Description And Operation

DESCRIPTION 

This vehicle is equipped with the Powernet electronic architecture. 

The primary on-board communication network between Electronic Control Units (ECU) 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. These networks are protected by a Security Gateway Module (SGW).

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 (9.6 Kbps) serial link bus used to provide direct communication between a LIN master module and certain switch or sensor inputs.

There are actually two separate CAN bus systems used in the vehicle. They are designated: the CAN-Chassis (CAN-C) and the CAN-Interior High Speed (IHS). The CAN-C and CAN-IHS 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). The CAN-C is used typically for communications between more critical nodes, while the slower (125 Kbps). The CAN-IHS system is used for communications between less critical nodes.

• CAN-Chassis (CAN-C)
  • For a complete CAN C BUS LAYOUT wiring diagram, Refer to the appropriate wiring information   .
  • For a complete CAN C BUS SYSTEM wiring diagram, Refer to the appropriate wiring information   .
• CAN-Interior High Speed (CAN-IHS)
  • For a complete CAN IHS BUS LAYOUT wiring diagram, Refer to the appropriate wiring information   .
  • For a complete CAN IHS BUS SYSTEM wiring diagram, Refer to the appropriate wiring information   .

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 Body Control Module (BCM) is located under the instrument panel to right of the glove box. The central CAN gateway or hub module integral to the BCM is connected to CAN-C and CAN-IHS buses. This gateway physically and electrically isolates the CAN buses from each other and coordinates the bi-directional transfer of messages between them.

All modules transmit and receive messages over one of these buses. Data exchange between the modules is achieved by serial transmission of encoded data messages (a form of transmission in which data bits are sent sequentially, one at a time, over a single line). Each module can both send and receive serial data simultaneously. Each data bit of a CAN bus message is carried over the bus as a voltage differential between the two bus circuits which, when strung together, form a message. Each module uses arbitration to sort the message priority if two competing messages are attempting to be broadcast at the same time. Corruption of a single bit within a message will corrupt the entire message. Each message contains a Cyclic Redundancy Check (CRC) which specifies the message size exactly. If the message detected conflicts with the CRC the ECU receiving it will determine the message to be an error and consider that communication has not been possible. Diagnosis of this condition using a lab scope may reveal activity that appears to be Bus data messages even if no actual communication is possible. Communication problems that affect the whole bus, as a result of opens and terminal push outs are more likely to occur on data busses that operate at a high speed than a data bus that operates at a lower speed

LIN 

In addition to the CAN bus network, certain ECUs may also be equipped with a Local Interface Network (LIN) data bus. The LIN data bus is a single wire low-speed (9.6 Kbps) serial link bus used to provide direct communication between a LIN master module and certain switch or sensor inputs based on vehicle configuration. There is also a private security bus network between the Radio Frequency Hub (RFH) Module and the Keyless Ignition Node (KIN) known as the Security K Line Communication Bus.

Local Interconnect Network (LIN)
Master Module	CIRCUIT ID	Slave Module
Body Control Module (BCM) LIN 1	D401	Off Road Bank Switch		Upper Switch Bank			Intelligent Battery Sensor
Body Control Module (BCM) LIN 2	D402	Electronic Overhead Module		Inside Rear View Mirror			Compass Module
Body Control Module (BCM) LIN 3	D403	Steering Column Control Module			Inverter Module
Steering Column Control Module (SCCM)	D592	Speed Control Switch
	D594	Left Steering Wheel Switch

For a complete LIN BUS SYSTEM wiring diagram, Refer to the appropriate wiring information   .

OPERATION 

The Controller Area Network (CAN) data bus allows all electronic modules connected to the bus to share information with each other. Regardless of whether a message originates from a module on the higher speed CAN-C (500K) bus or on the lower speed CAN-IHS (125K) Bus the message structure and layout is similar, which allows the BCM to be a Central Gateway to process and transfer messages between the CAN-C and CAN-IHS buses. The BCM also stores Diagnostic Trouble Codes (DTCs) for bus networking faults.

The vehicle communication systems may be diagnosed with the Mopar Scope. Refer to DIAGNOSIS AND TESTING .

CAN BUS FAULTS 

TYPES OF CAN BUS FAULTS
LOSS OF COMMUNICATION	will set by an active receiving/reporting ECU on a CAN Bus network that detects no communication from another ECU on the same CAN Bus network. Insufficient power, ground, bus voltage, or inaccurate vehicle configuration will cause a loss of communication.
IMPLAUSIBLE MESSAGE	will set by an active receiving/reporting ECU, when it determines the data sent from the active transmitting/offending ECU is missing part of the message, or the message is an irrational value over the CAN Bus.
MISSING MESSAGE	will set by an active receiving/reporting ECU, when it determines a data message to be missing partial information when sent from the active transmitting/offending ECU over the CAN Bus network.
BUS OFF	set by an ECU that has experienced approximately 32 transmit errors, this can be caused by ECU internal faults as well as external bus faults like shorts or plugging and unplugging test tools to the diagnostic connector.
PHYSICAL	is only detectable by an ECU that has a transceiver that is able to detect shorts on the bus. If the ECU does not, it generally will set bus off faults due to shorted bus lines.

The CAN bus nodes are connected in parallel to the two-wire bus using a twisted pair, where the wires are wrapped around each other to provide shielding from unwanted electromagnetic induction, thus preventing interference with the relatively low voltage signals being carried through them. The twisted pairs have between 33 and 50 twists per meter (yard). While the CAN bus is operating (active), one of the bus wires will carry a higher voltage and is referred to as the CAN High or CAN bus (+) wire, while the other bus wire will carry a lower voltage and is referred to as the CAN Low or CAN bus (-) wire. Refer to the CAN Bus Voltages table.

CAN Bus Operational Voltages
CAN-C Bus Circuits	Sleep	Recessive (Bus Idle)	Dominant (Bus Active)	CAN-L Short to Ground	CAN-H Short to Ground	CAN-L Short to Battery	CAN-H Short to Battery	CAN-H Short to CAN-L
CAN-L (-)	0 V	2.3 - 2.5 V	1.3 - 2.3 V	0 V	0.3 - 0.5V	Battery Voltage	Battery Voltage Less 0.75 V	2.45 V
CAN-H (+)	0 V	2.5 - 2.7 V	2.6 - 3.5 V	0.02 V	0 V	Battery Voltage Less 0.75 V	Battery Voltage	2.45 V
CAN-IHS Bus Circuits	Key-Off (Bus Asleep)		Key-On (Bus Active)	CAN-L Short to Ground	CAN-H Short to Ground	CAN-L Short to Battery	CAN-H Short to Battery	CAN-H Short to CAN-L
CAN-L (-)	0.0V		1.3 - 2.3 V	0 V	0.3 - 0.5 V	Battery Voltage	Battery Voltage Less 0.75 V	2.45 V
CAN-H (+)	0.0 V		2.6 - 3.5 V	0.02 V	0 V	Battery Voltage Less 0.75 V	Battery Voltage	2.45 V
Notes
All measurements taken between node ground and CAN terminal with a standard DVOM.
Digital Voltmeter (DVOM) will display average network voltage.
Total resistance of CAN networks can be measured with the battery disconnected. The average resistance is approximately 60 Ohms. The termination resistors are integral to the Star Connectors.

The CAN-IHS bus network remains active until all nodes on that network are ready for sleep. This is determined by the network using tokens in a manner similar to polling. When the last node that is active on the network is ready for sleep, and it has already received a token indicating that all other nodes on the bus are ready for sleep, it broadcasts a bus sleep acknowledgment  message that causes the network to sleep. Once the CAN-IHS bus network is asleep, any node on the bus can awaken it by transmitting a message on the network.

In the CAN system, available options are configured into the BCM at the assembly plant, but additional options can be added in the field using the diagnostic scan tool. The configuration settings are stored in non-volatile memory.

The BCM stores a Diagnostic Trouble Code (DTC) in one of two caches for any detected active or stored faults in the order in which they occur. One cache stores powertrain (P-Code), chassis (C-Code) and body (B-Code) DTCs, while the second cache is dedicated to storing network (U-Code) DTCs.