Skoda Felicia

since 1994 release

Repair and operation of the car

Search of causes of failures of electric equipment

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, 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 at the end of this Chapter schemes of electric connections of various systems of electric equipment of the car are provided.

Before starting troubleshooting 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 (the description of procedures of check of an isprvnost of functioning of the relay is provided in the Section Safety locks, the relay and breakers - the general information), etc. Before starting search of internal defects of actually refused component, attentively check a condition of all safety locks concerning its functioning, sockets and wires. For definition of the list of the knots which are subject to check and terminal connections study the corresponding electric circuit.

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 corresponding (from provided in the end of the present Chapter) schemes of electric connections.

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 (violations such usually are connected with oxidation or weakening of fastening of terminal connections of an electrical wiring). As a result of such manipulations often it is possible to localize a defective piece of a chain. 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 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 usually connected with violation of integrity of isolation of an electrical wiring and without fail lead to failure of safety locks / fusible inserts of a chain.

Search of breaks of a chain

For check of a contour on break connect one of wires of the measuring instrument of a chain or the voltmeter to the negative plug of the battery or any of reliably grounded points on the chassis or the engine of the car.

Connect the second wire of the device to terminal connection of the checked contour, preferably, to the next to the battery or a safety lock.

Include food - do not forget that some of contours are powered only in certain provisions 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 the checked terminal connection and the battery means it is serviceable.

Continue check, 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 lie between a point on which the device will not register presence of tension and the last of the checked correct terminal connections. Most often the break of an electrical wiring, or oxidation/weakening of fastening of the plug appears a cause of infringement.

Search of the reasons of short circuit

First of all disconnect the consumer(s) of the electric power of the checked contour (consumers of the electric power, or the payload of a contour are called components for which functioning the main share of energy of the current circulating in a chain, such as lamps, electric motors, heating elements, etc. is spent).

Take a safety lock of protection of the checked contour and connect the measuring instrument of a chain or the voltmeter to its adjusting plugs.

Include food - you remember that some of contours are powered only in certain provisions of the switch of ignition.

If tension takes place on safety lock plugs, so in a chain short circuit takes place.

If tension is absent, however the safety lock still fuses when giving food in a chain, therefore internal defect of the consumer(s) of the electric power of a contour takes place.

Search 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 of the electric power 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 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 (such as, in support of a suspension bracket of the power unit).

For check of serviceability of grounding of a component switch-off the battery and connect one of ohmmeter wires to obviously reliably grounded point of the chassis or power unit. Connect the second wire of the measuring instrument to a point of grounding of the checked component. The device has to record zero resistance, otherwise it is necessary to check serviceability of connection.

In the presence of suspicions on violation of quality of terminal connection of grounding, sort contact knot and smooth out the interfaced surfaces of plugs to naked metal. Try to remove completely all traces of corrosion and dirt, then scratch out a knife paint, trying to obtain unambiguous contact of metal surfaces. At assembly of knot take care of durability of tightening of fixture. Between plugs of an electrical wiring and contacts of weight, for a quality assurance of electric connection, lay washers with a notch. In order to avoid corrosion development in the future cover the connected terminal knots with acid-free vaseline or silicone lubricant. Good means are also the aerosol, the applied to sealing of components of system of ignition and water-repellent lubricant.