Dodge ram truck 3500 1996 Service Manual page 1351

e n
FUEL SYSTEM 14 - 117
DESCRIPTION AND
O P E R A T I O N
fContinued)
Depending upon intake manifold air temperature,
engine rpm and predetermined PCM values, one or
both of the relays and one or both of the heating ele­
ments may be activated. This may be observed as a
large needle swing on the vehicle voltmeter and is
due to the high-amperage draw of the heating ele­
ments. Each heating element will draw approxi­
mately 95 amps at 12 volts. This voltmeter
movement is a normal condition during the
post-heat cycle.
Refer to the following Air Heater Cycle Chart (Fig.
7) for a temperature/time comparison of relay
engagement.
The PCM is also programmed with battery saving
features. I t will shut down the air heater relays if:
• the engine starter is operated during the pre­
heat cycle.
• the engine stalls during the post-heat cycle.
• the engine starter is operated for more than 10
seconds during the post-heat cycle.
• the vehicle speed is above 10 mph during the
post-heat cycle.
The post-heat cycle will continue for up to 3 1/2
minutes unless the PCM determines one or more of
these preceding features interrupts the cycle strat­
egy.
lEimRAIURE-
PK4€1T€¥QI11IE
« N m 0 N 0 l i B « M I
^ ^ ^ ^
BNmONONr
Above 15°C
(59° F)
0 seconds
No
-10°Cto 15° C
(15° F to 59° F)
10 seconds
Yes
-18° C to -10° F
(0° Fto 15°
F)
15 seconds Yss
Below-18° C
(0°
F)
30 seconds Yes
J9414-133
Fig. 7 Air Heater Cycle Chart
SPEED CONTROL SWITCH—PCM INPUT
Six different speed control functions, using three
momentary contact switches, are monitored through
this multiplexed input. The resistance monitored at
this input, in combination with the length of time the
PCM measures the resistance, determines which
switch feature has been selected. The three switches
are: On/Off, Set/Coast and Resume/Accelerate.
The speed control operating range is from approx­
imately 56 km/h to 137 km/h (35 to 85 mph). Inputs
that effect speed control operation are:
• Brake switch position
• Park/neutral switch
• Vehicle speed sensor
• Engine speed sensor
• Throttle position sensor (auto, trans, only)
Refer to Group 8H for further speed control infor­
mation.
PARK/NEUTRAL POSITION SWITCH—PCM INPUT
The park/neutral switch provides an input to the
powertrain control module (PCM). This will indicate
that the automatic transmission is in Park, Neutral
or a Drive gear selection. This input is used to deter­
mine speed control strategy and electrical operation
of both the overdrive and torque convertor solenoids.
Refer to Group 21, Transmissions, for testing,
replacement and adjustment information.
THROTTLE POSITION SENSOR—PCM INPUT
The throttle position sensor (TPS) is used only on
vehicles equipped with an automatic transmission i f
equipped with a diesel engine. I t is not used with the
manual transmission.
The TPS is mounted on the side of the fuel injec­
tion pump (Fig. 8). The TPS provides an input to the
PCM. I t senses how far the throttle is open (past the
idle position). The PCM uses the TPS input, along
with vehicle speed sensor and engine speed sensor
inputs to determine 3-4 upshift (overdrive) and 4-3
downshift. I t is also used with the vehicle speed sen­
sor and engine speed sensor inputs to engage and
disengage the torque convertor solenoid. This sole­
noid is used for torque convertor engagement.
The TPS is a linear potentiometer. The PCM sup­
plies 5 volts to the sensor. TPS output voltage to the
PCM will vary. At idle speed, the voltage should be
1.0 volt (± .2 volts). At wide open throttle (WOT), the
output voltage must be 2.2-to-2.9 volts higher than at
idle speed.
TRANSMISSION TEMPERATURE SENSOR—PCM
INPUT
DIESEL WITH AUTOMATIC TRANSMISSIONS
ONLY
The transmission temperature sensor is a variable,
thermistor type. I t reacts to temperature changes. At
cold transmission oil temperatures, its resistance is
high. As temperatures increase, its resistance will
decrease.