Chrysler neon 1997 Service Manual page 1323

14 - 36 FUEL SYSTEM
DESCRIPTION AND OPERATION (Continued)
IGNITION COIL—PCM OUTPUT
The coil assembly consists of 2 coils molded
together. The coil assembly is mounted over the valve
cover (Fig. 27) or (Fig. 28). High tension leads route
to each cylinder from the coil. The coil fires two
spark plugs every power stroke. One plug is the cyl-
inder 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) Relay—PCM Output in this section for
relay operation.
SPARK INSULATOR PLUG IGNITION COILS
Fig. 27 Ignition Coil Pack—SOHC
Fig. 28 Ignition Coil Pack—DOHC
MALFUNCTION INDICATOR (CHECK ENGINE)
LAMP—PCM OUTPUT
The PCM supplies the malfunction indicator (check
engine) lamp on/off signal to the instrument panel
through the CCD Bus. The CCD Bus is a communi-
cations port. Various modules use the CCD 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 Group 25, On-Board
Dianostics.
The MIL can also display diagnostic trouble codes.
Cycle the ignition switch on, off, on, off, on, within 5
seconds and any diagnostic trouble codes stored in
the PCM will be displayed. Refer to On-Board Diag-
nostics in Group 25, Emission Control Systems Diag-
nostic Trouble Code Descriptions.
RADIATOR FAN CONTROL MODULE—PCM
OUTPUT
The radiator fan runs when coolant temperature
and A/C system pressure demand cooling. The radia-
tor fan circuit contains a Pulse Width Module
(PWM). Refer to the Group 8W for a circuit sche-
matic.
A 5 volt signal is supplied to the PWM. The PCM
provides a pulsed ground for the PWM. Depending
upon the amount of pulse on time, the PWM puts out
a proportional voltage to the fan motor at the lower
speed. For instance, if the on time is 30 percent, then
the voltage to the fan motor will be 3.6 volts.
When engine coolant reaches approximately 99°C
(210°F) the PCM grounds the PWM relay. When the
PCM grounds the relay it operates at a 30% duty
cycle and immediately ramps up to 100% duty cycle.
The PCM de-energizes the PWM relay when coolant
temperature drops to approximately 93°C (199°F).
Also, when the air conditioning pressure switch
closes, the PCM grounds the PWM. The air condi-
tioning switch closes at 285 psi
PL
10 psi. When air