Description And Operation

DESCRIPTION 

This vehicle is equipped with the Atlantis bus architecture. 

The primary on-board communication network between 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 (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 several separate CAN bus systems used in the vehicle. They are designated:

• CAN-C
• CAN-C AT
• CAN-C EPT
• DIAGNOSTIC CAN-C
• CAN-CH
• DIAGNOSTIC CAN-CH
• CAN-IHS
• CAN-IHS AT
• DIAGNOSTIC CAN-IHS
• PRIVATE CAN

The CAN-C dominant nodes are:

1. Body Control Module (BCM)
2. Powertrain Control Module (PCM)

The CAN-CH dominant nodes are:

1. Occupant Restraint Controller (ORC)
2. Antilock Brake System (ABS) Module

The CAN-IHS dominant nodes are:

1. BCM
2. Instrument Panel Cluster (IPC)

The CAN-IHS and the CAN-C bus 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 CAN-IHS system uses the slower (125 Kbps) bus speed. The CAN-IHS system is used for communications between less critical nodes. This electronics architecture is called Atlantis.

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 BCM is located under the instrument panel to left of the steering column. The central CAN gateway or hub module integral to the BCM is connected to CAN-IHS and CAN-C buses. This gateway physically and electrically isolates the CAN buses from each other and coordinates the bidirectional transfer of messages between them.

CAN BUS SPLICE BLOCKS 

There are 19 different CAN BUS splice blocks located throughout this vehicle, and these are located so that they can be accessed. These are color coded for determining which splice connector belongs to which BUS network:

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 (up to 20 Kbps) serial link bus used to provide direct communication between a LIN master module, slave modules and certain switch or sensor inputs. Once the master module sends a request on the LIN bus, the slave modules have the capability of both sending and receiving information over LIN. 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.

OPERATION 

The primary communication network between electronic control modules on this vehicle is the CAN data bus system. The 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 Interior High Speed (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 certain bus network faults. These data communication network is known as the Atlantis  electronics bus architecture.

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.

When an open circuit or terminal push out occurs one or more modules can become isolated from the remainder of the bus. The isolated module will attempt to communicate, but will not be able to receive messages or determine arbitration from other modules. Each time the isolated module attempts to communicate it alters the bus voltage on the intact bus circuit. Without functioning arbitration the isolated module alters the bus voltage while other bus messages are being sent thereby corrupting the messages on the remainder of the bus.

The vehicle communication systems may be diagnosed with the Mopar Scope. Refer to COMMUNICATION - NON-DTC BASED DIAGNOSTICS .

CAN BUS FAULTS 

The communication protocol being used for the CAN data bus is a non-proprietary, open standard adopted from the Bosch CAN Specification 2.0b. The CAN-C is the faster of the two primary buses in the CAN bus system, providing near real-time communication (500 Kbps). CAN-IHS communicates at (125 Kbps).

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 bus (+) wire, while the other bus wire will carry a lower voltage and is referred to as the CAN bus (-) wire. Refer to the CAN Bus Voltages table.

The CAN 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. The BCM will keep either the CAN-IHS or the CAN-C bus awake for a timed interval after it receives a diagnostic message for that bus over the Diagnostic CAN-C bus.

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 also has two 64-bit registers, which track each of the as-built  and currently responding  nodes on the CAN-IHS and CAN-C buses. 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.

LIN 

The LIN communication network is a single-wire, low-speed network different from the CAN networks. The LIN bus is a Class A data bus system that uses a centralized module, called a Master module, often referred to as the Master module, with a series of other modules, called Slave modules, directly wired to it on a dedicated, single-wire circuit. The communication over a LIN bus only occurs between the Master and Slave modules. Each module on the LIN bus can provide bias. Once the master module sends a request on the LIN bus, the slave modules do have the capability of both sending and receiving information over LIN. Even though it is limited, the LIN bus simplifies wiring in a vehicle by combining multiple input and output circuits on a single bus wire. The LIN bus utilizes stub (backbone) topology.

The Master module is central to the LIN bus system. All LIN modules connect to a Master module through the LIN bus circuit. The Master module is also wired to a CAN bus for information sharing and to allow for scan tool diagnosis. The Master module is responsible for LIN diagnostics and is capable of setting fault codes for any LIN module or circuit faults. Since a Slave module cannot communicate with any other module directly, the Master module relays LIN Slave module data over the CAN bus to the scan tool, similar to a Gateway Module. Controlled module inputs and commands must be given only to the Master module, which then sends the information to another Slave module or out onto the CAN bus.

The LIN bus is biased through the Master and Slave modules. When at rest, the voltage on the LIN network is close to battery voltage. When LIN bus communication occurs, the voltage is pulled low to nearly 0V, creating a digital signal. If a Slave module is disconnected or removed from the network, that module no longer pulls voltage low on the LIN bus, and the average network voltage level will be lower. LIN voltage reads 12V when in sleep mode.The Master module communicates with Slave modules by pulling the voltage from high to low, creating a digital signal. Controlled modules communicate with the Master by biasing the network voltage in the same manner. Even though the LIN Slave modules are wired to each other, they only recognize the voltage pulses sent by the Master module, making communication possible only between the Slave and the Master. However, LIN communication can occur between Slave modules by using the Master module to relay information. The power feed to the LIN Slave is determined by its function. Controlled modules with a battery feed voltage supply operate and communicate even if the ignition is in the OFF position. For example, to support the hazard lamp function, the instrument panel switch bank is battery fed. If the LIN module only needs to function with the ignition ON, such as the compass module, the power feed is ignition only. The lighting and wiper multifunction switch require both feeds. This allows the lighting functions to be independent of ignition status, while the operation of the wipers requires the ignition feed. LIN Slave modules that receive their power feed from an ignition circuit enter sleep mode when the ignition power is removed. LIN Slave modules that receive their power from a direct battery feed receive a sleep message when the vehicle data bus enters sleep mode. For circuits where the LIN modules are battery fed, either the Master or the Slave module can wake the other. If the Slave module wakes up the Master, the vehicle bus also wakes.

As with any single-wire communication bus, a LIN bus has low fault tolerance. If a short to ground or power occurs on the LIN bus, the entire LIN bus loses the ability to communicate with the Master module. If an open occurs within the network, modules on the other side of the break (that are no longer connected to the Master module) lose communication. If an open occurs within the network, modules still connected to the Master module continue to communicate. Loss of power or ground to a Slave module results in that particular Slave module losing communication as well, whereas loss of power or ground to a Master module results in no LIN bus communication. Generally, one Slave module is triggered for information at a time - meaning zero collision risk and no need for arbitration as is used in CAN (Controller Area Network). If multiple Slave modules respond, a collision occurs and the Master ECU defaults to unconditional frames.

When the LIN bus is shorted, no modules can communicate on the network and a loss of all LIN module functionality occurs. Loss of communication codes (U-codes) will set in the Master module. A short to ground or to power on the LIN bus does not affect Master module communication over the CAN bus. The voltage on the LIN bus should be checked to see if voltage is present. Modules may be isolated by disconnecting Slave modules one at a time and then checking for LIN communication to return when a particular Slave is disconnected. When all Slave and Master modules are disconnected, test the LIN circuit for a short to ground or to power. If an open occurs, modules downstream of the open lose functionality and communication codes will set. If a single LIN Slave module is not communicating but all other LIN modules are functioning normally, always verify power, ground, and LIN voltage at the suspect module before replacing any parts. As long as at least one module on the LIN network is connected, then the circuit is able to be biased.