Module Communications Network: Other Ford Focus I facelift

Network Termination

The CAN uses a network termination circuit to improve communication reliability. The network termination of the CAN bus takes place 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 two 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

1. stabilizing bus voltage.
2. eliminating electrical interference.

Special Tools Illustration Tool Name Tool Number 73III Automotive Meter 105-R0057 or equivalent Vehicle Communication Module (VCM) and Integrated Diagnostic System (IDS) software with appropriate hardware, or equivalent scan tool Flex Probe Kit 105-R025C or equivalent

Scheme 26

Scheme 27

International Standards Organization (ISO) 9141 Communications Network

The ISO 9141 communications network is a single wire network. The ISO 9141 communications network does not permit intermodule communication. When the scan tool communicates to modules on the ISO 9141 communication network, the scan tool must request all information; the modules cannot initiate communications.

The following fault chart describes the specific ISO 9141 network failures and their resulting symptom

ISO 9141 NETWORK COMMUNICATION FAULT CHART

High Speed Controller Area Network (HS-CAN)

The HS-CAN uses an unshielded twisted pair cable of data (+) and data (-) circuits. The data (+) and the data (-) circuits are each regulated to approximately 2.5 volts during neutral or rested network traffic. As bus 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 bus message is sent. Multiple bus messages can be sent over the network CAN circuits allowing multiple modules to communicate with each other. The HS-CAN is a high speed communication network used for instrument cluster (IC), PCM, ABS module, restraints control module (RCM), and occupant classification system module (OCSM) communications, and designed for real time information transfer and control. The HS-CAN will not communicate while certain faults are present, but will operate with diminished performance with other faults present. The HS-CAN bus may remain operational when 1 of the 2 termination resistors are not present.

The following fault chart describes the specific HS-CAN failures and their resulting symptom

HS-CAN COMMUNICATION FAULT CHART

The following chart describes the specific HS-CAN messages broadcast by each module, and the module(s) that receive the message

HS-CAN MODULE COMMUNICATION MESSAGE CHART