 10ÉBTDC when the engine
is warm and idling.
There is an adaptive dwell strategy that runs dwell
from 4 to 6 msec when rpm is below 3,000 and bat-
tery voltage is 12-14 volts. During cranking, dwell
can be as much as 200 msec. The adaptive dwell is
driven by the sensed current flow through the injec-
tor drivers. Current flow is limited to 8 amps.
The low resistance of the primary coils can allow
current flow in excess of 15 amps. The PCM has a
current sensing device in the coil output circuit. As
dwell time starts, the PCM allows current to flow.
When the sensing device registers 8 amps, the PCM
begins to regulate current flow to maintain and not
exceed 8 amps through the remainder of the dwell
time. This prevents the PCM from being damaged by
excess current flow.
MALFUNCTION INDICATOR (CHECK ENGINE)
LAMPÐPCM OUTPUT
OPERATION
The PCM supplies the malfunction indicator (check
engine) lamp on/off signal to the instrument panel
through the PCI Bus. The PCI Bus is a communica-
tions port. Various modules use the PCI Bus to
exchange information.
The Check Engine lamp comes on each time the
ignition key is turned ON and stays on for 3 seconds
as a bulb test.
The Malfunction Indicator Lamp (MIL) stays on
continuously, when the PCM has entered a Limp-In
mode or identified a failed emission component. Dur-
ing Limp-in Mode, the PCM attempts to keep the
system operational. The MIL signals the need for
immediate service. In limp-in mode, the PCM com-
pensates for the failure of certain components that
send incorrect signals. The PCM substitutes for the
incorrect signals with inputs from other sensors.
If the PCM detects active engine misfire severe
enough to cause catalyst damage, it flashes the MIL.
At the same time the PCM also sets a Diagnostic
Trouble Code (DTC).
For signals that can trigger the MIL (Check
Engine Lamp) refer to the On-Board Diagnos-
tics section.
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 COAST voltage informs the PCM to
coast down to a new desired speed. The speed control
OFF voltage tells the PCM that the speed control
system has deactivated. Refer to the Speed Control
section for more speed control information.
SCI RECEIVEÐPCM OUTPUT
OPERATION
SCI Receive is the serial data communication
receive circuit for the DRB scan tool. The Powertrain
Fig. 27 Ignition Coil Pack
PLFUEL SYSTEM 14 - 41
DESCRIPTION AND OPERATION (Continued)