Communications Network - System Operation and Component Description

System Operation

System Diagram

  Module Network Chart

Network Termination

The CAN uses network termination to improve communication reliability. Termination modules are located at both ends of the network. As network messages are broadcast in the form of voltage signals, the network voltage signals are stabilized by the termination resistors.

Each termination module has an internal 120 ohm resistor that bridges across the positive and negative bus connection. With two 120 ohm resistors located in a parallel circuit configuration, the total network impedance, or total resistance, is 60 ohms.

Network termination improves bus message reliability by stabilizing bus voltage and eliminating electrical interference.

Gateway Modules

NOTE: The GWM , communicates with the 4 controller area networks (CAN). The OBD DLC is fitted to the GWM , and is the direct interface with the scan tool.

The GWM is mounted under the driver side instrument panel. The OBD connector is fitted to the GWM . The GWM acts as a central gateway to translate messages across all 4 vehicle controller area networks (CAN), and vice versa. The GWM is the only module on this vehicle with this ability.

High Speed Controller Area Network 1 and 2 (HS1-CAN, HS2-CAN)

The HS1-CAN and HS2-CAN operate at a maximum data transfer speed of 500 Kbps and are designed for real time powertrain and driver feature information transfer and control. Modules on the HS1-CAN and HS2-CAN communicate using bussed messages. The HS-CAN uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, the HS-CAN allows sharing of information between all modules on each HS-CAN.

With the addition of more modules, network traffic has increased. This has created the need for an additional HS-CAN to manage the increased bus data carried on each network.

The GWM is used as a gateway for the messages to transfer between the scan tool and the modules on the HS1-CAN and the modules on the HS2-CAN.

The scan tool communicates with the vehicle communication networks directly through the HS1-CAN and HS2-CAN.

High Speed Controller Area Network 3 (HS3-CAN)

The HS3-CAN, or the infotainment controller area network (I-CAN), operates at a maximum data transfer speed of 500 Kbps and is designed for real time audio, multimedia and driver information transfer and control. Modules on the HS3-CAN communicate using bussed messages. HS3-CAN uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits, and allows sharing of information between all modules on the network.

The GWM is used as a gateway for the messages to transfer between the scan tool and the modules on the HS3-CAN.

The GWM translates the diagnostic messages from the HS2-CAN to the HS3-CAN and vice versa, allowing communication between the modules on the HS3-CAN and the scan tool.

Medium Speed Controller Area Network (MS-CAN)

The MS-CAN operates at a maximum data transfer speed of 125 Kbps and is designed for general information transfer. Modules on the MS-CAN communicate using bussed messages. The MS-CAN uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, the MS-CAN allows sharing of information between all modules on the network.

The GWM is used as a gateway for the messages to transfer between the scan tool and the modules on the MS-CAN.

The GWM translates the diagnostic messages from the HS2-CAN to the MS-CAN and vice versa, allowing communication between the modules on the MS-CAN and the scan tool.

Controller Area Network (CAN) Fault Tolerance

Fault Tolerance Normal Operation

NOTE: The oscilloscope traces shown are from the IDS oscilloscope taken using the IDS pre-configured CAN settings. The traces are for both data (+) and data (-) taken simultaneously (2-channel) at a sample rate of 1 mega-sample per second (1MS/s) or greater.

The data (+) and data (-) circuits are each regulated to approximately 2.5 volts during neutral or rested network traffic. As messages are sent on the data (+) circuit, voltage is increased by approximately 1.0 volt. Inversely, the data (-) circuit is reduced by approximately 1.0 volt when a message is sent.

Successful communication of a message can usually be identified by the slight spike at the end of a message transmission. Any signals that are significantly different than the normal CAN waveform may cause network Diagnostic Trouble Codes (DTCs) (U-codes) to set or may cause a complete network outage.

CAN Circuits Shorted Together

In the event the data (+) and data (-) circuits become shorted together, the signal stays at base voltage (2.5V) continuously and all communication capabilities are lost.

CAN (+) Circuit Shorted to Ground

In the event the data (+) circuit becomes shorted to ground, both the data (+) and data (-) circuits are pulled low (0V) and all communication capabilities are lost.

CAN (-) Circuit Shorted to Ground

In the event the data (-) circuit becomes shorted to ground, the data (-) circuit is pulled low (0V) and the data (+) circuit reaches near-normal peak voltage (3.0V) during communication but falls to 0V instead of normal base voltage (2.5V). Communication may continue but at a degraded level.

CAN (+) Circuit Shorted to Battery Voltage

In the event the data (+) circuit becomes shorted to battery voltage, the data (+) circuit is pulled high (12V) and the data (-) circuit falls to abnormally high voltage (above 5V) during communication and reaches battery voltage (12V) for peak voltage. Communication may continue but at a degraded level.

CAN (-) Circuit Shorted to Battery Voltage

In the event the data (-) circuit becomes shorted to battery voltage, both the data (+) and data (-) circuits are pulled high (12V) and all communication capabilities are lost.

CAN Circuit Signal Corruption

Rhythmic oscillations, inductive spikes or random interference can corrupt the network communications. The corruption signal source may be outside electrical interference such as motors or solenoids or internal interference generated from a module on the network. In some cases, an open in either the data (+) or data (-) circuit to a network module may cause the module to emit interference on the one circuit which is still connected. The trace shown is an example of a "sawtooth" pattern transmitted from a module with one open network circuit.

Other corruptions may be present when a module is intermittently powered up and down. The module on power up may initiate communication out of sync with other modules on the network causing momentary communication outages.

Controller Area Network (CAN) Multiplex Messages

  Communication Message Chart

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