Dodge RAM TRUCK 1500 1995 Service Manual page 1172

14 - 90 COMPONENT DESCRIPTION/SYSTEM OPERATION—DIESEL ENGINE
WATER-IN-FUEL SENSOR—PCM PIN #1—PCM
INPUT
The water-in-fuel (WIF) sensor is located at the
bottom of the fuel filter/water separator (Fig. 3).
FUEL FILTER/
DRAIN
VALVE
J9414-90
Fig. 3 Water-in-Fuel Sensor
WAIT-TO-
START
WARNING LAMP
HEAT-A/C
TEMPERATURE
' CONTROL
KNOB
WARNING LAMP WARNING LAMP J9414-63
Fig. 4 Wait-to-Start and Water-in-Fuel Warning Lamp
Location
The sensor sends an input to the powertrain con­
trol module (PCM) when it senses water in the fuel
filter/water separator. As the water level in the filter/
separator increases, the resistance across the WIF
sensor decreases. This decrease in resistance is sent
as a signal to the PCM and compared to a high water
standard value. Once the value reaches 30 to 40 ki-
lohms, the PCM will activate the instrument panel
mounted, water-in-fuel warning lamp (Fig. 4). This
all takes place when the ignition key is initially put
in the ON position. The PCM continues to monitor
the input at the end of the intake manifold air heater
post-heat cycle.
BATTERY VOLTAGE—PCM PIN #3—PCM INPUT
The battery voltage input provides power to the
powertrain control module (PCM). It also informs the
PCM what voltage level is being supplied by the gen­
erator once the vehicle is running.
The battery input also provides the voltage that is
needed to keep the PCM memory alive. The memory
stores diagnostic trouble code (DTC) messages, mini­
mum and maximum TPS value from the previous
key-on and speed control adaptive memory.
BATTERY TEMPERATURE SENSOR
This input is internal to the powertrain control
module (PCM). A thermistor located within the
PCM's printed circuit board is used to sense under­
hood temperature. This temperature is used to vary
the battery charging rate in relationship to the tem­
perature.
SENSOR RETURN—PCM PIN #4—PCM INPUT
Sensor Return provides a low noise ground refer­
ence for all system sensors.
FIVE VOLT POWER—PCM PIN #6—PCM INPUT
This circuit supplies approximately 5 volts to power
the throttle position sensor (TPS) sensor.
EIGHT VOLT POWER—PCM PIN #7—PCM INPUT
This circuit supplies approximately 8 volts to power
the vehicle speed and engine speed sensors.
IGNITION CIRCUIT SENSE—PCM PIN #9—PCM
INPUT
The ignition circuit sense input tells the powertrain
control module (PCM) the ignition switch has been
turned to the ON position. Refer to the wiring dia­
grams for circuit information.
POWER GROUND—PCM PIN #11
Provides a common ground for power devices (sole­
noid and relay devices).
POWER GROUND—PCM PIN # 1 2
Provides a common ground for power devices (sole­
noid and relay devices).
INTAKE MANIFOLD AIR HEATER
The intake manifold air heater block/element as­
sembly is located on the top of the intake manifold
(Fig.
5).
The air heater is used to heat incoming air to the
intake manifold to help engine starting and improve
driveability with cool or cold outside temperatures.