Steering - Dodge RAM 1500 1998 Owner's Manual

8E - 10 ELECTRONIC CONTROL MODULES
POWERTRAIN CONTROL MODULE (Continued)
WIDE OPEN THROTTLE MODE
This is an Open Loop mode. During wide open
throttle operation, the PCM receives the following
inputs.
• Battery voltage
• Crankshaft position sensor
• Engine coolant temperature sensor
• Intake manifold air temperature sensor
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Camshaft position sensor signal
During wide open throttle conditions, the following
occurs:
• Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then control
the injection sequence and injector pulse width by
turning the ground circuit to each individual injector
on and off. The PCM ignores the oxygen sensor input
signal and provides a predetermined amount of addi-
tional fuel. This is done by adjusting injector pulse
width.
• The PCM adjusts ignition timing by turning the
ground path to the coil(s) on and off.
IGNITION SWITCH OFF MODE
When ignition switch is turned to OFF position,
the PCM stops operating the injectors, ignition coil,
ASD relay and fuel pump relay.
DESCRIPTION - 5 VOLT SUPPLIES
Two different Powertrain Control Module (PCM)
five volt supply circuits are used; primary and sec-
ondary.
DESCRIPTION - IGNITION CIRCUIT SENSE
This circuit ties the ignition switch to the Power-
train Control Module (PCM).
DESCRIPTION - POWER GROUNDS
The Powertrain Control Module (PCM) has 2 main
grounds. Both of these grounds are referred to as
power grounds. All of the high-current, noisy, electri-
cal devices are connected to these grounds as well as
all of the sensor returns. The sensor return comes
into the sensor return circuit, passes through noise
suppression, and is then connected to the power
ground.
The power ground is used to control ground cir-
cuits for the following PCM loads:
• Generator field winding
• Fuel injectors
• Ignition coil(s)
• Certain relays/solenoids
• Certain sensors
DESCRIPTION - SENSOR RETURN
The Sensor Return circuits are internal to the Pow-
ertrain Control Module (PCM).
Sensor Return provides a low–noise ground refer-
ence for all engine control system sensors. Refer to
Power Grounds for more information.
OPERATION
OPERATION - PCM
The PCM operates the fuel system. The PCM is a
pre-programmed, triple microprocessor digital com-
puter. It regulates ignition timing, air-fuel ratio,
emission control devices, charging system, certain
transmission features, speed control, air conditioning
compressor clutch engagement and idle speed. The
PCM can adapt its programming to meet changing
operating conditions.
The PCM receives input signals from various
switches and sensors. Based on these inputs, the
PCM regulates various engine and vehicle operations
through different system components. These compo-
nents are referred to as Powertrain Control Module
(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, power
steering pump pressure, and the brake switch.
The PCM adjusts idle speed based on inputs it
receives from sensors that react to: throttle position,
vehicle speed, transmission gear selection, engine
coolant temperature and from inputs it receives from
the air conditioning clutch switch and brake switch.
Based on inputs that it 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:
• ABS module (if equipped)
• A/C request (if equipped with factory A/C)
• A/C select (if equipped with factory A/C)
• A/C pressure transducer
• Auto shutdown (ASD) sense
• Battery temperature sensor
• Battery voltage
• Brake switch
• J1850 bus (+) circuits
• J1850 bus (-) circuits
• Camshaft position sensor signal
• Crankshaft position sensor
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