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System of onboard self-diagnostics (OBD) - the general information
System of onboard self-diagnostics (OBD) - the general information
General description
Task of any onboard system of self-diagnostics (OBD) is identification of refusals and violations of functioning of under control systems with entering in memory of the processor of the corresponding diagnostic codes (DTC) and the notification of the driver about the violation fact (usually by means of built in in a combination of devices of a control lamp of refusals of MIL / «Check the engine»).
Besides the DTC code in memory of ECM it is fixed also current working parameters of the engine at the moment of violation identification.
At violation of serviceability of functioning of the information sensors which are taking part in management process by the engine, ECM can make switching of systems in emergency operation. The base working parameters providing adequate operation of the engine are thus activated (some absolute pseudo-signal of the faulty sensor is feigned directly by the management module), however with inevitable decrease in efficiency of its return and increase in fuel consumption, - the car should be driven away on car repair shop for the purpose of identification and elimination of causes of failure.
The structure of OBD system includes some diagnostic devices making monitoring of separate parameters 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 makes also check of sensors and actuation mechanisms, supervises operational cycles of a vehicle, provides possibility of freezing of parameters and cleaning of the block of memory.
Models considered in the real Management are completed with system of onboard diagnostics of the second generation of the SAE standard (OBD II). A basic element of any OBD system is the onboard processor more often called by the electronic module of management (ECM). ECM is a brain of a control system of the engine. Basic data, and also signals of registered OBD of refusals and violations arrive on the module from various information sensors 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 self-diagnostics function with the feedback, allowing to minimize effect of errors of the main equipment of entrance and target paths of ECM is provided.
Principle of the organization of function of self-diagnostics of ECM on diesel models
Data read-out of memory of the OBD processor is made by means of the special scanner (HI-Scan type) connected to the 20-contact diagnostic socket of reading of a database (DLC), fixed on the air purifier 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 dashboard.
Diagnostic DLC sockets allow to make reading of codes of malfunctions by means of the special scanner
On service of components of control systems of engine/decrease in toxicity of the fulfilled gases special guarantee certificates with the prolonged validity period extend. It is not necessary to undertake attempts of independent performance of problem diagnostics of ECM or replacement of components of system, to an exit of terms of these obligations, - address to specialists of firm car repair shops of the KIA company.
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 several reasons. First, on analog devices it is rather difficult (sometimes, 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 rather high impedance (internal resistance of the device makes 10 megohms). As the voltmeter is connected to a checked chain in parallel, accuracy of measurement by that is higher, than the smaller parasitic current will pass through actually device. This factor is not essential at measurement of rather high values of tension (9 ÷ 12 In), however there is defining at diagnostics of elements giving out low-voltage signals, such, as, for example, a lambda probe where it is a question of measurement of shares of volt.
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Use at diagnostics of considered systems of a digital multimeter with a high impedance essentially increases accuracy of the measurements made in a low-voltage range. |
Parallel monitoring of parameters of signals, resistance and tension in all chains of management can be made by means of a splitter connected consistently to the socket of the module of management (ECM). Measurement of parameters of signals on splitter plugs in various modes of functioning of the engine allows to define current state of the last and to reveal taking place violations.
At diagnostics of electronic control systems by the engine, transmission, ABS and SRS special scanners of the SAE (GST) standard to which number the HI-Scan scanner belongs also are applied. Many SAE scanners 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 regions of the world (Europe, Asia, the USA etc.). Connection of the scanner is made to onboard DLC.
Alternative way of data read-out of OBD is connection to system of the personal computer equipped with a special cable and equipped with the software of OBD.
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More detailed information to data read-out by means of scanners can be learned on sites www.obdii.com, www.obd-2.com and www.obd-2.de.
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The universal adapter To - L-Line (www.autoelectric.ru) serves for coordination of signals of RS-232 port and ISO-9141 (K-Line) and ALDL interfaces. The various cables can be connected to sockets of the adapter, allowing to make OBD data read-out from cars of various brands. The switches provided on the adapter and elements of indication 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 marking of L-Line testifies to connection of the line L with mass of the car. Activation of a red light-emitting diode with marking K-Line confirms about presence on lines K at the moment time of high potential. At the established communication with car OBD system 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 a transitional cable RS232 25-9.
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Universal K-L-Line adapter. |
Some input readers besides usual diagnostic operations allow at connection to the personal computer to make a raspechatyvaniye being stored in memory of the module of management of schematic diagrams of the various equipment (if those are put in ECM), to program anticreeping system and control units of various devices of the car, and also in real time to observe signals in electric chains of the car.
Reading of the DTC codes
Cleaning of memory of system of self-diagnostics
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Alternatively cleaning of memory of the OBD II processor can be made by means of the scanner connected to DLC. |
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For a while more than 20 seconds disconnect a negative wire from the battery.
After connection of the battery connect the input reader to DLC and include ignition.
Start the engine and let's to it work about three minutes with turns 2000 in a minute.
Make sure of absence in memory of the processor of codes of malfunctions (DTC).
In case of need make the corresponding regenerative repair and repeat procedure of cleaning of memory.
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Connection of the personal computer to onboard system of self-diagnostics of OBD II by means of the interface BR16F84-1.0 controler according to protocols of the SAE standards (PWM and VPW) and ISO 9141-2
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The controler is not intended connections to onboard systems of self-diagnostics of the first generation (OBD I)! |
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To the VPW standard models of production of the company GM, PWM - Ford answer, to ISO 9141-2 - Asian and European models. |
General information
The scheme of the organization of connection of PC to the diagnostic DLC socket of onboard system of self-diagnostics of OBD II by means of the BR16F84-1.0 controler
The considered device represents the microcontroller executed on KMOP technologies (CMOS). The device plays a role of the elementary scanner and is intended for reading of diagnostic codes and OBD II system data (engine turns, temperature of cooling liquid and soaked-up air, loading characteristics, a consumption of air arriving in the engine, etc.) within the SAE standard J1979 specification via the tire of any execution (PWM, VPW and ISO 9141-2).
Main destination
For connection to the computer it is enough 3-жильного a wire, connection to the diagnostic socket is carried out 6-жильным by a wire. The supply voltage moves on the controler via the 16-contact diagnostic OBD socket.
Recommendations about application
For device connection to the car the neekranirovanny cable, length no more than 1.2 m that has special value when using PWM protocol can be used. When using a cable of bigger length it is necessary to reduce resistance of resistors on a device entrance (R8 and R9 or R15). When using an ekranirovanny cable, the screen should be disconnected for the purpose of decrease in capacity.
The cable for connection to a serial port of the computer also can be neekranirovanny. The device stably works with a cable in length to 9 m. At much bigger length of a cable it is necessary to use more powerful communicator of RS 232.
The topology of electric connections is any. At the increased humidity apply additional shunting condensers.
General principles of data exchange
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If the opposite is not stipulated especially, all numbers are given in a 16-richny format (hex), - the decimal format is designated by well-aimed dec. |
Data exchange goes on three-wire consecutive connection without application of an initsializatsionny exchange by office messages (handshaking). The device listens to the channel on existence of messages, executes accepted teams and transfers results to the personal computer (PC) then immediately comes back to a listening mode. Entering into the controler and data starting with it are organized 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 number of information bytes following further. So, for example, the 3-byte team will look as follows: 03 (control byte), 1st byte, 2nd byte, 3rd byte. The similar format is used as for entering commands for poll of onboard system of self-diagnostics, and for the outgoing messages containing 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 teams and PC can be used at initialization of connection with the controler and coordination of the protocol of data transmission, and also the controler for control of errors of transfer. In particular, in case of a mistake by transfer, the controler makes installation of the senior meaning bit (MSB) of control byte in unit. By successful transfer all four senior bits are established in a zero.
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There are separate exceptions to the rules of use of control byte. |
Initialization of the controler and onboard system of self-diagnostics
To start data exchange of PC should make installation of connection with the controler, then initialize the controler and the channel of data of OBD II.
Connection installation
After controler connection to PC and the diagnostic OBD socket its initialization for the purpose of prevention of the "lags" connected with noise in consecutive lines in case their connection should be made was made before inclusion of a food of the controler. The simplest check of activity of the interface is at the same time made. First of all the one-byte signal of 20 hex perceived by the controler as command for installation of connection is sent. In reply the controler instead of the control sends the unique byte of FF hex (255 dec) and passes to a waiting mode of reception of data. Now PC can pass to initialization of the channel of data.
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This case is one of the few when the controler does not use control byte. |
Initialization
At this stage protocol initialization on which data exchange will be made, and in case of the ISO protocol – initialization of onboard system is made. Data exchange is made on one of three protocols: VPW (General Motors), PWM (Ford) and ISO 9141-02 (the Asian/European producers).
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There is a set of exceptions: so, for example, at poll of some models of Mazda cars the "fordovsky" PWM protocol can be used. Thus, at emergence of problems of transfer it is necessary first of all to try to use any other protocol. The choice of the protocol is made by transfer of the combination consisting of control byte of 41 hex and byte following directly it, the protocol defining type: 0= VPW, 1 = PWM, 2 = ISO 9141. So, for example, at the command of 41 02 hex ISO 9141 protocol initialization is made. |
In reply the controler sends control byte and condition byte. The MSB installation of control byte speaks about existence of the problems, the byte of a condition thus following it will contain the relevant information. At successful initialization the control byte of 01 hex specifying is sent that the verifikatsionny byte of a condition further follows. In case of the VPW and PWM protocols the verifikatsionny byte represents a simple echo of byte defining the protocol (0 or 1, respectively), at ISO 9141 protocol initialization it will be the digital key returned by the onboard OBD processor and defining which of two versions of the protocol slightly differing from each other will be used.
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The digital key has purely information appointment. It is necessary to notice that initialization of the VPW and PWM protocols occurs much quicker as demands only transfer of the relevant information to the controler. On the models answering to the ISO standard, initialization takes about 5 seconds, spent for information exchange of the controler with the onboard processor, the 5th baud made with a speed. It is necessary to pay attention of the reader that on some models of cars of ISO family 9141 initialization of the protocol stop, if the request for issue of data is not transferred during a 5-second interval, - told means that PC should make automatic delivery of inquiries everyone some seconds, even in a single mode. |
After installation of connection and initialization of the protocol the regular data exchange, consisting of inquiries arriving from PC and answers issued by the controler begins.
Data exchange order
Controler functioning when using protocols of ISO 9141-2 and SAE family (VPW and PWM) occurs according to a little various scenarios.
Exchange according to the SAE protocols (to VPW and PWM)
At data exchange according to these protocols there is a buffering only one shot of data that means need of a specification subject to capture or shot return. In some (rare) cases the onboard processor can transfer the packages consisting more than of one shot. In such situation the inquiry should repeat until all shots of a package will not be accepted.
The inquiry is always formed as follows: [Control byte], [Inquiry on the SAE standard], [Shot number]. As it was already mentioned above, the control byte usually represents the number equal to full number of the following bytes behind it. The inquiry is made out according to the SAE J1950 and J1979 Specifications and consists of heading (3 bytes), sequence of information bytes and byte of control of a mistake (CRC). Let's notice that while information on inquiry is formed in strict compliance with the SAE Specifications, the consumer of control byte and number of a shot is the interface controler.
At a successful conclusion of procedure the response message always has the following format: [Control byte], [The answer on the SAE standard]. The control byte, as well as earlier, defines number of information bytes following it. The answer according to requirements of the SAE standard consists of heading (3 bytes), a chain of information bytes and CRC byte.
At failure the 2-byte response message is sent: [Control byte], [Condition byte]. Thus in control byte the MSB installation is made. Four younger bits form number 001, testifying that the control is followed by the unique byte, - condition byte. This situation can arise rather often as Specifications allow possibility of a lack of distribution the onboard processor of data, and also transfer of incorrect data in a case when the inquiry does not correspond supported by producers of the car to a standard. The situation when required data are absent in random access memory of the processor at the moment time is possible also. When the controler does not receive the expected answer, or obtains the damaged data, the MSB installation of control byte is made, and after the control the condition byte stands out.
At collisions in the tire the interface develops the unique byte of 40 hex being control byte with the nulled younger bit. The similar situation can arise rather often when loading a car tire by messages of higher than at diagnostic data of a priority, - the computer should repeat initial inquiry.
Exchange according to the ISO 9141-2 protocols
The ISO 9141-2 standard is used by the majority of Asian and European producers of automobile equipment. The structure of formed PC of inquiry a little than differs from used in the SAE standards, with that only a difference that the controler does not need in information on number of a shot and the relevant data to be present at a package should not. Thus, the inquiry always consists of control byte and a chain of the information bytes including checksum following it. As the response message the controler simply relays the signals created by the onboard processor. The control byte in the response message is absent, therefore PC perceives arriving information a continuous stream until the chain does not interrupt a pause in 55 milliseconds, reporting about end of information package. Thus, the response message can consist of one or more shots according to requirements of the SAE J1979 specifications. The controler does not make the analysis of shots, does not reject not diagnostic shots etc. PC should make own forces processing of arriving data with the purpose of exarticulation of separate shots by the analysis of heading bytes.
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Answers to the majority of inquiries consist of the unique shot. |
The updatings made in the interface controlers of the last versions
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All information bytes are transferred in a 16-richny format (hex). |
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The symbol of XX means the uncertain, reserved or unknown byte. |
Below the main differences of process of data transmission according to the SAE and ISO 9141 protocols, characteristic for the interface controlers of the last versions, and also a data transmission order according to the ISO 14230 protocol are given:
ISO 9141 standard: The address byte is added;
ISO 9141 standard: Return not one, and both key bytes (the additional byte comes back also in the SAE modes, however here it is not used) is carried out;
ISO 14230 protocol support is added.
Connection installation
The order of installation of connection did not change:
| Sending: |
20 |
| Reception: |
FF |
Protocol choice
The protocol gets out in as follows:
| VPW: |
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41, 00 |
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02, 01, XX |
| PWM: |
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41, 01 |
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02, 01, XX |
| SO 9141: |
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42, 02, adr, where: adr - address byte (usually 33 hex) |
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02, К1, К2, where К1, К2 - key bytes of ISO |
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82, XX, XX (error of initialization of ISO 9141) |
| ISO 14230 (fast initialization): |
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46, 03, R1, R2, R3, R4, R5, where: R1 ÷ R5 - the message on the beginning of inquiry of ISO 14230 on connection installation, usually R1 ÷ R5 = С1, 33, F1, 81, 66 |
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S1, S2, … … …, where S1, S2, … … … - the message on the beginning of the answer of ISO 14230 on connection installation |
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Can consistently be transferred more than one ECU. As the answer the negative code of the answer can be used.
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| The typical affirmative answer looks as follows: |
S1, S2, … …. = 83, F1, 10, С1, Е9, 8F, BD |
| ISO 14230 (slow initialization): |
ISO 9141 is similar |
Remark and comments
If controler use for data transmission only on any to one is planned or to two of protocols, superfluous components can be excluded. For example, at the scheme organization under the VPW (GM) protocol in a wire of connection of the controler to the car three veins of electroconducting (plug 16, 5 and 2) be required only.
If the PWM protocol is not used, the elements R4, R6, R7, R8, R9, R10, Т1, Т2 and D1 can be excluded.
At refusal of an exchange according to the ISO protocol elements are subject to an exception: R15, R16, R17, R18, R19, R21, Т4 and Т5.
Refusal of use of the VPW protocol allows to exclude the following elements: R13, R14, R23, R24, D2, D3 and T3.
Coal and film resistors with the 5 percent admission of resistance are applied.
Pay attention to lack of the button of emergency reset (RESET), - in case of need such reset can be made by a way of a detachment of the controler from the automobile socket (reset of the interface processor will occur automatically). Software restart on PC leads to repeated initialization of the interface.