Module Communications Network: Other Ford Fiesta Mk6

Network Termination

The CAN uses a network termination circuit to improve communication reliability. The network termination of the CAN bus occurs inside the termination modules by termination resistors. Termination modules are located at either end of the bus 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 a 120 ohm resistor across the positive and negative bus connection in the termination module. With 2 termination modules on each network, and the 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 Module

The IPC is the gateway module, translating HS-CAN to MS-CAN and vice versa. The FCDIM is the gateway module, translating MS-CAN to ICAN and vice versa, allowing a message to be distributed throughout the three networks. The IPC and the FCDIM are the only modules on this vehicle that have this ability.

SPECIAL TOOLS Fluke 77-IV Digital Multimeter FLU77-4 or equivalent Vehicle Communication Module (VCM) and Integrated Diagnostic System (IDS) software with appropriate hardware, or equivalent scan tool Flex Probe Kit NUD105-R025D or equivalent

Scheme 115

Controller Area Network (CAN) Fault Tolerance

Note. The oscilloscope traces below are from the Integrated Diagnostic System (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.

Traces below are viewed at 500mV per division (vertical axis) and 20 microseconds (20μs) per division (horizontal axis). Readings taken with a different oscilloscope vary from those shown in illustration. Compare any suspect readings to a known good vehicle.

Scheme 116

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 DTCs (U-codes) to set or may cause a complete network outage.

Scheme 117

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.

Scheme 118

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.

Scheme 119

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.

Scheme 120

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.

Scheme 121

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.

Scheme 122

Rhythmic oscillations, inductive spikes or random interference can disrupt 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 in illustration 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

Modules on the CAN utilize simultaneous communication of 2 or more messages on the same network circuits. The following chart summarizes the messages sent and received on the network.

CAN Module Communication Message Chart

Note. This chart describes the specific HS-CANand MS-CANmessages broadcast by each module, and the module(s) that receive the message.

Note. For the ICAN, 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 INFORMATION AND ENTERTAINMENT SYSTEMS .

CAN MODULE COMMUNICATION MESSAGE CHART