Durango RT 4WD V8-5.9L VIN Z LDC (2002)
Information Bus: Description and Operation
VEHICLE COMMUNICATION
The Programmable Communication Interface (PCI) data bus system is a single wire multiplex system used for vehicle communications. Multiplexing
is a system that enables the transmission of binary encoded messages shared between multiple modules over a single channel or circuit.
The PCI bus circuit is identified as D25 and is violet with a yellow tracer. Additional tracer colors may be added to the yellow in order to distinguish
between different module connections. The modules are wired in parallel. Connections are made in the harness using a splice.
The splice called the Diagnostic Junction Port, serves as the "hub" of the bus. The Diagnostic Junction Port provides an access point to isolate most of
the modules on the bus in order to assist in diagnosing the circuit.
Many of the control modules in a vehicle require information from the same sensing device. Multiplexing reduces wire harness complexity, sensor
current loads and controller hardware because each sensing device is connected to only one controller, which reads and distributes the sensor
information to the other controllers over the data bus. Also, because each controller on the data bus can access the controller sensor inputs to every
other controller on the data bus, more function and feature capabilities are possible.
A multiplex system allows the information flowing between controllers to be monitored using a diagnostic scan tool. This system allows a control
module to broadcast message data out onto the bus where all other control modules can read the messages that are being sent. When a module reads a
message on the data bus that it requires, it relays that message to its microprocessor. Each module ignores the messages on the data bus that it doesn't
recognize.
The following modules are used on the DN:
-
Airbag Control Module
-
Left Side Impact Airbag Control Module
-
Right Side Impact Airbag Control Module
-
A/C Heater Control
-
Amplifier
-
Central Timer Module
-
Controller Antilock Brake
-
Compass Mini-Trip Computer
-
Electro/Mechanical Instrument Cluster
-
Powertrain Control Module
-
Radio
-
Sentry Key Immobilizer Module
-
Transfer Case Control Module
-
Transmission Control Module
Data exchange between modules is achieved by serial transmission of encoded data over this single wire broadcast network. The PCI data bus
messages are carried over the bus in the form of Variable Pulse Width Modulated (VPWM) signals. The PCI data bus speed is an average 10.8
Kilo-bits per second (Kbps).
The voltage network used to transmit and receive messages requires biasing and termination. Each module on the PCI data bus system provides its
own biasing and termination in order to transmit and receive messages. Each module (also referred to as a node) terminates the bus through a
terminating resistor and a terminating capacitor. The Powertrain Control Module (PCM) is the only dominant node for the PCI data bus system.
The PCI bus uses low and high voltage levels to generate signals. The bus voltage is at zero volts when no modules are transmitting and is pulled up
to about 7-1/2 volts when modules are transmitting. The low and high voltage levels are generated by means of variable-pulse width modulation to
form signals of varying length.
When a module is transmitting on the bus, it is reading the bus at the same time to ensure message integrity.
Each module is capable of transmitting and receiving data simultaneously.
The PCI data bus can be monitored using the DRBIII scan tool. It is possible for the bus to pass all DRBIII tests and still be faulty if the voltage
parameters are all within the specified range and false messages are being sent.