Chrysler neon 1997 Service Manual page 1313

14 - 26 FUEL SYSTEM
DESCRIPTION AND OPERATION (Continued)
• Transmission
gear
switch)
The PCM also adjusts engine idle speed through
the idle air control motor based on the following
inputs.
• Air conditioning sense
• Battery voltage
• Battery temperature
• Brake switch
• Coolant temperature
• Engine speed (crankshaft position sensor)
• Engine run time
• Manifold absolute pressure
• Power steering pressure switch
• Throttle position
• Transmission
gear
switch)
• Vehicle distance (speed)
The Auto Shutdown (ASD) and fuel pump relays
are mounted externally, but turned on and off by the
PCM.
The crankshaft position sensor signal is sent to the
PCM. If the PCM does not receive the signal within
approximately one second of engine cranking, it deac-
tivates the ASD relay and fuel pump relay. When
these relays deactivate, power is shut off from the
fuel injectors, ignition coils, heating element in the
oxygen sensors and the fuel pump.
The PCM contains a voltage converter that
changes battery voltage to a regulated 9 volts direct
current to power the camshaft position sensor, crank-
shaft position sensor and vehicle speed sensor. The
PCM also provides a 5 volt direct current supply for
the manifold absolute pressure sensor and throttle
position sensor.
AIR CONDITIONING PRESSURE TRANSDUCER—
PCM INPUT
The Powertrain Control Module (PCM) monitors
the A/C compressor discharge (high side) pressure
through the air conditioning pressure transducer.
The transducer supplies an input to the PCM. The
PCM engages the A/C compressor clutch if pressure
is sufficient for A/C system operation.
selection (park/neutral
selection (park/neutral
AUTOMATIC SHUTDOWN (ASD) SENSE—PCM
INPUT
The ASD sense circuit informs the PCM when the
ASD relay energizes. A 12 volt signal at this input
indicates to the PCM that the ASD has been acti-
vated. This input is used only to sense that the ASD
relay is energized.
When energized, the ASD relay supplies battery
voltage to the fuel injectors, ignition coils and the
heating element in each oxygen sensor. If the PCM
does not receive 12 volts from this input after
grounding the ASD relay, it sets a Diagnostic Trouble
Code (DTC).
BATTERY VOLTAGE—PCM INPUT
The PCM monitors the battery voltage input to
determine fuel injector pulse width and generator
field control.
If battery voltage is low the PCM will increase
injector pulse width (period of time that the injector
is energized).
BATTERY TEMPERATURE SENSOR—PCM INPUT
The PCM uses the temperature of the battery area
to control the charge rate. The signal is used to reg-
ulate the system voltage. The system voltage is
higher at cold temperatures and is gradually reduced
as temperature is increased.
BRAKE SWITCH—PCM INPUT
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.
PL