Mercedes S-Class W-140

1991-1999 of release

Repair and operation of the car

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).

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

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 (www.bosch.de), 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.

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

Purpose of contacts of the 38-contact diagnostic socket

Plugs of the socket have the following appointment: