12.2. Search of causes of failures of an electric equipment
Described below procedure allow to make the general diagnostics of a condition of the main electric contours, however should not be applied to check of electric systems open to injury (such as, for example, ABS), in particular, including in the structure electronic modules of management (ECM).
The typical electric contour consists of the electric power consumer (a working component), a set of switches, the relay, executive electromotors, safety locks, the fusible inserts / of breakers of the chain concerning work of the given component, and also connecting electroconducting, its contact plugs and sockets. For the purpose of simplification of performance of diagnostic procedures in last section of the present Chapter schemes of electric connections of various systems of an electric equipment of the car are resulted.
The general information
Before to start search of causes of a failure of the failed consumer of the electric power, attentively study the corresponding electric scheme, try as it is possible to imagine more clearly a principle of functioning of the components which are a part of the suspected contour. The list of possible causes of a failure can be shown to a minimum by an exception of it of regularly functioning components concerning work of the checked contour. At simultaneous infringement of functioning at once several components, most a refusal plausible reason is failure of the general for corresponding chains of a safety lock / of a fusible insert, or grounding infringement.
More often electric equipment refusals speak the elementary reasons, such as damage by corrosion, or fastening easing клеммных connections, failure of a safety lock or a fusible insert, relay refusal, etc. Before to start search of internal defects of actually refused component, attentively check up a condition of all safety locks concerning its functioning, sockets and connecting wires.
For definition of the list of knots subject to check and клеммных connections, study the corresponding scheme of electric connections.
To number of the diagnostic equipment necessary by search of refusals of an electric equipment, it is necessary to carry a universal measuring instrument of a chain / the voltmeter (for some checks 12-voltnaja the lamp with the complete set of connecting wires also will approach), a lamp-sampler with the individual power supply (sometimes named also a conductivity measuring instrument), an ohmmeter, the power supply with the complete set of connecting wires, and also a set of the wires-crosspieces, 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 to resort to use of the diagnostic equipment attentively study the scheme of electric connections of components of a corresponding contour.
The elementary check of a chain which are carried out by twitching of various sites of electroconducting of the corresponding contour in which result the defective piece of a chain is localised can be made for search of the reason of refusal having astable character (infringements such usually appear connected with oxidation of contact plugs, or fastening easing клеммных electroconducting connections). The given check can be made together with any of listed more low in corresponding subsections.
Except the problems connected with infringement of quality of electric connections, it is necessary to carry breakages and short circuits to number of the most probable and often occurring refusals of electric contours in a chain.
Chain breakage is usually caused by mechanical damage токопроводных veins or a detachment of contact plugs that leads to disconnection of an electric contour and the circulation termination in it of an electric current. As a result of chain breakage its working component ceases to function, however corresponding safety locks / fusible inserts do not fail.
As short circuit is called unforeseen a design of a chain short circuit of its electroconducting. Thus the current starts to circulate on the shortest way, usually leaving on weight. Short circuits appear connected with infringement of integrity of isolation of electroconducting more often and without fail lead to failure of corresponding safety locks / of fusible inserts.
Pressure stock-taking in a chain
Pressure stock-taking is included into number of standard checks in default any consumer of the electric power. Connect one of wires of a measuring instrument of a chain or the voltmeter to the negative plug of the battery, or any of reliably earthed points on the chassis / the car engine. The second wire of the device connect to клеммному to connection of a checked contour, it is preferable to the nearest 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 pressure takes place (the measuring instrument lamp joins, or on the voltmeter indicator the corresponding indication is fixed), the chain piece between checked клеммным connection and the battery means is serviceable.
Continue check in the same spirit, serially passing from one клеммного chain connections to another, moving to a direction from the safety lock battery/. The faulty site of a contour will settle down between a point on which the device will not register presence of pressure both previous tested and serviceable клеммным connection. More often electroconducting breakage, or oxidation / fastening easing клеммного connections appears a cause of a failure.
Search of the reasons of short circuit
First of all disconnect the consumer () the electric power of a checked contour (electric power consumers, 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 supplies to a contour. Remember that some of contours запитываются only in certain positions of the switch of ignition. If pressure takes place on safety lock plugs, hence, in a chain there was a short circuit (pull electroconducting as short circuit can be caused wiping of its isolation and have astable character). If pressure is absent, however the safety lock after replacement continues to fuse at food giving in a chain, means, internal defect of the consumer (it) the electric power, the switch or electroconducting isolation takes place.
Search of infringements of grounding
The negative plug of the battery is earthed on "weight" in which quality metal of the power unit, the chassis and кузовных car elements acts. Electric contours большей electric equipment parts 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, easing of fastening or corrosion of basic elements of a working component of a chain involves infringement 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 fixture easing 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 infringement of functioning of the another which outwardly in any way have been not connected with failed. Pay attention that on many cars certain knots are connected among themselves by special tyres of grounding. Such tyres 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 fastening of the power unit to the car chassis).
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 up serviceability of connection (see further).
In the presence of suspicions on quality infringement клеммного connections, disassemble contact knot of grounding and smooth out to pure metal interfaced surfaces of plugs. Try to remove completely all traces of corrosion and a dirt, then scratch out a knife a paint, achieving unequivocal contact of metal surfaces. At knot assemblage take care of durability of a tightening of fixture. Between plugs of electroconducting and weight contacts, for the quality assurance of electric connection, lay washers with a notch. In order to avoid corrosion development in the future cover joined клеммные connections бескислотным with vaseline or silicone greasing. Good means are also an aerosol for hermetic sealing of components of system of ignition and water-repellent greasing.
Search of breakages of a chain
Astable refusals of consumers of the electric power appear connected with quality infringement клеммных connections at the expense of oxidation or fixture easing more often. Often for component reduction in a working condition, it appears to pull simply enough a corresponding plait of electroconducting / an electric socket. The most simple way of search of breakage of a chain is check of its working sites on conductivity presence. Disconnect power supplies of a contour and take advantage of 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 presence (zero resistance / lamp-sampler operation), hence, the checked site of a chain is serviceable. Breakage otherwise takes place. In the similar way serviceability of functioning of switches can be checked up.