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  • OBD-II Electric Control Fault Diagnostics for Automobiles Based on Bluetooth

    Yongqing Ji, YuanMing Gong

    School of Automotive Engineering, Shanghai University of Engineering Science, Shanghai,China,

    349511301@qq.com,gongyuanming@tsinghua.org.cn

    Abstract Against the background of insufficient handheld automobile fault diagnosis apparatuses, a wireless

    automobile fault diagnostics based on Bluetooth technology is constructed by combining Bluetooth, CAN (Controller Area Network) bus and smart-phone to monitor and diagnose automobile faults on line. This paper elaborates the technical scheme, system structure, communication protocols and realizing circuits for software and hardware of the construction. This system can cater to the real-time and mobility demand of automobile diagnosis technology.

    Keywords: BluetoothOBD-IICAN busMCU

    1. Introduction

    With the rapid development of automobile electronic control technology and the continuous

    increasing of various on-board electronic control units and equipment, automobile fault diagnostics are also becoming increasingly complicated. Traditional diagnostics has shortcomings such as complicated structure, high costs, being inconvenient to take with and low diagnosis efficiency etc. Currently, the most widely used diagnostics is the Second On-Board Diagnostics (OBD-II)[1]. This system adopts a wireless fault diagnostics for automobile engines based on blue tooth technology and on-board self-diagnostics. Featured by simply designed hardware, low difficulty in software development, easy remote interaction, and the capability of effectively overcoming regional discrepancies, this system can cater to the real-time and mobility demand of automobiles [2].

    2. Conceptual design

    2.1. Schematic diagram

    The operating principle of OBD-II electric control fault diagnostics for automobiles based on blue

    tooth is shown in Figure 1.

    Figure 1.Principles of electric control fault diagnostics

    CAN-Bluetooth module in the electric control fault diagnostics communicates with the automobile

    electronic control unit (ECU) via OBD interface (CAN bus) to read the information from ECU. Then the information shall be converted into blue tooth data and sent to a smart-phone with blue tooth function. Similarly, the smart-phone can also send the data information to CAN-Bluetooth module

    OBD-II Electric Control Fault Diagnostics for Automobiles Based on Bluetooth Yongqing Ji, YuanMing Gong

    International Journal of Digital Content Technology and its Applications(JDCTA) Volume8, Number4, August 2014

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  • which converts the data into CAN message information before sending to ECU. Therefore, wireless interactive communication shall be realized between the smart-phone and ECU information, and the information on ECU can be read [3].

    2.2. Introduction to OBD-II and the definitions of its interfaces

    OBD-II fault diagnosis standard is the standard to develop the second generation of fault

    self-diagnostics [4]. This standard is widely supported by major automobile manufacturers in the world. This kind of ECUs are capable to monitor engine control system and exhaust system. When a system failure occurs, the corresponding fault code will be generated. The fault codes can be acquired from ECU via certain programs; therefore, the nature and location of fault can be determined accurately. In addition, a wide range of monitoring systems has been added, which makes it possible to carry out real-time monitoring on the working conditions of automobiles. OBD-II system requests to monitor any part or system related to exhaust, with the focus on monitoring the faults in fuel and air measuring system, ignition system, engine flameout and auxiliary device for exhaust gas control. The OBD-II system monitors the auto parts and system failure on a real-time basis, so that the exhaust of automobiles will not exceed the requirement of regulations in its service life. The definition of OBD interface is shown in figure 2.

    Figure 2.Definitions of the OBD interface terminals (16pin female terminal)

    2.3. Bluetooth technology

    Bluetooth is a kind of technology jointly declared by five famous companies in the world in May, 1998, including Ericsson, Nokia, Toshiba, International Business Machines and Intel. Its substantial content is to establish universal wireless interface and the open standard for the software controlled by them, so as to further integrate communication and computer, which enables the portable devices manufactured by different manufacturers to have the performance of mutual usage and mutual operation in a close range without being connected by wires.

    Bluetooth technology is a new kind of short distance wireless communication protocol and a kind of open standard for wireless data and voice communication, which can replace the existing wireless wired interface [5].

    Bluetooth technology has the following advantages: a. Strong portability. It can be applied to a variety of communication situations; b. Simple hardware integration application, low cost, easy to implement and promote; c. Low power consumption, and less harmful to the human body; d. With spread spectrum and frequency-hopping technology, it has strong anti-jamming capability and increases the safety of information transmission. Combination of automobile system and blue tooth system will will bring greater convenience to the

    automotive production and service. If it is further connected with smart-phones, the car owners can know the conditions of their cars anywhere at any time, and carry out necessary control.

    OBD-II Electric Control Fault Diagnostics for Automobiles Based on Bluetooth Yongqing Ji, YuanMing Gong

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  • 2.4. Communication modes for each part

    CAN-Bluetooth module and ECU can realize bidirectional communications via CAN bus, so that we are able to read real-time data information from ECU directly.

    2.4.1. Data information from ECU on CAN-Bluetooth module

    The data information from ECU is data message in CAN format. CAN-Bluetooth module reads the

    data frame of CAN format and the corresponding CAN ID address.

    2.4.2. Data information sent to ECU by CAN-Bluetooth module

    The data information sent to ECU by CAN-Bluetooth module comes from the command of smart-phone keyboard (for instance, Reading DTC code and reading working parameters etc.). The communication is realized via wireless blue tooth signal. Data analysis shall be carried out on the command from smart-phone keyboard via the application software of CAN-Bluetooth module in line with the set communication protocols (J1939 Protocol and ISO15765 Protocol), which can convert the data into the data frame in corresponding CAN format and send it to ECU.

    2.4.3. Data sent to smart-phone terminal by CAN-Bluetooth module

    CAN-Bluetooth module and smart-phone conduct wireless RF communication via blue tooth

    interface module. The received CAN- message- format ECU data shall be converted into corresponding serial data (including the ID address of CAN) by CAN-Bluetooth module, and then sent to smart-phone.

    According to the set communication protocols (J1939 Protocol and ISO15765 Protocol etc.), we parse the data through the application software of mobile phone terminal and display the data from ECU.

    2.4.4. Data at smart-phone terminal received by CAN-Bluetooth module

    The data received by CAN-Bluetooth module from smart-phone terminal, i.e., command request (in

    blue tooth message format) shall be analyzed in line with the set communication protocols (J1939 Protocol and ISO15765 etc.), converted into the data in corresponding message format, and sent to ECU [6].

    2.5. J1939 communication protocol

    J1939 Protocol is released by Society of Automotive Engineers. It is a network protocol based on

    CAN bus and supports high speed communication closed-loop control between multiple ECU, mainly applied to vans and passenger cars. There are some differences between this specifications and CAN specifications. For instance, in message routing section, CAN specifications define not to use node address, while node address is a must in this specifications for the purpose of preventing the situation that multiple nodes use one identifier. Meanwhile, J1939 Protocol redefines arbitration field. It is a CAN-based upper layer protocol involving in application layer; and it makes clear rules about the address configuration, naming, communication method of the ECU inside automobiles as well as message sending priority, data length and parameter range etc.; in addition, it explains in detail the communication contents of each specific ECU inside the automobiles. J1939 Protocol gives full play to the excellent performance of CAN to a greater extent, which establishes high speed data transmission network based on CAN bus for each on-board electronic control unit, and realizes data sharing among on-board electronic control units, thus effectively reducing the quantity of electronic wires. This is conducive to improving the flexibility, maintainability and stability of electronic control units of the automobiles. So far, SAE J1939 has become an important communication standard supported by all worlds major automobile part manufacturers.

    OBD-II Electric Control Fault Diagnostics for Automobiles Based on Bluetooth Yongqing Ji, YuanMing Gong

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  • The J1939 Protocol in this electric control system adopts CAN2.0B extended frame format in CAN specifications, with the Baud rate of 250kbps. ECU based on CAN communication of J1939 Protocol can provide engine performance monitoring parameters and vehicle network communication, thus r

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