Communications Network
Communications Network
Principles of Operation
The High Speed Controller Area Network (HS-CAN) operates at a maximum data transfer speed of 500 Kbps and is designed for real time powertrain information transfer and control. Modules on the HS-CAN (High Speed Controller Area Network) communicate using bussed messages. The HS-CAN (High Speed Controller Area Network) uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, the HS-CAN (High Speed Controller Area Network) allows sharing of information between all modules on the network.
The Medium Speed Controller Area Network (MS-CAN) operates at a maximum data transfer speed of 125 Kbps for bus messages and is designed for general information transfer. Modules on the MS-CAN (Medium Speed Controller Area Network) communicate using bussed messages. The MS-CAN (Medium Speed Controller Area Network) uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, the MS-CAN (Medium Speed Controller Area Network) allows sharing of information between all modules on the network.
The Infotainment Controller Area Network (I-CAN) operates at a maximum data transfer speed of 500 Kbps and is designed for real time audio and multimedia information transfer and control. Modules on the I-CAN (Infotainment Controller Area Network) communicate using bussed messages. The I-CAN (Infotainment Controller Area Network) uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. The I-CAN (Infotainment Controller Area Network) allows sharing of information between all modules on the network. The I-CAN (Infotainment Controller Area Network) is connected to the Data Link Connector (DLC), but the I-CAN (Infotainment Controller Area Network) modules communicate with the scan tool over the HS-CAN (High Speed Controller Area Network). The Instrument Panel Cluster (IPC) is used as a gateway module for the messages to transfer between the scan tool and the modules on the I-CAN (Infotainment Controller Area Network).
Controller Area Network (CAN) Fault Tolerance
NOTE: The oscilloscope traces below are from the Integrated Diagnostic System (IDS) oscilloscope taken using the IDS (Integrated Diagnostic System) pre-configured CAN (Controller Area Network) 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.
Traces below are viewed at 500mV per division (vertical axis) and 20 microseconds (20micros) per division (horizontal axis). Readings taken with a different oscilloscope vary from those shown. Compare any suspect readings to a known good vehicle.
Normal CAN (Controller Area Network) Operation
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 (Controller Area Network) waveform may cause network DTCs (U-codes) to set or may cause a complete network outage.
CAN (Controller Area Network) 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 (Controller Area Network) (+) 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 (Controller Area Network) (-) 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 (Controller Area Network) (+) 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 (Controller Area Network) (-) 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 (Controller Area Network) 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
NOTE: Some HS-CAN (High Speed Controller Area Network) faults may result in a no-start condition.
NOTE: For the I-CAN (Infotainment Controller Area Network), message mapping is not essential to diagnostics as the symptoms arising from a message error are all related to the audio system. For audio system concerns, refer to Accessories and Optional Equipment.
Controller Area Network (CAN) Module Communication Message Chart
