Mercedes S-Class W-140

1991-1999 of release

Repair and car operation

Mercedes S-Class
+ Mercedes-Benz Cars of a class S (W-140)
+ Operation manual
+ Routine maintenance
+ Engine
+ 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
      Spark plugs
      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
+ Coupling
+ Brake system
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment


Self-diagnostics of systems of electronic control of OBD

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 vehicle service cycles, provides storing possibility even failures quickly arising in the course of work and cleaning of the block of memory.

All models described in the real Management are equipped with system of onboard diagnostics (OBD).

Basic element of system is the onboard processor more often called by the electronic module of management (ESM), or the module of management of functioning of the power unit (RSM)

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 read-out of memory of the OBD processor is made by means of the special scanner connected to the diagnostic socket of reading of a database (DLC) or by means of an auxiliary light-emitting diode, and also on the codes highlighted on the display automatic Quarter.

Data on diagnostic devices

Check 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.

Parallel supervision of parameters of signals, resistance and tension in all chains of management is possible by means of a splitter included consistently in the socket of the control unit by the engine. Thus on the switched-off, working engine or during car movement, measurement of parameters of signals on splitter plugs from what the conclusion about possible defects is drawn is made.

Special diagnostic scanners or testers can be applied to diagnostics of electronic systems of the engine, automatic transmission, ABS, SRS and other with a certain cartridge (if it is provided), a universal cable and the socket. Besides, it is possible to apply the expensive specialized automobile diagnostic computer which has been specially developed for complete diagnostics of the majority of systems of modern cars to this purpose (for example, Launch HiTech firm ADC2000). Also, it is possible to apply scanners and specialized diagnostic analyzers to this purpose, for example FDS 2000, Bosch FSA 560 (, KTS500 (0 684 400 500) or the ordinary personal computer with the special adapter, a cable (for example, a set 1 687 001 439) and the established program OBD II browser.

For diagnostics of your car you can download the free version of a browser of OBD II also from a site of originators of the real Management

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.

It is necessary to carry out some checks on different diagnostic sockets. First of all make check of porosity of an impulse.

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 sockets

Arrangement of diagnostic sockets

2 — the 38-contact socket if it is established
3 — the socket Location
4 — the 9-contact socket if it is established

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)

1 — a TD switchboard Conclusion
2 — the Case
3 — diagnostics Conclusion
4 — the Conclusion of 1 coil of ignition

5 — the Conclusion of the 15th coil of ignition
6 — the Conclusion +30
7 and 9 — Conclusions to the VMT sensor
8 — the Screen

Purpose of contacts of the 38-contact diagnostic socket

The 38-contact diagnostic socket for extraction of blinking codes

Connect wires according to the scheme. The wire shown by the faltering line, is connected to a certain conclusion for diagnostics of a certain system (address to the list of purpose of contacts):

To a conclusion 4 — for diagnostics of system of injection;
To a conclusion 8 — for diagnostics of the main unit;
To a conclusion 17 — for diagnostics of system of ignition;
To a conclusion 19 — for check of the block of diagnostics.

Plugs of the socket have the following appointment:

conclusion No.


Weight, contour 31 (W12, W15, electronics grounding)
Tension, contour 87
Tension, contour 30
System of electronic injection (diesel engines)
Fuel injection with electronic distribution (diesel engines)
Consecutive electronic injection of fuel (diesel models)
System consecutive distributed injections/ignitions HFM (engines 104)
System of the consecutive distributed injection of LH (engines 104, 119, 120 [the rights.])
System of the consecutive distributed injection of ME (engines 119, 120 [the rights.])
System of the consecutive distributed injection of LH (engines 120 [a lion.])
System of the consecutive distributed injection of ME (engines 120 [a lion.])
System of anti-blocking of brakes
Electronic antiprobuksovochny system
Pro-slipping adjustment at acceleration
Program of electronic stabilization
Electronic acceleration
Control system of speed/stabilization of turns of idling
Base module
Brake assistant
Automatic blocking of differential
Electronic control (AT 722.6) transmission
Adaptive system of amortization
Sensitive to speed of the car system of hydrostrengthening of a wheel
TNA signal (petrol models), LH-SFI engines
TN signal (petrol models), HFM (ME) engines - SFI
Signal, information on porosity, engines 119, 120 LH-SFI (rights.)
Signal, information on porosity, engines of 120 LH-SFI (lion.)
Combination of devices
Air central air
Ignition system with the distributor, engines 104, 119 and 120 (the rights.)
TD signal (временнуе division) (diesel models)
TN signal, LH-SFI engines
Ignition system with the distributor, LH-SFI engines
Diagnostic module
Pneumatic equipment
Anticreeping alarm system
Are not used
Parktronic system
It is not used
Safety pillows / натяжители ETR (SRS) belts
Remote control by the uniform lock
Are not used
Communication system and navigation
It is not used

Arrangement of the 16-contact diagnostic socket (on the USA models)

Identification of plugs of the 16-contact diagnostic socket of system of onboard diagnostics (on the USA models)

Plugs of the socket have the following appointment:

conclusion No.


TNA signal
Connection with the case, plug 31
The case - an alarm conclusion, the plug 31
Tire of data of CAN high level
Engine (ME) electronics
Food, C. 87
Antiprobuksovochny system (ETS)
Control unit transmission (ETC)
The activity module (AAM - All Activity Module)
Safety systems
Tire of data of CAN Low level
IC control panel
Battery plus through a safety lock. Energized at any position of the lock of ignition, C. 30

Measurement of porosity of an impulse


1. At first carry out measurement of porosity of the impulses characterizing work of a control system of quality of a mix and its malfunction, repeating at the last four starts of the engine. For this purpose the device for measurement of so-called duration of the closed condition of contacts of the breaker (dwell-meter), a tester a lambda probe or a digital multimeter is required.
2. Connect + a device conclusion to the 3rd contact of the 9-contact socket and negative to the car case.
3. Start and warm up the engine to working temperature.
4. Stop the engine and again include ignition. Remove % instrument reading, and compare to the interpretation specified below. After start of the engine of instrument reading should change, otherwise there is a malfunction.

Reading and removal of blinking codes


1. Reading of codes is made by means of the simple scheme from the push-button switch and a light-emitting diode. Depending on type of the diagnostic socket and the system subjected to diagnostics, connect the scheme according to an illustration.
2. Include ignition.
3. Press and hold the switch button during 2-4 seconds (or 5-6 seconds on models with Bosch ECM-8/93) and release it. In 2 seconds the light-emitting diode will give out a code which value is equal to number of flashes. Duration of flash of 0.5 seconds, interval of 1 second. Identify a code by the interpretation specified below. For reading of the following code again press the button. For deleting of this code press the button and hold it during 6-8 seconds (or 8-9 seconds on models with Bosch ECM-8/93). Besides, on some models, deleting of codes in memory is possible at shutdown of the negative plug of the storage battery.
4. Switch off ignition and disconnect the scheme for check.

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

The controler is not intended connections to onboard systems of self-diagnostics of the first generation (OBD I)!

To the VPW standard models of production of the company GM, PWM - Ford answer, to ISO 9141-2 - Asian and European models.

General data

Scheme 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 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 adapter 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.

The free software (browser) for reading of codes and data can be downloaded from sites of producers, or a site of our publishing house 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

If the opposite is not stipulated especially, all numbers are given in a 16-richny format (hex).

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.

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.

This case is one of the few when the controler does not use control byte.


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).

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.

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 adapter 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 adapter 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 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.

Answers to the majority of inquiries consist of the unique shot.

Updatings of controlers of the last versions

All information bytes are transferred in a 16-richny format (hex).

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:
   1) ISO 9141 standard: The address byte is added;
   2) ISO 9141 standard: Return not one, and both key bytes is carried out; (the additional byte comes back also in the SAE modes, however here it is not used).
   3) ISO 14230 protocol support is added.

Connection installation

The order of installation of connection did not change:

Sending: 20

Protocol choice

The protocol gets out in as follows:

41, 00
02, 01, XX
41, 01
02, 01, XX
ISO 9141:
42, 02, adr, where: adr - address byte (usually 33 hex)
02, К1, К2, where К1, К2 - key bytes of ISO
Or: 82, XX, XX (error of initialization of ISO 9141)
ISO 14230 (fast initialization):
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
S1, S2, … … …, where S1, S2, … … … - the message on the beginning of the answer of ISO 14230 on connection installation

Can consistently be transferred more than one ECU. As the answer the negative code of the answer can be used.

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.