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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,

[email protected],[email protected]

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: Bluetooth；OBD-II；CAN bus；MCU

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.


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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 world’s major automobile part manufacturers.


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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 realizing data sharing among multiple ECUs in a whole car. Meanwhile, J1939 Protocol supports fault diagnosis; and it can read or clear the diagnosis fault codes through diagnostic tools.

3. Systematic design

3.1. Hardware design

3.1.1. Peripheral circuit of the micro-controller

Figure3 is the peripheral circuit diagram of the micro-controller. The system uses 16-bit

XC2200-series micro-controller of Infineon. XC2200 series can provide flash memory ranging from 192KB to 832KB, optional EEPROM simulation, the SRAM which can reach a maximum of 82KB, and the CPU with maximum 100MHz clock frequency.

Infineon expands flash memory from 32KB to 1.6MB, increases RAM to 138KB, and improves clock frequency to 128MHz. Through a pin compatible MCU, product series can be expanded to meet higher performance requirement. To reach the requirement of software development independent from hardware in AUTOSAR standard program model, memory protection unit (MPU) is integrated in the controller. In addition, Infineon also provides separate FlexRay communication controller which can be easily added to the system [7].

Figure 3.Circuit diagram of the micro-controller

3.1.2. CAN communication interface module

Figure 4 shows the CAN communication interface circuit diagram in diagnosis system. Through this circuit, the data in the CAN bus of Auto OBDII interface can be read by the XC2200 series micro-controller of Infineon, and the data in the micro-controller can also be sent to the CAN bus of the automobile.


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Figure 4.Circuit diagram of CAN communication interface

3.1.3. Circuit of blue tooth interface

The blue tooth module adopted in this system is FBT06 series, the intelligent wireless data

transmission created by Modiate. The module uses Bluetooth2.1, with the advantages of of low cost, small size and high sensitivity of transcending, etc. It can support master/slave mode, hardware/software setting, wired/wireless double AT channels, PIO expansion and ADC sampling. The software supports as many as 37 AT commands and 9 active reporting instructions and the serial baud rates from 1200 to 1382400. Therefore, the serial port signal at the micro-controller can be converted into blue tooth signal via blue tooth module. Smart-phones with blue tooth function can receive the data transmitted via the blue tooth interface. The circuit of the blue tooth interface is as shown in Figure 5.

Figure 5.Circuit diagram of blue tooth interface module

3.2. Software design for CAN-Bluetooth module

The blue-tooth work of CAN-Bluetooth module is under slave mode while the blue-tooth work of

smart-phone or PAD display terminal is under master model. Serial data communication is adopted between CAN-Bluetooth module and smart-phone display terminal. The communication mode is N-8-1 format, with 1 start bit, 8 data bits, 1 stop bit, no verification, and 115200bps’s Baud rate.

3.2.1. Main functions of the application software at CAN-Bluetooth module

1) Convert the CAN message information from ECU into the data of serial format (including ID address of CAN) and send it to the display terminal (smart-phone). 2) Analyze the command from the display terminal according to the setting communication protocol (J1939 Protocol) and convert it into the data in the corresponding CAN message format.

3.2.2. Communication protocol for the application software of CAN-Bluetooth module

The information interaction between CAN-Bluetooth module and display terminal is carried out in

answer mode. Display terminal sends the touch button command, and CAN-Bluetooth module responses the corresponding command. When the touch button of the display terminal is triggered for the first time, the request shall be sent..After CAN-Bluetooth responses the request, i.e., the display terminal receives the feedback data, the data will be analyzed and displayed.Then the whole mission completed. When the display terminal finishes this command, another request command will be sent. It


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will wait for command response from the CAN-Bluetooth module, and so on. Until the last task is executed, thel touch button of the display terminal can be switched to other function request.

System ECU mainly adopts two communication methods: single frame communication and multiframe communication. Single frame is mainly adopted when monitoring the communication network of a whole car. The number of flexible fault codes is variable during diagnosis so that single and multiframe communication needs to be used in combination .

In the process of diagnosing fault, system ECU will send data frames of fault diagnosis, mainly including fault type, diagnostic trouble code (DTC), parameter group number (PGN) etc. The fault type is divided into two kinds: current fault (DMI) and previous fault (DM2).The diagnostic tools can diagnose the fault components in the system, convenient for the user to timely troubleshooting.Table 2 shows various data frames and parameter groups used for the communication protocols of system ECU.

3.3.Software design at display terminal (Smart-phone or PAD)

Figure 6 is the software flow chart of Smart-phone or PAD

Figure 6.Software flow chart

Display content:

1) Operation buttons and condition of the blue tooth devices; 2) System connection condition; 3) List and selection of the monitoring parameters, including engine speed, vehicle velocity,

coolant temperature, accelerator pedal state and load percentage under current rotate speed etc; 4) Fault code display and interpretation.


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4. Operation demonstration

Most of the Android smart-phones and pads in current market are equipped with blue tooth

interfaces. After installing the designed APP software on the smart-phones, we can use this software [8] to observe and read abundant parameters of automobile engines through the blue tooth interface. The specific reading methods are as follows: 1) Connect the detector to the OBDII diagnosis interface of the automobile, then start the car; 2) Turn on your smart-phone into wireless & network -> blue tooth setting -> select blue tooth, scan the equipment after accessing to the software, find the blue tooth equipment, and select corresponding equipment to match it; 3) After executing the above steps correctly, your smart-phone and the detector shall be connected via blue tooth interface. You can observe the abundant data about automobile state transmitted via OBDII diagnosis interface and carry out real-time monitoring.

5. Conclusions

This paper elaborates the OBD-II electric control fault diagnostics system for automobiles based on

blue tooth. This diagnostics can realize fault diagnosis for the electric control units of OBD-II standard automobiles, e.g. electric control unit of engine etc. Using Infineon chip as the core, combined with the detector made by appropriate peripheral circuit, the diagnosis information of the automobile self-diagnosis system can be transmitted to smart-phones on a real-time basis. Compared with those current specialized detectors , this detector has obvious advantages. Current diagnostics has shortcomings such as complicated structure, high costs, being inconvenient to take with and low diagnosis efficiency etc. And diagnosis system in this paper has advantages such as inexpensive, small, convenient to use and with wide market prospect.

The development of automobile fault diagnostics meet the needs of the auto repair plants that one diagnostic equipment support multi-vehicle diagnosis.They don’t have to purchase expensive specialized diagnosis devices for each type of vehicle respectively, thus significantly reducing the costs of the auto repair plants. In addition, this detector helps maintainers to work efficiently because it is easy to use.

6. References:

[1] YanFuwu，“Remote Vehicle Diagnostics System Based on Smart-phone”，Journal of Huazhong

University of Science and Technology，vol.11，No.1，pp.125-128，2012. [2] RoyS.Cox，“Introduction to OBD II”，Machine Press，China，2006. [3] Yang,Yalian,Chen,Baolin,Su,Lin，“Research and Development of Hybrid Electric Vehicles

CAN-Bus Data Monitor and Diagnostic System through OBD-II and Android-Based Smart-phones”，6th International Conference on Computer Sciences and Convergence Information Technology (ICCIT) ，pp.13-22，2013.

[4] XieKungen，“The Design and Implementation of Automotive Diagnostics Based on OBD II Standard”，Harbin Institute of Technology，vol.4，No.1，pp.32-35，2009.

[5] ZhangFangWei，“The research of Bluetooth diagnostic system”，Vehicle Electrical，vol.7，No.1，pp.9-12，2011.

[6] Yun,Hyun-Jeong,Lee,Shin-Kyung, Kwon,Oh-Cheoni，“Vehicle-generated Data Exchange Protocol for Remote OBD Inspection and Maintenance”，6th International Conference on Computer Sciences and Convergence Information Technology (ICCIT) ，pp.81-84，2012.

[7] HuangWeidong,Zhang Yue, Liu Junhong，“Research and design of the automobile OBD data state monitoring system based on the Android phones”，Advanced Materials Research，vol.1，No.1，pp.2301-2305，2013.

[8] LiJiaowen，“Bluetooth Mini OBD Automobile Information Detector Based on TL718”， Information Technology，vol.9，No.1，pp.277-279，2013.


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