Chrysler neon 1997 Service Manual page 1320

VEHICLE SPEED SENSOR
PL
DESCRIPTION AND OPERATION (Continued)
VEHICLE SPEED SENSOR—PCM 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.
The vehicle speed sensor generates 8 pulses per sen-
sor revolution. These signals, in conjunction with a
closed throttle signal from the throttle position sensor,
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:
• Speedometer
• Speed control
• Daytime Running Lights (Canadian Vehicles only).
Fig. 20 Vehicle Speed Sensor—Automatic
Transmission
AIR CONDITIONING CLUTCH RELAY—PCM
OUTPUT
The PCM controls the air conditioning clutch relay
ground circuit. Buss bars in the Power Distribution
Center (PDC) supply voltage to the solenoid side and
power side of the relay. 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 disables the A/C com-
pressor clutch for several seconds.
TRANSAXLE
EXTENSION
TRANSAXLE
HOUSING
Fig. 21 Vehicle Speed Sensor—Manual
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 RELAY—PCM 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 LAMP—PCM
OUTPUT
The PCM turns the instrument panel Charging
System Lamp on. Refer to Group 8C for charging sys-
tem information.
SPEED SENSOR RETAINING BOLT
FUEL SYSTEM
Transmission
SPEED SENSOR
14 - 33