System of onboard self-diagnostics (OBD) - the general information

The general description

Problem of any onboard system of self-diagnostics (OBD) is revealing of refusals and infringements of functioning of under control systems with entering in memory of the processor of corresponding diagnostic codes (DTC) and the notification of the driver about the infringement fact (usually by means of built in in a combination of devices of a control lamp of refusals MIL / Check up the engine).

Besides code DTC in memory ECM it is fixed also current working parametres of the engine at the moment of infringement revealing.

At infringement of serviceability of functioning of the information gauges which are taking part in managerial process by the engine, ECM can make switching of systems in emergency operation. The base working parametres providing adequate work of the engine are thus activated (some absolute pseudo-signal of the faulty gauge is feigned directly by the management module), however with inevitable decrease in efficiency of its return and increase in the expense of fuel, - the car should be driven away on a car repair shop for the purpose of revealing and elimination of causes of a failure.

System OBD structure includes some the diagnostic devices making monitoring of separate parametres of systems of decrease of toxicity and fixing revealed refusals in memory of the onboard processor in the form of individual codes of malfunctions. The system makes also check of gauges and actuation mechanisms, supervises operational cycles of a vehicle, provides possibility of freezing of parametres and clearing of the block of memory.

Models considered in the present Management are completed by system of onboard diagnostics of the second generation of standard SAE (OBD II). The Basic element of any system OBD is the onboard processor, more often named the electronic module of management (ECM). ECM is a brain of a control system of the engine. The initial data, and also signals registered OBD refusals and infringements arrive on the module from various information gauges and other electronic components (switches, the relay etc.). Codes of the registered malfunctions are fixed in memory of the processor.

In modules of management of diesel models function of self-diagnostics with a feedback is provided, allowing to minimise effect of errors of the main equipment of entrance and target paths ECM.

Principle of the organisation of function of self-diagnostics ECM on diesel models

Data read-out of memory of processor OBD is made by means of the special scanner (type HI-Scan), reading of a database connected to a 20-contact diagnostic socket (DLC), fixed on the air cleaner case in the left back corner of an impellent compartment, - one more standard 16-contact DLC OBD II is established in car salon at the left under the panel of devices.

Diagnostic sockets DLC allow to make reading of codes of malfunctions by means of the special scanner

On service of components of control systems by the engine/decrease of toxicity of the fulfilled gases special guarantee certificates with the prolonged period of validity extend. It is not necessary to undertake attempts of independent performance of problem diagnostics ECM or replacement of components of system, to an exit of terms of the given obligations, - address to experts of firm car repair shops of company KIA.

Data on diagnostic devices

Check of serviceability of functioning of components of control systems by the engine and decrease in toxicity of the fulfilled gases can be made by means of a universal digital measuring instrument (multimeter). Use of a digital measuring instrument preferably for the several reasons. First, on analogue devices it is difficult enough (at times, it is impossible), to define result of the indication to within the 100-th and thousand shares while at inspection of the contours including in the structure electronic components, such accuracy takes on special significance. The second, the reason that fact is not less important that the internal contour of a digital multimeter, has high enough impedance (internal resistance of the device makes 10 МОм). As the voltmeter is connected to a checked chain in parallel, accuracy of measurement by that above, than the smaller parasitic current will pass through actually device. The given factor is not essential at measurement concerning high values of pressure (9 12), however there is defining at diagnostics of elements giving out low-voltage signals, such, as, for example, a ljambda-probe where it is a question of measurement of shares of volt.

Parallel monitoring of parametres of signals, resistance and pressure in all chains of management can be made by means of a splitter connected consistently to a socket of the module of management (ECM). Measurement of parametres of signals on splitter plugs in various modes of functioning of the engine allows to define a current condition of the last and to reveal taking place infringements.

At diagnostics of electronic control systems by the engine, transmission, ABS and SRS special scanners of standard SAE (GST) which number scanner HI-Scan concerns also are applied. Many scanners SAE of the second generation (OBD II) are multipurpose at the expense of possibility of installation of replaceable cartridges depending on model of the diagnosed car (Ford, GM, Chrysler, etc.), others are adhered to requirements of the regional authorities and are intended for use in certain areas of the world (Europe, Asia, the USA etc.). Scanner connection is made to onboard DLC.

Alternative way of data read-out OBD is connection to system of the personal computer equipped with a special cable and equipped with software OBD.

Universal adapter K-L-Line (www.autoelectric.ru) serves for the coordination of signals of port RS-232 and interfaces ISO-9141 (K-Line) and ALDL. The various cables can be connected To adapter sockets, allowing to make data read-out OBD from cars of various marks. The switches provided on the adapter and indication elements allow to choose necessary operating modes and approximately to estimate quality of functioning of target lines. So, the luminescence of a green light-emitting diode with marks L-Line testifies to connection of line L with weight of the car. Activation of a red light-emitting diode with marks К-Line confirms about presence on a line To in a present situation of time of high potential. At the established communication with system OBD of the car the blinking of indicators can be imperceptible for an eye in view of high speed of data exchange. Connection to the computer is made directly in a 25-contact CATFISH-PORT or in a 9-contact CATFISH-PORT by means of transitive cable RS232 25-9.

Some input readers besides usual diagnostic operations allow at connection to the personal computer to make распечатывание stored in memory of the module of management of basic schemes of the various equipment (if those are put in ECM), to program anticreeping system and blocks of management of various devices of the car, and also in real time to observe signals in electric chains of the car.

Reading of codes DTC

Clearing of memory of system of self-diagnostics

Connection of the personal computer to onboard system of self-diagnostics OBD II by means of the interface controller BR16F84-1.0 under reports of standards SAE (PWM and VPW) and ISO 9141-2

The general data

The scheme of the organisation of connection PC to diagnostic socket DLC of onboard system of self-diagnostics OBD II by means of controller BR16F84-1.0

The considered device represents the microcontroller executed on technology КМОП (CMOS). The device plays a role of the elementary scanner and is intended for reading of diagnostic codes and the data of system OBD II (engine turns, temperature of a cooling liquid and soaked up air, loading characteristics, the expense of air arriving in the engine, etc.) within the limits of specification J1979 of standard SAE through the tyre of any execution (PWM, VPW and ISO 9141-2).

Main destination

To the computer it is enough for connection 3-zhilnogo a wire, connection to a diagnostic socket is carried out 6-zhilnym by a wire. Pressure of a food moves on the controller through 16-contact diagnostic socket OBD.

Recommendations about application

For device connection to the car than 1.2 m that has special value at use of report PWM can be used неэкранированный a cable, length no more. At cable use большей lengths it is necessary to reduce resistance of resistors on a device input (R8 and R9 or R15). At use экранированного a cable, the screen should be disconnected for the purpose of capacity decrease.

The cable for connection to a computer serial port also can be неэкранированным. The device stably works with a cable in length to 9 m. At much большей to length of a cable it is necessary to use more powerful коммуникатор RS 232.

The topology of electric connections is any. At the raised humidity apply additional shunting condensers.

The general principles of data exchange

Data exchange goes on three-wire consecutive connection without application инициализационного an exchange of office messages (handshaking). The device listens to the channel on presence of messages, executes accepted commands and transfers results to the personal computer (PC) then immediately comes back in a listening mode. Entering into the controller and the data starting with it are organised in the form of a chain of bytes consistently going one after another, first of which is control. Usually control byte represents number from 0 to 15 dec (in decimal calculation) (or 0-F hex), describing quantity of information bytes following further. So, for example, 3-bajtnaja the command will look as follows: 03 (control byte), 1st byte, 2nd byte, 3rd byte. The similar format is used as for entering commands on interrogation of onboard system of self-diagnostics, and for the outgoing messages containing the requested information. It is necessary to notice that in control byte four younger bits are used only, - the senior bits are reserved under some special commands and can be used PC at initialization of connection with the controller and the coordination of the report of data transmission, and also the controller for the control of errors of transfer. In particular, in case of an error by transfer, the controller makes installation of the senior meaning bit (MSB) control byte in unit. By successful transfer all four senior bits are established in a zero.

Initialization of the controller and onboard system of self-diagnostics

To start data exchange PC should make installation of connection with the controller, then initialize the controller and the channel of data OBD II.

Connection installation

After controller connection to PC and to diagnostic socket OBD its initialization for the purpose of prevention of the "lags" connected with noise in consecutive lines in a case if their connection should be made has been made before inclusion of a food of the controller. The elementary check of activity of the interface is simultaneously made. First of all the one-byte signal 20 hex, perceived by the controller as a command on connection installation is sent. In the answer the controller instead of the control sends unique byte FF hex (255 dec) and passes in a mode of expectation of reception of the data. Now PC can pass to initialization of the channel of the data.

Initialization

At the given stage report initialization on which data exchange will be made, and in case of report ISO – initialization of onboard system is made. Data exchange is made on one of three reports: VPW (General Motors), PWM (Ford) and ISO 9141-02 (the Asian/European manufacturers).

In the answer the controller sends control byte and condition byte. Installation MSB of control byte speaks about presence of the problems, the byte of a condition thus following it will contain the corresponding information. At successful initialization the control byte 01 hex, specifying that follows further верификационный condition byte is sent. In case of reports VPW and PWM верификационный the byte represents a simple echo of byte defining the report (0 or 1, accordingly), at initialization of report ISO 9141 it will be the digital key returned by onboard processor OBD and defining which of two versions of the report slightly different from each other will be used.

After installation of connection and report initialization the regular data exchange, consisting of arriving from PC inquiries and answers given out by the controller begins.

Data exchange order

Controller functioning at use of reports of family ISO 9141-2 and SAE (VPW and PWM) occurs under a little various scenarios.

Exchange under reports SAE (VPW and PWM)

At data exchange under the given reports there is a buffering only one shot of the data that means necessity of a concrete definition subject to capture or shot return. In some (rare) cases the onboard processor can transfer the packages consisting more than from one shot. In such situation the inquiry should repeat until all shots of a package will not be accepted.

The inquiry always is formed as follows: [Control byte], [Inquiry under standard SAE], [shot Number]. As already it was mentioned above, the control byte usually represents the number equal to full quantity of bytes following it. The inquiry is made out according to Specifications SAE J1950 and J1979 and consists of heading (3 bytes), sequence of information bytes and byte of the control of an error (CRC). We will notice that while the information on demand is formed in strict conformity with Specifications SAE, the consumer of control byte and shot number is the interface controller.

At successful end of procedure the reciprocal message always has the following format: [Control byte], [the Answer under standard SAE]. The control byte, as well as earlier, defines quantity of information bytes following it. The answer according to requirements of standard SAE consists of heading (3 bytes), a chain of information bytes and byte CRC.

At failure it is sent 2-bajtnoe the reciprocal message: [Control byte], [condition Byte]. Thus in control byte installation MSB is made. Four younger bits form number 001, testifying that the control is followed by unique byte, - condition byte. The given situation can arise often enough as Specifications suppose possibility of a lack of distribution the onboard processor of the data, and also transfer of the incorrect data to a case when the inquiry does not correspond supported by manufacturers of the car to the standard. The situation when the required data is absent in operative memory of the processor in time present situation is possible also. When the controller does not receive the expected answer, or obtains the damaged data, installation MSB of control byte is made, and after the control the condition byte stands out.

At collisions in the tyre the interface develops unique byte 40 hex, being in control byte with the nulled younger bit. The similar situation can arise often enough at loading of an automobile tyre by messages of higher than at the diagnostic data of a priority, - the computer should repeat initial inquiry.

Exchange under reports ISO 9141-2

Standard ISO 9141-2 is used by the majority of the Asian and European manufacturers of automobile technics. The structure formed PC inquiry a little than differs from used in standards SAE, with that only a difference that the controller does not require the information on number of a shot and corresponding given to be present at a package should not. Thus, the inquiry always consists of control byte and a chain of the information bytes including the control sum following it. As the reciprocal message the controller simply relays the signals generated by the onboard processor. The control byte in the reciprocal message is absent, therefore PC perceives the arriving information a continuous stream until the chain does not interrupt a pause in 55 milliseconds, informing on end of an information package. Thus, the reciprocal message can consist of one or more shots according to requirements of specifications SAE J1979. The controller does not make the analysis of shots, does not reject not diagnostic shots etc. PC should make own forces processing of the arriving data for the purpose of exarticulation of separate shots by the analysis of heading bytes.

The updatings made in the interface controllers of last versions

The basic differences of process of data transmission under reports SAE and ISO 9141, characteristic for the interface controllers of last versions, and also a data transmission order under report ISO 14230 are more low resulted:

Standard ISO 9141: the address byte Is added; Standard ISO 9141: return not one, and both key bytes (the additional byte comes back also in modes SAE, however here it is not used) Is carried out; Support of report ISO 14230 is added.

Connection installation

The order of installation of connection has not changed:

Report choice

The report gets out in as follows:

The remark and comments

If use of the controller for data transmission only on any one is planned or to two of reports, superfluous components can be excluded. For example, at the scheme organisation under report VPW (GM) in a wire of connection of the controller to the car three veins of electroconducting (the plug 16, 5 and 2) be required only.

If report PWM is not used, elements R4, R6, R7, R8, R9, R10, Т1, Т2 and D1 can be excluded.

At refusal of an exchange under report ISO elements are subject to an exception: R15, R16, R17, R18, R19, R21, Т4 and Т5.

Refusal of use of report VPW allows to exclude following elements: R13, R14, R23, R24, D2, D3 and Т3.

Ugolno-film resistors with the 5 percent admission of resistance are applied.

Pay attention to absence of the button of emergency reboot (RESET), - in case of need such reboot can be made by a detachment of the controller from an automobile socket (reboot of the interface processor will occur automatically). Software restart on PC leads to repeated initialization of the interface.