Compass 2WD L4-2.0L VIN 0 (2007)
Body Control Systems: Description and Operation
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 most vehicle nodes. However, in addition to the CAN bus network, certain nodes may also be
equipped with a Local Interface Network (LIN) data bus. The LIN data bus is a single wire low-speed system used to provide direct communication
between a master module and certain switch or 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 nodes in the vehicle. 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 exclusively for communications between
critical powertrain and chassis nodes. The slower (83.3 Kbps), but more fault tolerant CAN-B system is used for communications between body and
interior 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 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 Totally Integrated Power Module/Central GateWay
(TIPM or TIPMCGW) 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.
The TIPM is located in the engine compartment near the battery. The central CAN gateway or hub module integral to the TIPM 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.
