Dodge ram truck 3500 1996 Service Manual page 1263

BR FUEL SYSTEM 14 29
DESCRIPTION AND OPERATION (Continued)
(PCM) Outputs. The sensors and switches that pro­
vide Inputs to the PCM are considered Powertrain
Control Module (PCM) Inputs.
The PCM adjusts Ignition timing based upon
inputs It receives from sensors that react to: engine
rpm, manifold absolute pressure, engine coolant tem­
perature, throttle position, transmission gear selec­
tion (automatic transmission), vehicle speed and the
brake switch.
The PCM adjusts idle speed based on inputs i t
receives from sensors that react to: throttle position,
vehicle speed, transmission .gear selection, engine
coolant temperature and from Inputs i t receives from
the air conditioning clutch switch and brake switch.
Based on inputs that i t receives, the PCM adjusts
ignition coil dwell. The PCM also adjusts the gener­
ator charge rate through control of the generator
field and provides speed control operation.
NOTE: PCM Inputs;
• Generator output
© A/C request (if equipped with factory A/C)
@ A/C select (if equipped with factory A/C)
• Auto shutdown (ASD) sense
• Intake manifold air temperature sensor
• Battery voltage
• Brake switch
• Engine coolant temperature sensor
• Crankshaft position sensor
• Ignition circuit sense (Ignition switch in run
position)
• Manifold absolute pressure (MAP) sensor
® Overdrive/override switch
• Oxygen sensor
• Park/neutral switch (auto, trans, only)
© SCI receive (DRB scan tool connection)
• Speed control resume switch
• Speed control set switch
• Speed control on/off switch
• Camshaft position sensor signal
• Throttle position sensor
• Vehicle speed sensor
• Sensor return
© Power ground
• Signal ground
NOTE: PCM Outputs;
• A/C clutch relay
• Idle air control (IAC) motor
• Auto shutdown (ASD) relay
© Generator field
• Malfunction indicator lamp (Check engine lamp)
• EGR valve control solenoid
• Fuel injectors
• Fuel pump relay
• Ignition coil
© EVAP canister purge solenoid
• SCI transmit (DRB scan tool connection)
• Speed control vacuum solenoid
® Speed control vent solenoid
• Tachometer (on instrument panel, If equipped)
The powertrain control module (PCM) contains a
voltage convertor. This converts battery voltage to a
regulated 5.0 volts. I t Is used to power the crankshaft
position sensor, camshaft position sensor and vehicle
speed sensor. The PCM also provides a five (5) volt
supply for the manifold absolute pressure (MAP) sen­
sor and throttle position sensor (TPS).
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
REQUEST SiGMAL: 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
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) RELAY—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) (Fig.
2). Refer to label on PDC cover for relay location. The
relay is used to connect the oxygen sensor heater ele­
ment, ignition coil, generator field winding and fuel
injectors to 12 volt + power supply.
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