15.1. Search of causes of failures of electric equipment
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The procedures described below 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 turning on electronic modules of management (ECU) in the structure. |
General information
The typical electric contour consists of the consumer of the electric power (a working component), switches of management (keys), the relay, driving electric motors, safety locks, fusible inserts / breakers of a chain concerning work of this component, and also connecting electrical wiring, its contact plugs and sockets. For the purpose of simplification of implementation of diagnostic procedures schemes of electric connections of various systems of electric equipment of the car are provided in the last section of this Chapter.
Before starting identification of causes of failure of the failed electric device, attentively study the corresponding electric circuit. Try as it is possible to imagine more clearly the principle of functioning of the components which are a part of this contour. The list of possible causes of failure can be minimized by an exception of it of unambiguously regularly functioning components concerning work of the checked chain. At simultaneous violation of functioning at once of several components or contours, failure of the general for these contours of a safety lock, or grounding violation is the most probable cause of refusal.
Most often failures of electric equipment are explained by the elementary reasons, such as oxidation or weakening of fastening of terminal connections, failure of a safety lock or 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, contact sockets and an electrical wiring. For definition of the list of the knots which are subject to check and terminal connections study the corresponding electric circuit (see Removal and installation of components of a safety cushion).
It is necessary to carry to number of the main tools necessary at search of failures of electric equipment:
a) The measuring instrument of a chain or the voltmeter (the usual 12-voltny lamp with a set of connecting wires will also be suitable for some checks);
b) A lamp sampler with the individual power supply (sometimes called also by the conductivity measuring instrument);
c) Ohmmeter;
d) Battery;
e) Set of connecting wires;
f) A set of the wires crossing points equipped various type with connecting plugs and, it is desirable, equipped with the breaker of a chain or a safety lock (for shunting of suspicious sites of a chain or electric components).
Before starting actually performance of checks, attentively study the corresponding Schemes of electric equipment.
The simplest check of a chain which is carried out by twitching of various sites of an electrical wiring of the corresponding contour can be made for search of the reason of the refusal having unstable character (refusals such usually are connected with oxidation or weakening of fastening of terminal connections). As a result of such check it is possible to localize a defective piece of a chain. This check can be made in addition to 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 circuit to number of the most probable and often found refusals of electric chains.
The break of a chain usually is defined by mechanical injury of conducting veins or a detachment of contact plugs that leads to disconnection of a contour and the termination of circulation in it electric current. As a result of break of a chain its working component ceases to function, however the corresponding safety locks / fusible inserts do not fail.
Short circuit is called unforeseen a chain design short circuit of its electrical wiring. At the same time current begins to circulate on the shortest way, usually leaving on weight. Short circuits are most often connected with violation of integrity of isolation of an electrical wiring and without fail lead to failure of safety locks / fusible inserts of protection of a chain.
Search of breaks of a chain
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Identification of the reasons of short circuit
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Identification of violations of grounding
The negative plug of the battery is grounded on the metal of the power unit, chassis and body elements of the car called by "weight". Electric contours of the most part of electric equipment are constructed in such a way that the connecting electrical wiring is used only for giving of power supply to the consumer from the positive plug of the battery, return of current to the battery is carried out on weight metal. It means that fasteners of consumers form themselves a returnable part of a chain. In view of the aforesaid, weakening of fastening or development of 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 of devices brightness of a luminescence of lighting fixtures (can decrease in particular at the general grounding with other contour) or the speed of rotation of an electric motor (for example, the drive of screen wipers or the fan of the cooling system). At the same time the refusal of one contour can cause violation of functioning of another, externally not connected with failed in any way. 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 elastic rubber pillows and plugs (as, for example, in support of fastening of the power unit to the car chassis).
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