Mercedes S-Class W-140

1991-1999 of release

Repair and operation of the car

Mercedes S-Class
+ Mercedes-Benz cars of the class S (W-140)
+ Operation manual
+ Routine maintenance
+ Engine
+ Cooling systems, heating
+ Power supply system and release
- Engine electric equipment
   - Systems of ignition and engine management - the general information
      Checks of a control system of 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 air conditioner (AC)
      Application of an oscillograph for observation of signals of a control system
      Ignition coils - installation details
      Removal, installation and adjustment of the sensor of position of the camshaft (CMP)
      The distributor of ignition (M119.97 engines) - installation details
   + Systems of a charge and start
+ Gear shifting box
+ Automatic transmission
+ Coupling
+ Brake system
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment


Self-diagnostics of systems of electronic control of OBD

Several diagnostic devices making monitoring of separate parameters of systems of decrease in toxicity and fixing the revealed refusals in memory of the onboard processor in the form of individual codes of malfunctions are a part of the OBD system. The system makes also check of sensors and actuation mechanisms, controls vehicle service cycles, provides a possibility of storing even of the failures which are quickly arising in the course of work and cleaning of the block of memory.

All models described in the present manual 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 the data arriving from information sensors, and according to the basic parameters put in the processor memory, 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 the processor memory of OBD is made by means of the special scanner connected to the diagnostic socket of reading of the database (DLC) or by means of an auxiliary light-emitting diode and also by the codes highlighted on the display automatic by Quarter.

Data on diagnostic units

Check of serviceability of functioning of components of systems of injection and decrease in toxicity of the fulfilled gases is made by means of the universal digital measuring instrument (multimeter)

Connection of a multimeter to sockets of the control unit of the engine by means of an auxiliary splitter

Use of the digital measuring instrument is preferable 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 electronic components in the structure, such accuracy is of particular importance. The second, not less important, the fact that the internal contour of a digital multimeter, has rather high impedance is the reason (internal resistance of the device makes 10 megohms). As the voltmeter is connected to the checked chain in parallel, the accuracy of measurement of subjects is higher, than smaller current will pass through actually device. This factor is not essential at measurement of rather high values of tension (9 ÷ 12 V), however becomes defining at diagnostics of the elements giving low-voltage signals, such as, for example, l-probe where it is about measurement of shares of volt.

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

Special diagnostic scanners or testers with a certain cartridge (if it is provided), a universal cable and the socket can be used to diagnostics of electronic systems of the engine, automatic transmission, ABS, SRS and other. Besides, it is possible to use the expensive specialized automobile diagnostic computer which is specially developed for full diagnostics of the majority of systems of modern cars to this purpose (for example, ADC2000 of Launch HiTech). Also, it is possible to use 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 installed program OBD II browser.

You can also download the free version of a browser of OBD II for diagnostics of your car from the website of authors of the present manual

Some scanners, besides usual operations of diagnostics, allow to print out, at connection with the personal computer, the schematic diagrams of electric equipment which are stored in memory of the control unit (if are put), to program anticreeping system, to observe signals in car chains in real time.

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

Diagnostics of electronic control systems of 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 Location of the socket
4 — the 9-contact socket if it is established

The 9-contact socket for diagnostics of a control system 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 the blinking codes

Connect wires according to the scheme. The wire shown by a dash line is connected to a certain conclusion for diagnostics of a certain system (address 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, grounding of electronics)
Tension, contour 87
Tension, contour 30
System of electronic injection (diesel engines)
Injection of fuel with electronic distribution (diesel engines)
Consecutive electronic injection of fuel (diesel models)
System of the consecutive distributed injection/ignition HFM (engines 104)
System of the consecutive distributed LH injection (engines 104, 119, 120 [the rights.])
System of the consecutive distributed ME injection (engines 119, 120 [the rights.])
System of the consecutive distributed LH injection (engines 120 [a lion.])
System of the consecutive distributed ME injection (engines 120 [a lion.])
System of anti-blocking of brakes
Electronic traction control system
Adjustment of pro-slipping at acceleration
Program of electronic stabilization
Electronic acceleration
Control system of speed/stabilization of turns of idling
Basic module
Brake assistant
Automatic blocking of differential
Electronic control by transmission (AT 722.6)
Adaptive system of depreciation
System of hydrostrengthening of a wheel, sensitive to car speed
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 120 LH-SFI (lion.)
Combination of devices
Air conditioning system
System of ignition with the distributor, engines 104, 119 and 120 (the rights.)
TD signal (vremennua division) (diesel models)
TN signal, LH-SFI engines
System of ignition 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 of 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
Electronics of the engine (ME)
Food, C. 87
Traction control system (ETS)
Control unit of transmission (ETC)
The activity module (AAM - All Activity Module)
Security systems
Tire of data of CAN Low level
IC control panel
Plus batteries through a safety lock. Energized at any position of the lock of ignition, C. 30

Measurement of porosity of an impulse


1. At first take measurement of porosity of the impulses characterizing the work of a control system of quality of 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 will be 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 up to the working temperature.
4. Stop the engine and again include ignition. Read % instrument reading, and compare to the interpretation provided below. After start of the engine of instrument reading have to change, otherwise there is a malfunction.

Reading and removal of the 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 sec. (or 5-6 sec. on models with Bosch ECM-8/93) and release it. In 2 sec. the light-emitting diode will give a code which value is equal to the number of flashes. Duration of flash is 0.5 sec., an interval of 1 sec. Identify a code on the interpretation provided below. For reading of the following code press the button again. For deleting of this code press the button and hold it during 6-8 sec. (or 8-9 sec. 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 rechargeable battery.
4. Switch off ignition and disconnect the scheme for check.

The controller of interface of the personal computer to onboard system of self-diagnostics of OBD II under protocols of the SAE standards (PWM and VPW) and ISO 9141-2

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

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

General data

Scheme of the organization of the controller of interface to onboard system of self-diagnostics of OBD II

The considered device represents the microcontroller executed on KMOP (CMOS) technology. The device plays a role of the elementary scanner and is intended for reading of diagnostic codes and data of the OBD II system (engine turns, temperature of cooling liquid and the soaked-up air, load characteristics, a consumption of the air coming to 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 of rather 3-wire wire, connection to the diagnostic socket is carried out by a 6-wire wire. Supply voltage moves on the adapter via the 16-contact diagnostic OBD socket.

Recommendations about application

For connection of the device to the car the unscreened cable, no more than 1.2 m long can be used that has special value when using the PWM protocol. When using a cable of bigger length it is necessary to reduce resistance of resistors on an entrance of the device (R8 and R9 or R15). When using a screened cable, the screen should be switched-off for the purpose of decrease in capacity.

The cable for connection to a serial port of the computer can also be unscreened. The device steadily works with a cable up to 9 m long. With 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 use the additional shunting condensers.

The free software (browser) for reading of codes and data can be downloaded from the websites of producers, or the website of our publishing house and is intended for use under DOS. The insignificant size of a software application in option "under DOS" allows to accomodate it on the loading diskette DOS and to use even on the computers equipped with the software, incompatible with DOS. An optional condition is even existence in the computer of the hard drive.

General principles of data exchange

If 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 initsializatsionny exchange of office messages (handshaking). The device wiretaps the channel on existence of messages, executes the accepted commands and transfers results to the personal computer (PC) then immediately comes back to the listening mode. The data entering the controller and proceeding from it are organized in the form of a chain of the bytes which are consistently going one after another, first of which is control.

Usually control byte represents the number from 0 to 15 dec (in decimal calculation) (or 0-F hex) describing the number of the 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 the entering teams on poll of onboard system of self-diagnostics, and for the outgoing messages containing the requested information.

It is necessary to notice that in control byte only four younger bits are used, - the senior bits are reserved under some special teams and PC at initialization of connection with the controller and coordination of the protocol of data transmission can be used, and also the controller for control of errors of transfer. In particular, in case of a mistake by transfer, the controller makes installation of the senior meaning bit (MSB) of control byte in unit. By successful transfer all four senior bits are established in zero.

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

Initialization of the controller and onboard system of self-diagnostics

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

Connection installation

After connection of the controller to PC and the diagnostic OBD socket its initialization for the purpose of prevention of the "lags" connected with noise in consecutive lines has to be made in case their connection was made before inclusion of power supply of the controller. 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 controller as the command for connection installation is sent. In reply the controller instead of control sends the only byte of FF hex (255 dec) and passes into 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 controller does not use control byte.


At this stage initialization of the protocol under 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 (Asian/European producers).

There is a set of exceptions: so, for example, at poll of some models of the Mazda cars the "Ford" 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 the byte defining protocol type following directly it: 0 = VPW, 1 = PWM, 2 = ISO 9141. So, for example, at the command of 41 02 hex initialization of the ISO 9141 protocol is made.

In reply the controller sends control byte and byte of a state. The MSB installation of control byte speaks about existence of problems, at the same time the byte of a state following it will contain the relevant information. At successful initialization the control byte of 01 hex indicating that the verification byte of a state follows further is sent. In case of the VPW and PWM protocols the verification byte represents a simple echo of the byte defining the protocol (0 or 1, respectively), at initialization of the ISO 9141 protocol it will be the digital key returned by the onboard OBD processor and defining what of two versions of the protocol which are 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 happens much quicker as demands only transfer of the relevant information to the controller.

On the models meeting ISO, initialization takes about 5 seconds spent for the information exchange of the adapter with the onboard processor made with a speed of 5 baud.

It is necessary to draw the attention of the reader that on some models of cars of the 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 has to make automatic delivery of inquiries each several seconds, even in the single mode.

After installation of connection and initialization of the protocol regular data exchange, consisting of the inquiries arriving from PC and the answers issued by the adapter begins.

Data exchange order

Functioning of the controller when using protocols of the ISO 9141-2 and SAE family (VPW and PWM) happens according to a little various scenarios.

Exchange under the SAE protocols (VPW and PWM)

At data exchange under these protocols there is a buffering of only one shot of data that means need of a specification subject to capture or return of a shot. The onboard processor can transfer the packages consisting more than of one shot in some (rare) cases. In such situation the inquiry has to repeat until all shots of a package are not accepted.

The inquiry is always formed as follows: [Control byte], [Inquiry according to the SAE standard], [Number of a shot]. As it was already mentioned above, the control byte usually represents the number equal to the 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), the 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, a consumer of control byte and number of a shot is the interface controller.

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

At failure the 2-byte response message is sent: [Control byte], [State byte]. At the same time in control byte the MSB installation is made. Four younger bits form number 001 demonstrating that control is followed by the only byte - state byte. This situation can arise rather often as Specifications allow a possibility of a lack of distribution the onboard processor of data, and also transfer of incorrect data in case the inquiry does not conform to the standard supported by producers of the car. Also the situation when required data are absent in random access memory of the processor of time at the moment is possible. When the controller does not receive the expected answer, or obtains the damaged data, the MSB installation of control byte is made, and after control the state byte is given.

At collisions in the tire the interface develops the only byte of 40 hex which is control byte with the nullified younger bit. The similar situation can arise rather often when loading a car tire messages of higher than at diagnostic data of a priority, - the computer has to repeat initial inquiry.

Exchange under the ISO 9141-2 protocols

ISO 9141-2 is used by most of Asian and European producers of automotive vehicles. The structure of the formed PC of inquiry a little in what differs from used in the SAE standards, with only that difference that the adapter does not need information on number of a shot and the relevant data should not be present at a package. Thus, the inquiry always consists of control byte and the chain of the information bytes including checksum following it. As the response message the controller just relays the signals created by the onboard processor. The control byte in the response message is absent therefore PC perceives the arriving information a continuous stream until the chain is not interrupted by the 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 controller does not make the analysis of shots, does not reject not diagnostic shots, etc. PC has to make by own forces processing of the arriving data with the purpose of exarticulation of separate shots by the analysis of heading bytes.

Responses to the majority of inquiries consist of the only shot.

Modifications of controllers of the latests version

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

The symbol XX means the uncertain, reserved or unknown byte.

The main differences of process of data transmission under the SAE and ISO 9141 protocols, characteristic of the interface controllers of the latests version, and also a data transmission order under the ISO 14230 protocol are given below:
   1) ISO 9141: The address byte is added;
   2) ISO 9141: Return not of one, but both key bytes is carried out; (the additional byte comes back also in the SAE modes, however here it is not used).
   3) Support of the ISO 14230 protocol is added.

Connection installation

The order of installation of connection did not change:

Sending: 20

Choice of the protocol

The protocol is chosen 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, K1, K2, where K1, K2 - key bytes of ISO
Or: 82, XX, XX (error of initialization of ISO 9141)
ISO 14230 (bystry initialization):
46, 03, R1, R2, R3, R4, R5, where: R1 ÷ R5 - the message on the beginning of request of ISO 14230 on connection installation, usually R1 ÷ R5 = C1, 33, F1, 81, 66
S1, S2, … … …, where S1, S2, … … … - the message on the beginning of the response of ISO 14230 to connection installation

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

Typical affirmative answer looks as follows:

S1, S2, … …. = 83, F1, 10, S1, E9, 8F, BD
ISO 14230 (slow initialization):
Similar to ISO 9141

Remark and comments

If use of the controller for data transmission only on any to one is planned or to two of protocols, excess components can be excluded.

For example, at the organization of the scheme under the VPW (GM) protocol in a wire of connection of the controller to the car only three veins of an electrical wiring (plug 16, 5 and 2) will be required.

If the PWM protocol is not used, the R4, R6, R7, R8, R9, R10, T1, T2 and D1 elements can be excluded.

At refusal of exchange under the ISO protocol elements are subject to an exception: R15, R16, R17, R18, R19, R21, T4 and T5.

The 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 used.

Pay attention to lack of the button of emergency reset (RESET), - in case of need such reset can be made by a controller detachment from the automobile socket (reset of the interface processor will happen automatically). Restart of the software on PC leads to repeated initialization of the interface.