Mercedes M-Class W163

since 1997 of release

Repair and car operation

Search of causes of failures of electric equipment

Described below procedure allow to make the general diagnostics of a condition of the main electric contours, electronic modules of management however should not be applied to check of electric systems open to injury, in particular, including in the structure!

General information

The typical electric contour consists of the consumer of the electric power (a working element), a set of switches, the relay, executive electromotors, safety locks, the fusible inserts/breakers of a chain concerning work of this element, and also connecting electroconducting, its contact plugs and sockets. For the purpose of simplification of performance of diagnostic procedures schemes of electric connections of systems of onboard electric equipment are provided in the last Section of the present Chapter.

Before starting search of causes of failure of the failed consumer of the electric power, attentively study the corresponding electric circuit, try as it is possible to imagine more clearly a principle of functioning of the elements which are a part of the suspected contour. The list of possible causes of failure can be minimized by a way of an exception of it regularly functioning components concerning work of the checked contour. At simultaneous violation of functioning at once several components, the most probable cause of refusal is failure of the general for the corresponding chains insert safety lock/melting, or grounding violation.

More often refusals of electric equipment speak the elementary reasons, such as oxidation, or weakening of fastening of terminal connections, failure of a safety lock or a fusible insert, failure of the relay, etc. Before starting search of internal defects of actually refused component, attentively check a condition of all safety locks concerning its functioning, sockets and connecting wires (see. Section Digital tire of data of CAN).

For definition of the list of knots subject to check and contact sockets, study the corresponding schemes of electric connections (see. Schemes of electric connections).

To number of the diagnostic equipment more often used by search of refusals of electric equipment, it is necessary to carry a universal measuring instrument the chain/voltmeter (the 12-voltny lamp also will be suitable for some checks with a set of connecting wires), a lamp sampler with the individual power supply (sometimes called also a conductivity measuring instrument), an ohmmeter, the power supply with a set of connecting wires, and also a set of the wires crossing points, equipped various type connecting plugs and, - it is desirable, - the built-in breaker of a chain or a safety lock (for shunting of suspicious sites of a chain or electric components). Before resorting to use of the diagnostic equipment attentively study the scheme of electric connections of components of the corresponding contour.

At identification of the reason of refusal having unstable character (violations such usually appear connected with oxidation of contact plugs, or weakening of fastening of terminal connections of electroconducting) the simplest check of a chain which is carried out by twitching of various sites of electroconducting of the corresponding contour as a result of which the defective piece of a chain is localized can be made. This check can be made together with any of listed below in the corresponding subsections.

Except the problems connected with violation of quality of electric connections, it is necessary to refer breaks and short circuits to number of the most probable and often occurring refusals of electric contours in a chain.

Chain break usually is caused by mechanical injury of tokoprovodny veins or a detachment of contact plugs that leads to disconnection of an electric contour and the circulation termination in it an electric current. As a result of chain break its working component ceases to function, however the corresponding safety locks / fusible inserts do not fail.

Short circuit of its electroconducting is called as short circuit unforeseen a chain design. Thus the current starts to circulate on the shortest way, in most cases leaving on weight. Short circuits appear connected with violation of integrity of isolation of electroconducting more often and without fail lead to failure of the corresponding safety locks / fusible inserts.

Tension stock-taking in a chain

PERFORMANCE ORDER

Stock-taking of tension is included into number of standard checks in default any consumer of the electric power. Connect one of wires («-») a chain/voltmeter measuring instrument to the negative plug of the battery, or any of reliably earthed points on the car chassis/engine. The second wire of the device connect to the terminal connection of a checked contour preferably closest to the battery or a safety lock. Submit a food to a contour. Do not forget that some chains запитываются only in certain positions of the switch of ignition. If tension takes place (the measuring instrument lamp joins, or on the indicator of the voltmeter the corresponding indication is fixed), the chain piece between checked terminal connection and the battery means is serviceable. Continue check in the same spirit, serially passing from one terminal connection of a chain to another, moving in the direction from a battery/safety lock. The faulty site of a contour will settle down between a point on which the device will not register existence of tension and the next tested serviceable terminal connection. More often electroconducting break, or oxidation/weakening of fastening of a contact element appears a cause of failure.

Search of the reasons of short circuit

PERFORMANCE ORDER

First of all disconnect the consumer (and) the electric power of a checked contour (consumers of the electric power, or useful loading of a contour, components for which functioning the current circulating in a chain, such as lamps, electromotors, heating elements, etc. is spent are called) . Take the safety lock protecting the checked contour, and connect to its adjusting plugs a lamp sampler or the voltmeter. Submit power supply to a contour, - remember that some of contours запитываются only in certain positions of the switch of ignition. If tension on plugs of a safety lock takes place, therefore, in a chain there was a short circuit, - pull electroconducting as short circuit can be caused by destruction of its isolation and have unstable character. If tension is absent, however the safety lock after replacement continues to fuse when giving food in a chain, means, internal defect of the consumer (it) the electric power, the switch or electroconducting isolation takes place. Alternatively check can be made by means of an ohmmeter: disunite all contact sockets of the suspect of a site of a chain and, start to connect an ohmmeter between each of sockets and weight, registration by a measuring instrument of existence of conductivity (the zero indication) testifies to short circuit on mass of the electroconducting connected to the corresponding plug of the checked socket.

Search of violations of grounding

PERFORMANCE ORDER

The negative plug of the battery is earthed on "weight" as which metal of the power unit, the chassis and body elements of the car acts. Electric contours of the most part of electric equipment are constructed in such a manner that electroconducting is used only for food giving to the consumer from the positive plug of the battery, return of a current to the battery is carried out on weight metal. Told means that fixing elements of consumers of the electric power form themselves a returnable part of an electric chain. In view of the described situation, weakening of fastening or corrosion of basic elements of a working component of a chain involves violation of serviceability of functioning of a contour (from a full exit of the last out of operation before partial refusal of various sites of a chain). In particular, as a result of weakening of fixture brightness of a luminescence of lighting devices (in particular in the presence of the general grounding with other contour), or speed of rotation of the electromotor (for example, a drive of screen wipers or the fan of system of cooling) can decrease. Thus refusal of one contour can cause violation of functioning of the another which at first sight in any way has not been connected with failed. Pay attention that on many cars certain knots are connected among themselves by special tires of grounding. Such tires are used when there is no direct contact of metal parts of blocks in view of the equipment of support flexible rubber plugs (as, for example, in support of a suspension bracket of the power unit). For check of serviceability of grounding of a component disconnect the battery and connect one of ohmmeter wires to the obviously reliably earthed point of the car. The second wire of a measuring instrument connect to a point of grounding of a checked component. The device should fix zero resistance, otherwise it is necessary to check serviceability of electric connection (see further). In the presence of suspicions on violation of quality of terminal connection, disassemble contact knot of grounding and smooth out to pure metal interfaced surfaces of plugs. Try to remove completely all traces of corrosion and dirt, then scratch out a knife paint, achieving unequivocal contact of metal surfaces. At assembly of knot take care of durability of a tightening of fixture. Between plugs of electroconducting and weight contacts for a quality assurance of electric connection lay washers with a notch. In order to avoid corrosion development in the future cover the joined terminal connections by acid-free vaseline or silicone greasing. Good means are also an aerosol for sealing of components of system of ignition and water-repellent greasing.

Search of breaks of a chain

PERFORMANCE ORDER

Unstable refusals of consumers of the electric power appear connected with violation of quality of terminal connections at the expense of oxidation or weakening of fixture more often. Often for component reduction in a working condition, it appears to pull rather simply the corresponding plait of electroconducting / the electric socket. The simplest way of search of break of a chain is check of its working sites on conductivity existence. Disconnect power supply of a contour and use the equipped independent power supply a measuring instrument. Connect measuring instrument wires to both exits of a checked chain (the plug of giving of a food and well earthed point). If the device fixes conductivity existence (zero resistance/operation of a lamp sampler), therefore, the checked site of a chain is serviceable. Break otherwise takes place. By similar way serviceability of functioning of switches can be checked.

Electric sockets - general information

PERFORMANCE ORDER

The majority of contact sockets of chains of onboard electric equipment are made of plastic and are multicontact. Reliability of a joint of half of such sockets is provided with a zashchelkivaniye of lock uvulas of the clamps built in in tips. Large sockets, such as some from located under the car dashboard, are fastened passed through the central part of tips by through bolts more often. For a rassoyedineniye of the sockets equipped with plastic clamps the small screw-driver to which should wring out accurately lock uvulas (previously attentively usually is used study a design of the joined socket - often to measure a way of fixing of its half by eye not so simply; some sockets are equipped with several lock knots). Pull only for the tip, and at all for an electroconducting plait, in order to avoid casual damage of the contact plugs built in in the socket. Sockets always consist of two sections plugs of one of which enter in plugs another. When studying the schematic image of the socket try to define first of all which of its sections it is presented on an illustration, - connected to a plait, or fixed on a component. Remember that plugs of one section of the socket always are placed specularly in relation to plugs another. At conductivity stock-taking between plugs of the socket or tension measurement between any of plugs and "weight" always connect щупы a measuring instrument to plugs from the back (cordlike) party of the corresponding section of the socket. In case of need use щупы a tiny design, or enter into the socket the unbent writing paper clip to which then it is possible to connect a measuring instrument wire by means of a crocodile type clip. Tension measurement on contact plugs of the joined electric socket is made by introduction щупов a measuring instrument (1) in plugs from the back party of the tip; at a tight design of the socket the tester can be connected from the terminal party of the tip with the help щупов a tiny design (2) If the socket has a tight design, the measuring instrument can be connected from the terminal party of the socket, however, in such situation it is necessary to observe extra care in order to avoid damage of plugs.