Automotive Computer Network Repair

Book excerpt: Automotive Computer Network Repair (Diagnostic Strategies of Modern Automotive Systems) By Mandy Concepcion In this book we will cover the intricacies of automotive inter-module communication systems or networks. The scope of this section will also go beyond the normal needs of an automotive technician. Hence, this will probably be the most difficult part of this series to comprehend. Be patient and open minded. Always give yourself time to absorb the knowledge and do not be discouraged. Special emphasis will be placed on the CAN system (Controller Area Network), since it is now the standard. CAN is one of the 9 OBD-2 protocols. A protocol is an agreement on communications interchange. It is in essence a computer communication language and specifies signaling, wiring, size of cables used, who controls the network and voltage levels. Various protocols were used in the past, some proprietary and some generic such as ISO 9141 and SAE 1850 VPW, but the standard is now the CAN protocol. Virtually all vehicle networks now talk to each other though the CAN protocol. It is now common place to see the seat belt, SRS-Airbag, transmission, ABS-Brakes, engine and radio modules or computer talking to each other through the network. Ever wondered why your radio volume goes up when you accelerate the vehicle? That's the engine computer or module telling the radio to raise the volume due to a higher RPM and hence higher ambient noise. It is also common to see a non-shifting transmission due to a faulty network and the issue not being related to the transmission at all. Hopefully this book will shed some light on the operation and knowledge needed to tackle automotive networks in today's vehicles...... Enjoy. Table of Contents 1. INTRODUCTION * - Automotive inter-module communication systems or networks * - Asian, Domestics and European Vehicles * - Fully Networked vehicles. 2. THE NEED FOR IN-VEHICLE NETWORKING * - Use of electrical and electronic components * - Networked automotive sensors. * - Sharing of sensor information * - Weight savings and the simpler wiring harnesses * - Networking and modular systems 3. THE NEED FOR PROTOCOLS * - CAN or Controller Area Network communication protocol * - CLASS A - Low speed * - CLASS B - Medium speed * - CLASS C - High speed * - SAE (Society of Automotive Engineers) * - ISO (International Standards Organization) * - What is a Gateway? 4. NETWORKING ESSENTIALS * - the 7-layer ISO/OSI reference model * - PHYSICAL LAYER * - DATA LINK LAYER * - APPLICATION LAYER * - Medium Access * - CARRIER SENSE MULTIPLE ACCESS or CSMA * - Network latency * - The Topology of a network * - The STAR topology * - The BUS topology * - The TREE topology * - The RING topology 5. DIFFERENT COMMUNICATION NETWORK * - The CCD data bus (Chrysler Collision Detection) * - CCD bus ground * - CCD bus bias voltage * - OEM scan tool (DRB III) * - NO TERMINATION message fault * - The PCI bus (Programmable Communications Interface) * - A CSMA/CD media access scheme * - The Header, DATA, CRC, IFR and EOF elements * - DCL (Data Communications Link) * - circuit 914 and 915 * - SCP (J1850) (Standard Corporate Protocol) * - Dual wire twisted pair bus topology * - The ISO 9141 protocol * - The NGS "DATA LINK DIAGNOSTICS" menu option * - GM (Data Line) UART Serial Communications * - UART data line communications * - GM CLASS 2 data bus * - State of health messages * - The Tech-2 scanner has a dynamic menu configuration * - The Tech-2's PING-ALL-MODULES 6. CAN (Controller Area Network) * - implementation of the CAN protocol * - 11 bit and 29 bit identifyer * - EPA approved for MY 2003 and up * - CAN A, B and C * - MID and PID CAN identifyers * - Master time-keeper-node * - Drive-by-wire systems * - Byteflight, Flexray, and Time-triggered CAN or TTCAN * - The CAN Data-Frame * - The CAN bus-access arbitration * - SOF (start-of-frame) bit * - Control bit * - Arbitration bits * - Data bits * - EOF or end of frame bit