Dodge ram truck 3500 1996 Service Manual page 1348

14 -114 FUEL SYSTEM BR
DESCRIPTION A N D OPERATION (Continued)
After inputs are received by the PCM, certain sen­
sors, switches and components are controlled or reg­
ulated by the PCM. These are considered PCM
Outputs. These outputs are for:
• A/C clutch relay (A/C clutch operation)
• Auto shutdown (ASD) relay
• Data link connectors (for DRB and MDS test
equipment)
• Generator field (charging system operation)
• Malfunction indicator lamp (check engine lamp)
• Overdrive solenoid electrical operation (auto,
trans, only)
• Overdrive/Override warning lamp (auto, trans,
only)
• SCI transmit (DRB scan tool connection)
• Speed control vacuum solenoid
• Speed control vent solenoid
• Tachometer
• Torque convertor electrical operation (auto,
trans, only)
• Transmission oil temperature warning lamp
(auto, trans, only)
• Wait-to-start lamp
• Water-in-fuel lamp
• Intake Manifold Air Heater Element #1
• Intake Manifold Air Heater Element #2
AIR CONDITIONING (A/C) CONTROLS—PCM INPUT
The A/C control system information applies to fac­
tory installed air conditioning units.
A/C SELECT SIGNAL^ When the A/C switch is in
the ON position, an input signal is sent to the pow­
ertrain control module (PCM). The signal informs the
PCM that the A/C has been selected. The PCM
adjusts idle speed to a pre-programmed rpm through
the idle air control (IAC) motor to compensate for
increased engine load.
A/C BEQUEST SIGNAL: Once A/C has been
selected, the powertrain control module (PCM)
receives the A/C request signal from the evaporator
switch. The input indicates that the evaporator tem­
perature is in the proper range for A/C application.
The PCM uses this input to cycle the A/C compressor J
clutch (through the A/C relay). I t will also determine
the correct engine idle speed through the idle air con­
trol (IAC) motor position.
If the A/C low-pressure switch opens (indicating a
low refrigerant level), the PCM will not receive an
A/C receive signal. The PCM will then remove the
ground from the A/C relay. This will deactivate the
A/C compressor clutch.
If the evaporator switch opens, (indicating that
evaporator is not in proper temperature range), the
PCM will not receive the A/C request signal. The
PCM will then remove the ground from the A/C relay,
deactivating the A/C compressor clutch.
AUTOMATIC SHUTDOWN (ASD) SENSE—PCM
INPUT
A 12 volt signal at this input indicates to the PCM
that the ASD has been activated. The ASD relay is
located in the power distribution center (PDC). The
PDC is located in the engine compartment. For the
location of the relay within the PDC, refer to PDC
cover.
This input is used only to sense that the ASD relay
is energized. I f the powertrain control module (PCM)
does not see 12 volts + at this input when the ASD
should be activated, i t will set a diagnostic trouble
code (DTC).
BATTERY VOLTAGE—PCM INPUT
The battery voltage input provides power to the
powertrain control module (PCM). I t 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—PCM INPUT
Provides a signal to the PCM corresponding to the
battery temperature. Refer to Group 8C, Charging
System for additional information.
BRAKE SWITCH—PCM INPUT
When the brake light switch is activated, the pow­
ertrain control module (PCM) receives an input indi­
cating that the brakes are being applied. After
receiving this input, the PCM is used to control the
speed control system. I t is also used for electrical
operation of the transmission torque converter.
ENGINE SPEED SENSOR—PCM INPUT
The engine speed (rpm) sensor is mounted to the
front of engine (Fig. 2). I t generates an rpm signal to
the PCM. The engine speed sensor input is used
along with the vehicle speed sensor and throttle posi­
tion sensor (TPS) inputs to determine when to shift
the automatic transmission into and out of overdrive.
The speed sensor signal is also used as an input for
the ASD relay (for control of generator field), vehicle
speed control, torque convertor electrical engagement
and instrument panel mounted tachometer.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR—
PCM INPUT
The intake manifold air temperature sensor is a
variable, thermistor type. I t reacts to temperature
changes. At cold air temperatures, its resistance is