DODGE NEON 1999 Service Repair Manual

POWER STEERING PRESSURE SWITCHÐPCM
INPUT
A pressure sensing switch is located on the power
steering gear. The switch (Fig. 16) 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. When pump pressure is low, the
switch is closed.
SENSOR RETURNÐPCM INPUT
The sensor return circuit provides a low electrical
noise ground reference for all of the systems sensors.
The sensor return circuit connects to internal ground
circuits within the powertrain control module.
SPEED CONTROL SERVOSÐPCM OUTPUT
The PCM controls the speed control vacuum servo.
The PCM supplies power, through the brake switch,
to the servo. Based on the speed control switch
inputs to the PCM and the speed control strategy,
the PCM provides ground to the servo vacuum or
vent circuit as required. When the PCM supplies a
ground to the servo vacuum circuit, the speed control
system opens the throttle plate to obtain or maintain
the selected road speed. When the PCM supplies a
ground to the servo vent circuit, the speed control
system releases the throttle plate. Refer to Group 8H
for speed control information.
SCI RECEIVEÐPCM INPUT
SCI Receive is the serial data communication
receive circuit for the DRB scan tool. The Powertrain
Control Module (PCM) receives data from the DRB
through the SCI Receive circuit.
PARK/NEUTRAL POSITION SWITCHÐPCM INPUT
The park/neutral position switch is located on the
automatic transaxle housing (Fig. 17). Manual tran-
saxles 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 tim-
ing advance. The park/neutral input is also used to
cancel vehicle speed control. The park/neutral switch
is sometimes referred to as the neutral safety switch.
THROTTLE POSITION SENSORÐPCM INPUT
The throttle position sensor mounts to the side of
the throttle body (Fig. 18) and (Fig. 19).
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
position of the throttle blade changes, the resistance
of the TPS changes.
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.
VEHICLE SPEED SENSORÐPCM INPUT
The vehicle speed sensor is located in the transmis-
sion extension housing (Fig. 20) and (Fig. 21). The
sensor input is used by the PCM to determine vehicle
speed and distance traveled.
Fig. 16 Power Steering Pressure SwitchFig. 17 Park/Neutral Switch
14 - 30 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

The vehicle speed sensor generates 8 pulses per
sensor revolution. These signals, in conjunction with
a closed throttle signal from the throttle position sen-
sor, indicate a closed throttle deceleration to the
PCM. Under deceleration conditions, the PCM
adjusts the Idle Air Control (IAC) motor to maintain
a desired MAP value.
When the vehicle is stopped at idle, a closed throt-
tle signal is received by the PCM (but a speed sensor
signal is not received). Under idle conditions, the
PCM adjusts the IAC motor to maintain a desired
engine speed.
The vehicle speed sensor signal is also used to
operate the following functions or systems:
²Speedometer
²Speed control²Daytime Running Lights (Canadian Vehicles
only).AIR CONDITIONING CLUTCH RELAYÐPCM
OUTPUT
The PCM controls the air conditioning clutch relay
ground circuit. The A/C clutch relay coil side contains
a 10 amp fuse between the buss bar in the Power
Distribution Center (PDC) and the relay. The power
side of this relay is fused with a 40 amp fuse. When
the PCM receives an air conditioning input, it
grounds the A/C compressor clutch relay and the
radiator fan relay.
When the PCM senses low idle speeds or wide open
throttle through the throttle position sensor, it
removes the ground for the A/C compressor clutch
relay. When the relay de-energizes, the contacts open
preventing air conditioning clutch engagement. Also,
if the PCM senses a part throttle launch condition, it
Fig. 18 Throttle Position Sensor and Idle Air Control
MotorÐSOHC
Fig. 19 Throttle Position Sensor and Idle Air Control
MotorÐDOHC
Fig. 20 Vehicle Speed SensorÐAutomatic
Transmission
Fig. 21 Vehicle Speed SensorÐManual
Transmission
PLFUEL SYSTEM 14 - 31
DESCRIPTION AND OPERATION (Continued)

disables the A/C compressor clutch for several sec-
onds.
The air conditioning clutch relay is located in the
PDC. The inside top of the PDC cover has a label
showing relay and fuse location.
AUTOMATIC SHUTDOWN RELAYÐPCM OUTPUT
The automatic shutdown (ASD) relay supplies bat-
tery voltage to the fuel injectors, electronic ignition
coil and the heating elements in the oxygen sensors.
A buss bar in the power distribution center (PDC)
supplies voltage to the solenoid side and contact side
of the relay. The ASD relay power circuit contains a
20 amp fuse between the buss bar in the PDC and
the relay. The fuse also protects the power circuit for
the fuel pump relay and pump. The fuse is located in
the PDC. Refer to Group 8W, Wiring Diagrams for
circuit information.
The PCM controls the relay by switching the
ground path for the solenoid side of the relay on and
off. The PCM turns the ground path off when the
ignition switch is in the Off position unless the 02
Heater Monitor test is being run. Refer to Group 25,
On-Board Diagnostics. When the ignition switch is in
the On or Crank position, the PCM monitors the
crankshaft position sensor and camshaft position sen-
sor signals to determine engine speed and ignition
timing (coil dwell). If the PCM does not receive the
crankshaft position sensor and camshaft position sen-
sor signals when the ignition switch is in the Run
position, it will de- energize the ASD relay.
The ASD relay is located in the PDC. The inside
top of the PDC cover has a label showing relay and
fuse location.
CHARGING SYSTEM INDICATOR LAMPÐPCM
OUTPUT
The PCM turns the instrument panel Charging
System Lamp on. Refer to Group 8C for charging sys-
tem information.
FUEL PUMP RELAYÐPCM OUTPUT
The fuel pump relay supplies battery voltage to the
fuel pump. A buss bar in the Power Distribution Cen-
ter (PDC) supplies voltage to the solenoid side and
contact side of the relay. The fuel pump relay power
circuit contains a 20 amp fuse between the buss bar
in the PDC and the relay. The fuse also protects the
power circuit for the Automatic Shutdown (ASD)
relay. The fuse is located in the PDC. Refer to Group
8W, Wiring Diagrams for circuit information.
The PCM controls the fuel pump relay by switch-
ing the ground path for the solenoid side of the relay
on and off. The PCM turns the ground path off when
the ignition switch is in the Off position. When the
ignition switch is in the On position, the PCM ener-gizes the fuel pump. If the crankshaft position sensor
does not detect engine rotation, the PCM de-ener-
gizes the relay after approximately one second.
The fuel pump relay is located in the PDC. The
inside top of the PDC cover has a label showing relay
and fuse location.
DUTY CYCLE EVAP PURGE SOLENOIDÐPCM
OUTPUT
The duty cycle EVAP purge solenoid regulates the
rate of vapor flow from the EVAP canister to the
throttle body. The powertrain control module oper-
ates the solenoid.
During the cold start warm-up period and the hot
start time delay, the PCM does not energize the sole-
noid. When de-energized, no vapors are purged.
The engine enters closed loop operation after it
reaches a specified temperature and the programmed
time delay ends. During closed loop operation, the
PCM energizes and de-energizes the solenoid 5 to 10
times per second, depending upon operating condi-
tions. The PCM varies the vapor flow rate by chang-
ing solenoid pulse width. Pulse width is the amount
of time the solenoid is energized.
The solenoid attaches to a bracket near the front
engine mount (Fig. 22). To operate correctly, the sole-
noid must be installed with the electrical connector
on top.
ELECTRIC EGR TRANSDUCERÐPCM OUTPUT
The Electric EGR Transducer contains an electri-
cally operated solenoid and a back-pressure con-
trolled vacuum transducer (Fig. 23). The PCM
Fig. 22 Duty Cycle EVAP Purge Solenoid
14 - 32 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

operates the solenoid based on inputs from the multi-
port fuel injection system. The transducer and EGR
valve are serviced as an assembly.
When the PCM energizes the solenoid, vacuum
does not reach the transducer. Vacuum flows to the
transducer when the PCM de-energizes the solenoid.
When exhaust system back-pressure becomes high
enough, it fully closes a bleed valve in the vacuum
transducer. When the PCM de-energizes the solenoid
and back-pressure closes the transducer bleed valve,
vacuum flows through the transducer to operate the
EGR valve.
De-energizing the solenoid, but not fully closing the
transducer bleed hole (because of low back-pressure),
varies the strength of the vacuum signal applied to
the EGR valve. Varying the strength of the vacuum
signal changes the amount of EGR supplied to the
engine. This provides the correct amount of exhaust
gas recirculation for different operating conditions.
The transducer mounts to the clean air hose and
the EGR valve mount to the rear of the cylinder head
(Fig. 23).
GENERATOR FIELDÐPCM OUTPUT
The PCM regulates the charging system voltage
within a range of 12.9 to 15.0 volts. Refer to Group
8A for Battery system information and 8C for charg-
ing system information.
IDLE AIR CONTROL MOTORÐPCM OUTPUT
The Idle Air Control (IAC) motor is mounted on the
throttle body. The PCM operates the idle air control
motor (Fig. 24). The PCM adjusts engine idle speed
through the idle air control motor to compensate for
engine load, coolant temperature or barometric pres-
sure changes.
The throttle body has an air bypass passage that
provides air for the engine during closed throttle idle.The idle air control motor pintle protrudes into the
air bypass passage and regulates air flow through it.
The PCM adjusts engine idle speed by moving the
IAC motor pintle in and out of the bypass passage.
The adjustments are based on inputs the PCM
receives. The inputs are from the throttle position
sensor, crankshaft position sensor, coolant tempera-
ture sensor, MAP sensor, vehicle speed sensor and
various switch operations (brake, park/neutral, air
conditioning).
DATA LINK CONNECTOR
The data link connector (diagnostic connector)
links the DRB scan tool with the powertrain control
module (PCM). Refer to On-Board Diagnostics in the
General Diagnosis section of this group. The data
link connector is located inside the vehicle, under the
instrument panel, left of the steering column (Fig.
25).
Fig. 23 Electric EGR Backpressure TransducerÐ
Typical
Fig. 24 Idle Air Control Motor Air Bypass PassageÐ
Typical
Fig. 25 Data Link Connector
PLFUEL SYSTEM 14 - 33
DESCRIPTION AND OPERATION (Continued)

FUEL INJECTORSÐPCM OUTPUT
The 2.0L engine uses electrically operated top feed
fuel injectors (Fig. 26). The Automatic Shutdown
(ASD) relay supplies battery voltage to the fuel injec-
tors. The PCM controls the ground path for each
injector in sequence. By switching the ground paths
on and off, the PCM fine-tunes injector pulse width.
Injector pulse width refers to the amount of time an
injector operates.
The PCM determines injector synchronization from
the camshaft position sensor and crankshaft position
sensor inputs. The PCM grounds the ASD and fuel
pump relays after receiving the camshaft position
sensor and crankshaft position sensor inputs.
The PCM energizes the injectors in a sequential
order during all engine operating conditions except
start-up. For the first injector pulse width during
start-up, all injectors are energized at the same time.
Once the PCM determines crankshaft position, it
begins energizing the injectors in sequence.
IGNITION COILÐPCM 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 andcamshaft position sensor inputs. Refer to Auto Shut-
down (ASD) RelayÐPCM Output in this section for
relay operation.
MALFUNCTION INDICATOR (CHECK ENGINE)
LAMPÐPCM 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
Fig. 26 Fuel Injector
Fig. 27 Ignition Coil PackÐSOHC
Fig. 28 Ignition Coil PackÐDOHC
14 - 34 FUEL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

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.
SOLID STATE FAN RELAYÐPCM OUTPUT
The radiator fan runs when coolant temperature
and A/C system pressure demand cooling. The radia-
tor fan circuit contains a Solid State Fan Relay
(SSFR). Refer to the Group 8W for a circuit sche-
matic.
A 5 volt signal is supplied to the SSFR. The PCM
provides a pulsed ground for the SSFR. Depending
upon the amount of pulse on time, the SSFR 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 99ÉC
(210ÉF) the PCM grounds the SSFR 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 SSFR relay when coolant
temperature drops to approximately 93ÉC (199ÉF).
Also, when the air conditioning pressure switch
closes, the PCM grounds the SSFR. The air condi-
tioning switch closes at 285 psi610 psi. When air
conditioning pressure drops approximately 40 psi, the
pressure switch opens and the fan turns off.
The SSFR relay is located on the left front inner
frame just behind the radiator.
SPEED CONTROLÐPCM INPUT
The speed control system provides five separate
voltages (inputs) to the Powertrain Control Module
(PCM). The voltages correspond to the ON/OFF, SET,
RESUME and CANCEL.
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. Refer to Group
8H for more speed control information.
SCI RECEIVEÐPCM OUTPUT
SCI Receive is the serial data communication
receive circuit for the DRB scan tool. The Powertrain
Control Module (PCM) receives data from the DRB
through the SCI Receive circuit.
TACHOMETERÐPCM OUTPUT
The PCM operates the tachometer on the instru-
ment panel. The PCM calculates engine RPM from
the crankshaft position sensor input.
TORQUE CONVERTOR CLUTCH SOLENOIDÐPCM
OUTPUT
Three-speed automatic transaxles use a torque con-
verter clutch solenoid. The PCM controls the engage-
ment of the torque converter clutch through the
solenoid (Fig. 29). The torque converter clutch is
engaged up only in direct drive mode. Refer to Group
21 for transmission information.
DIAGNOSIS AND TESTING
VISUAL INSPECTIONÐSOHC
Before diagnosing or servicing the fuel injection
system, perform a visual inspection for loose, discon-
nected, or misrouted wires and hoses (Fig. 30). A
thorough visual inspection that includes the following
checks saves unnecessary test and diagnostic time.
(1) Inspect the battery connections. Clean corroded
terminals (Fig. 31).
(2) Check the 2 PCM 40-way connector for
stretched wires on pushed out terminals (Fig. 31).
Fig. 29 Torque Convertor Clutch Solenoid
PLFUEL SYSTEM 14 - 35
DESCRIPTION AND OPERATION (Continued)

(3) Open the Power Distribution Center (PDC).
Check for blown fuses. Ensure the relays and fuses
are fully seated in the PDC (Fig. 32). A label on the
underside of the PDC cover shows the locations of
each relay and fuse.
(4) Verify the throttle cable operates freely (Fig.
33).
(5) Check the electrical connections at the idle air
control motor and throttle position sensor (Fig. 34).
(6) Check hose connections between the PCV
valve, vacuum port - intake manifold and the oil sep-
arator (Fig. 35).
(7) Inspect the electrical connections at the MAP
sensor/intake air temperature sensor and the (Fig.
36).
(8) Inspect the fuel injector electrical connections
(Fig. 37).
(9) Inspect the ignition coil electrical connector.
Ensure the spark plug insulators are firmly seated
over the spark plugs (Fig. 38).
Fig. 30 2.0L SOHC Engine Compartment
Fig. 31 Battery, PCM, and PDC
Fig. 32 Power Distribution Center
Fig. 33 Throttle CableÐAutomatic Transmission
Fig. 34 Idle Air Control Motor and Throttle Position
SensorÐTypical
14 - 36 FUEL SYSTEMPL
DIAGNOSIS AND TESTING (Continued)

(10) Inspect the electrical and hose connections at
the duty cycle purge solenoid (Fig. 39).(11) Check the electrical connection to the radiator
fan.
(12) Inspect for corrosion on the electrical connec-
tions at the starter motor solenoid. Check the ground
cable connection below the starter motor (Fig. 40).
(13) Inspect the air cleaner filter element. Replace
as necessary. Check the air induction system for
restrictions.
Fig. 35 PCV Valve
Fig. 36 MAP/Intake Air Temperature Sensor
Fig. 37 Fuel Injectors
Fig. 38 Ignition Coil and Spark PlugsÐTypical
PLFUEL SYSTEM 14 - 37
DIAGNOSIS AND TESTING (Continued)

(14) Check the electrical connection at the knock
sensor (Fig. 41).
(15) Check the electrical connections at the cam-
shaft position sensor and engine coolant temperature
sensor (Fig. 42).
(16) Check the electrical connector at the Elec-
tronic EGR Transducer. Inspect the vacuum and back
pressure hoses at the solenoid and transducer for
leaks (Fig. 43).
(17) Inspect the electrical connections at the gen-
erator (Fig. 44). Check the generator belt for glazing
or damage.
Fig. 39 Duty Cycle Purge Solenoid
Fig. 40 Starter Motor and Ground Strap
Fig. 41 Knock Sensor
Fig. 42 Camshaft Position Sensor and Engine
Coolant Temperature Sensor
Fig. 43 Electronic EGR Transducer
14 - 38 FUEL SYSTEMPL
DIAGNOSIS AND TESTING (Continued)

(18) Inspect the electrical connector at the crank-
shaft position sensor (Fig. 45).
(19) Check the electrical connection at the vehicle
speed sensor (Fig. 46).(20) Check the electrical connection at the power
steering pressure switch on the power steering gear
housing (Fig. 47).
(21) On vehicles with automatic transaxles, check
the electrical connections at the park/neutral switch
and the torque convertor clutch solenoid (Fig. 48).
(22) Inspect the electrical connections at the
upstream and downstream heated oxygen sensors
(Fig. 49) and (Fig. 50).
(23) Inspect the fuel pump module electrical con-
nection at the fuel tank for corrosion or damage (Fig.
51). Check for pinched, kinked or damaged fuel sup-
ply tube.
(24) Inspect the connections to the speed control
servo, if equipped (Fig. 31). Refer to Group 8H, Vehi-
cle Speed Control.
(25) Inspect the connection at the battery temper-
ature sensor (Fig. 52).
Fig. 44 Generator
Fig. 45 Crankshaft Position Sensor
Fig. 46 Vehicle Speed Sensor
Fig. 47 Power Steering Pressure Switch
Fig. 48 Park/Neutral Switch and Torque Convertor
Clutch Solenoid
PLFUEL SYSTEM 14 - 39
DIAGNOSIS AND TESTING (Continued)