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System of onboard self-diagnostics (OBD) - General Information

general description

The aim of any on-board self-diagnostics system (OBD) is to detect faults and malfunctions under control systems to be entered in the memory of the processor corresponding diagnostic trouble codes (DTC), and alert the driver of the fact of violation (usually by mounted in a combination of devices the control lamp of refusals MIL / <Check motor>) .

Apart from the DTC in the ECM memory is fixed as the current operating parameters of the engine at the time of violation.

At infringement of serviceability of functioning of information sensors involved in the process of motor control, ECM systems can produce switching to emergency mode. This activates the basic operating parameters to ensure adequate operation of the engine (an absolute psevdosignal faulty sensor is simulated directly by the control module), but with the inevitable reduction in the efficiency of its impact and increase fuel consumption - the car should be driven away on a car repair shop in order to identify and eliminate the causes of failure.

The composition of the OBD system includes several diagnostic devices making monitoring of separate parametres of systems of decrease in toxicity and fixing revealed refusals in memory of the onboard processor in the form of individual codes of malfunctions. The system also produces verification of sensors and actuators, controls the operating cycles of the vehicle makes it possible to freeze the parameters and purification of the memory block.

Considered in this manual models come with on-board diagnostics of the second generation of the standard SAE (OBD II). The main element of any OBD system is an onboard processor, more often referred to as electronic control module (ECM). ECM is the brain of the engine management system. The raw data signals and for the failures and disturbances OBD module receives information from various sensors and other electronic components (circuit breakers, relays, etc.). Codes stored faults recorded in the memory of the processor.

Control Module diesel models includes an option for self-feedback, allowing to minimize the effect of errors of the main hardware input and output paths ECM.

The principle of self-organization function ECM on diesel models

Reading the data processor memory OBD made using a special scanner (such as HI-Scan), connected to the 20-pin diagnostic socket reader Database (DLC), fixed to the body of the air cleaner in the left rear corner of the engine compartment - another standard 16-pin DLC OBD II is installed in the car to the left under the dashboard.

The DLC allow reading fault codes with a special scanner

1 - Ground 2 - Signal Ground 3 - The function of on-board diagnostics 4 - Battery voltage (V)

On the service components of engine management systems / emission control are subject to special warranty with extended validity period. Do not attempt to self-diagnose ECM failure or replacement of system components before the release dates of these obligations, - address to experts branded service stations of the company KIA.

Data on diagnostic devices

Check of serviceability of functioning of the system components of the engine and emission control can be performed with a universal digital meter (DMM). Using a digital meter is preferred for several reasons. First, on analogue devices it is rather difficult (sometimes impossible) to determine the result of readings with an accuracy of hundredths and thousandths of, while at inspection of the contours including in the structure electronic components, such accuracy takes on special significance. The second, no less important reason is the fact that the internal contour of a digital multimeter, has high enough impedance (internal resistance of the device is 10 megohms). As the voltmeter is connected to a checked chain in parallel, accuracy of measurement is higher, the smaller parasitic current will flow through the device itself. This factor is not significant when measuring relatively high voltages (9 ÷ 12), but becomes the determining the diagnosis of issuing low voltage components, such as, for example, lambda probe, which refers to the measurement of a volt.

Using the diagnosis of the systems under consideration DMM high impedance significantly increases the accuracy of measurements made in the low voltage range.

Parallel monitoring of parameters of signals, resistance and voltage in all control circuits can be made using a splitter connected in series to the terminal control module (ECM). Measurement of signal parameters at the terminals of the splitter in various modes of operation of the engine makes it possible to determine the current state of the latter taking place and to identify violations.

In the diagnosis of electronic control systems for engine, transmission, ABS and SRS using special scanners standard SAE (GST), which include scanner HI-Scan. Many scanners SAE the second generation (OBD II) are multifunctional due to the possibility of installing replacement cartridges depending on the model of the diagnosed car (Ford, GM, Chrysler, etc.), while others are linked to the requirements of regional authorities and are intended for use in certain areas of the world (Europe, Asia, USA and so on). Connection is made to the on-board scanner DLC.

An alternative way to read data is OBD connection to a personal computer equipped with a special cable and software equipped with OBD.

Universal Adapter K-L-Line is used for signal conditioning RS-232 port and interfaces ISO-9141 (K-Line) and ALDL. By adapter connectors can connect a variety of cables to allow for reading data from the OBD cars of different brands. Provided on the adapter switches and indicators let you select the appropriate modes of operation and about the operation to assess the quality of output lines. Thus, the green LED labeled L-Line indicates the connection line L with the weight of the car. Enabling the red LED labeled K-Line confirming the presence on the line K in the current time of high capacity. When communicating with the OBD system of a vehicle blinking can be imperceptibly due to the high speed data exchange. Connecting to a computer directly to the 25-pin COM port or 9-pin COM port via adapter cable RS232 25-9.

Universal adapter KL-Line.

Some readers in addition to the routine diagnostic operation allows connecting to a PC to make printing out stored in the control module concepts different equipment (if incorporated in the ECM), to program the anti-theft system and controls the various devices of the car, as well as real-time monitoring of signals in electric Car chains.

Read the DTC

For more information on reading fault codes, refer to the user guide to the scanner. List of fault codes is given in Specifications to the Head of the Power supply system, motor control / emission control and exhaust.

Cleaning system memory self-test

Alternatively, purification of memory OBD II processor can be made using a scanner connected to the DLC.

Connecting the PC to the onboard system of self-diagnostics OBD II through the interface controller BR16F84-1.0 protocols standard SAE (PWM and VPW) and ISO 9141-2

The controller is not designed to connect to the onboard systems of the first generation of self-diagnosis (OBD I)!

Standard VPW responsible production model of GM, PWM - Ford, ISO 9141-2 - Asian and European models.

Overview

Scheme of the PC connection to the DLC-board self-diagnostic system OBD II by the controller BR16F84-1.0

The subject device is a microcontroller configured for CMOS technology (CMOS). The device acts as a simple scanner is used to read diagnostic trouble codes and data systems OBD II (engine speed, coolant temperature and intake air load characteristics, the flow of air entering the engine, etc.) within the SAE J1979 specification via the bus all performance (PWM, VPW and ISO 9141-2).

The main purpose

To connect to a computer is sufficient 3-core wire connected to the diagnostic connector made 6-wire cable. The supply voltage is supplied to the controller via a 16-pin diagnostic connector OBD.

Recommended Use

To connect the device to the car can be used unshielded cable is no longer than 1.2 m, which is of particular importance when using the protocol PWM. When using long cables, reduce the resistor at the input device (R8 and R9 or R15). When using a shielded cable, the screen should be turned off to reduce capacity.

The cable for connection to a PC serial port can also be unshielded. The device operates with a stable cable lengths up to 9 m. At much longer cable lengths, use a more powerful RS-232 device.

The topology of the electrical connections is arbitrary. When humidity apply additional shunt capacitors.

General principles of data sharing

If not otherwise stated, all numbers are given in hexadecimal format 16 (hex), - a decimal format are labeled dec.

Data exchange is on the three-wire serial connection without initialization sharing service messages (handshaking). The device listens to the channel for messages, carries out the received command and sends the results to a personal computer (PC), and then immediately returns to listening mode. Incoming and outgoing controller of a data arranged in a series string of consecutive bytes, the first of which is a control. Typically, the control byte is a number from 0 to 15 dec (in decimal notation) (or 0-F hex), the following description describes the number of data bytes. For example, 3-byte command is as follows: 03 (check byte) 1st byte 2nd byte 3rd byte. This format is used for entering commands to the survey on-board self-diagnostic system, and outbound messages containing the requested information. Note that in the control byte are used only four lower bits, - the upper bits are reserved for some special commands may be used when initializing PC connected to the controller and negotiating a data transfer protocol, and a controller for control of transmission errors. In particular, in case of transmission errors, the controller unit produces the most significant bit (MSB) of control byte unit. If successful transfer all four bits are set to zero.

There are some exceptions to the rules of use of the control byte.

Initialize the controller and on-board self-diagnostic system

To begin data exchange PC must make a connection with the controller, the controller then initialized and the data channel OBD II.

Making a connection

After connecting the controller to the PC and the OBD diagnostic must be made of its initialization to prevent <hang> related to noise in successive lines if their connection was made to turn on the power controller. It also provides simple verification interface activity. The first signal is sent byte 20 hex, the controller perceived as a team to establish the connection. In response, the controller sends a control instead of a single byte FF hex (255 dec) and goes into standby mode reception. Now PC may transition to the initialization data channel.

This case is one of the few where the controller uses the control byte.

Initialization

At this stage, the initialization protocol, which will be exchanged, and in the case of protocol ISO - initialization of the onboard system. The data exchange is carried out by one of three protocols: VPW (General Motors), PWM (Ford) and ISO 9141-02 (Asian / European manufacturers).

There are many exceptions: for example, in the survey of some models of Mazda vehicles can be used <Ford> protocol PWM. Thus, if transmission problems occur should first try to use any other protocol. Protocol selection by transmission combination consisting of the control byte 41 hex, and immediately following the byte defining the protocol type: 0 = VPW, PWM = 1, 2 = ISO 9141. Thus, for example, team 41 02 hex initialization protocol ISO 9141 .

In response, the controller sends a control byte and the status byte. Setting MSB control byte indicates the presence of problems, while following it the status byte will contain the relevant information. Upon successful initialization is sent to the control byte 01 hex, indicating that what follows is the verification status byte. In the case of reports VPW and PWM verification byte is a simple echo determines the protocol bytes (0 and 1, respectively), during initialization ISO protocol 9141 this will be a digital key returned by onboard processor OBD and determines which of the two slightly differing versions Protocol to be used.

Digital key has a purely informational purpose. It should be noted that the initialization protocol VPW and PWM occurs much faster because it requires only the transfer of relevant information to the controller. On models that meet the standard of ISO, initialization takes about 5 seconds spent on information exchange controller with on-board processor, produced at a rate of 5 bps. Attention is drawn to the reader that on some models of cars of family ISO 9141 initialization protocol is suspended, if the request for the issuance of the data will not be transferred over a 5-second interval - this indicates that the PC should make automatic issue queries every few seconds, even in idle mode.

Once the connection and initialization protocol begins regular exchange of data, consisting of coming from the PC requests and responses issued by the controller.

The procedure for data exchange

The operation of the controller by using a family of protocols ISO 9141-2 and SAE (VPW and PWM) occurs on several different scenarios.

Exchange under reports SAE (VPW and PWM)

If the data exchange takes place according to the protocol buffering only one frame of data that is subject to the need to define the seizure or return of the frame. In some (rare) cases, on-board processor can transmit packets, consisting of more than one frame. In this situation, the request must be repeated until all frames until the packet will be accepted.

Request always formed as follows: [Control byte] [Request standard SAE], [block number]. As mentioned above, the control byte is normally a number equal to the total number of bytes following it. The request is made in accordance with the specification SAE J1950 and J1979 and consists of a header (3 bytes), a sequence of information bytes and byte error control (CRC). ?�?�???�?�????, ?�?�?? ?? ?�?? ?????�???? ???�?? ?????�???????�?�???? ???? ?�?�?????????? ?�?????????????�?�???? ?? ???�?????????? ???????�???�?�???�?????? ???? ?????�?�???�?????�?�???????? SAE, ?????�???�?�???�?�?�?�?? ???????�?????�?????????? ?�?�???�?� ?? ???????�???� ???�?????� ?????�???�?�???? ?????�?�???�?�???????�?? ???????�?????�?�?�??.

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• ?�???�?�???�?�???� ?????????�???�???� ???????�???????�?� ISO 14230.

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