Dakota 2WD V8-4.7L Flex Fuel (2009)
Information Bus: Description and Operation
Communication - Description
DESCRIPTION
The primary on-board communication network between microprocessor-based electronic control modules in this vehicle is the Controller Area Network
(CAN) data bus system. A data bus network minimizes redundant wiring connections; and, at the same time, reduces wire harness complexity, sensor
current loads and controller hardware by allowing each sensing device to be connected to only one module (also referred to as a node). Each node reads,
then broadcasts its sensor data over the bus for use by all other nodes requiring that data. Each node ignores the messages on the bus that it cannot use.
The CAN bus is a two-wire multiplex system. Multiplexing is any system that enables the transmission of multiple messages over a single channel or
circuit. The CAN bus is used for communication between all vehicle nodes. However, in addition to the CAN bus network, certain nodes may also be
equipped with a dedicated Serial Controller Interface (SCI) or a K-Line serial link bus to provide direct communication between that node and certain
sensor inputs.
There are actually three separate CAN bus systems used in the vehicle. They are designated: the CAN-B, the CAN-C and the Diagnostic CAN-C. The
CAN-B and CAN-C systems provide on-board communication between all of the nodes that are connected to them. The CAN-C is the faster of the two
systems providing near real-time communication (500 Kbps), but is less fault tolerant than the CAN-B system. The CAN-C is used typically for
communications between more critical nodes, while the slower (83.3 Kbps), but more fault tolerant CAN-B system is used for communications between
less critical nodes. The CAN-B fault tolerance comes from its ability to revert to a single wire communication mode if there is a fault in the bus wiring.
The added speed of the CAN data bus network is many times faster than previous data bus systems. This added speed facilitates the addition of more
electronic control modules or nodes and the incorporation of many new electrical and electronic features in the vehicle.
The Diagnostic CAN-C bus is also capable of 500 Kbps communication, and is sometimes informally referred to as the CAN-D system to differentiate it
from the other high speed CAN-C bus. The Diagnostic CAN-C is used exclusively for the transmission of diagnostic information between the Front
Control Module (FCM) and a diagnostic scan tool connected to the industry-standard 16-way Data Link Connector (DLC) located beneath the instrument
panel on the driver side of the vehicle.
All vehicles have a Central Gate Way (CGW or FCMCGW) or hub module integral to the FCM that is connected to all three CAN buses. This gateway
physically and electrically isolates the CAN buses from each other and coordinates the bi-directional transfer of messages between them.
