Mercedes S-Class W-140
1991-1999 of release
Repair and car operation
+ Mercedes-Benz Cars of a class S (W-140)
+ Operation manual
+ Routine maintenance
+ Systems of cooling, heating
+ Power supply system and release
- Engine electric equipment
- Ignition and engine management systems - the general information
Checks of a control system by ignition and injection
Search of malfunctions - the general information and preliminary checks
Check and adjustment of a corner of an advancing of ignition
Self-diagnostics of systems of electronic control of OBD
Diagnostics of electronic system of the automatic conditioner of air (KV)
Oscillograph application for supervision of signals of a control system
Ignition coils - installation details
Removal, installation and adjustment of the sensor of provision of a camshaft (CMP)
The ignition distributor (M119.97 engines) - installation details
+ charge and start Systems
+ gear shifting Box
+ Avtomaticheckaya transmission
+ Brake system
+ Suspension bracket and steering
+ Onboard electric equipment
Self-diagnostics of systems of electronic control of OBD
ECM/PCM is a brain of a control system of the engine. Basic data arrive on the module from various information sensors and other electronic components (switches, the relay etc.). On the basis of the analysis of data arriving from information sensors, and according to put in memory of the processor in base parameters, ECM/PCM develops commands for operation of various operating relays and actuation mechanisms, carrying out thereby adjustment of working parameters of the engine, and providing maximum efficiency of its return at the minimum fuel consumption.
Data on diagnostic devicesCheck of serviceability of functioning of components of systems of injection and decrease in toxicity of the fulfilled gases is made by means of a universal digital measuring instrument (multimeter)
Multimeter connection to control unit sockets the engine by means of an auxiliary splitter
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 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 l-probe where it is a question of measurement of shares of volt.
Some scanners, besides usual operations of diagnostics, allow, at connection with the personal computer, to unpack being stored in memory of the control unit schematic diagrams of electric equipment (if are put), to program anticreeping system, to observe signals in car chains in real time.
Diagnostics of electronic control systems by the engine, injection and ignition, automatic conditioner of air and ABS/ASR/ETS/ESP
Scheme of an arrangement and design of diagnostic socketsArrangement of diagnostic sockets
The 9-contact socket for control system diagnostics on value of porosity of an impulse, by means of the device for measurement of so-called duration of the closed condition of contacts of the breaker (dwell-meter)
Purpose of contacts of the 38-contact diagnostic socketThe 38-contact diagnostic socket for extraction of blinking codes
Plugs of the socket have the following appointment:
Arrangement of the 16-contact diagnostic socket (on the USA models)
Plugs of the socket have the following appointment:
Measurement of porosity of an impulse
Reading and removal of blinking codes
The controler of interface of the personal computer with onboard system of self-diagnostics of OBD II according to protocols of the SAE standards (PWM and VPW) and ISO 9141-2
General dataScheme of the organization of the controler of interface to onboard system of self-diagnostics of OBD II
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 J1979 standard via the tire of any execution (PWM, VPW and ISO 9141-2).
Main destinationFor 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 adapter via the 16-contact diagnostic OBD socket.
Recommendations about applicationFor 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.
The free software (browser) for reading of codes and data can be downloaded from sites of producers, or a site of our publishing house arus.spb.ru and is intended for use under DOS. The insignificant size of a program application in option «under DOS» allows to contain it on the loading diskette DOS and to use even on the computers equipped with the software incompatible with DOS. An unessential condition is even existence in the computer of a hard disk.
General principles of data exchange
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.
Initialization of the controler and onboard system of self-diagnosticsTo 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 installationAfter 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.
InitializationAt 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).
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.
After installation of connection and initialization of the protocol the regular data exchange, consisting of inquiries arriving from PC and answers issued by the adapter begins.
Data exchange orderControler 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 protocolsThe 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 adapter 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.
Updatings of controlers of the last versions
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:
Connection installationThe order of installation of connection did not change:
Protocol choiceThe protocol gets out in as follows:
The typical affirmative answer looks as follows:
Remark and commentsIf 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.