13.2. Detection of not closed chain

The usual electric chain consists of an electric element, switches, the relay, engines, safety locks, automatic switches, wires and sockets which connect an electric element to the accumulator and a body. For the help by search of sources of malfunction of system of electric equipment in subsection 13.26 schemes of electric equipment of the car are provided.

Before trying to define a malfunction source, study the corresponding scheme of electric equipment for receiving idea of the elements established in this chain. The circle of possible sources of malfunction can be narrowed if to check functioning of other elements entering this chain. If several elements or chains fail at the same time, then the problem, obviously, consists in a safety lock, the general for these chains or elements, or contact with a body.

Electric problems are usually caused by the simple reasons, such as the weakened or rusted sockets, lack of contact with a body, the fused safety locks, the melted burned-through crossing point or the faulty relay. Visually check a condition of all safety locks, wires and sockets in the failed chain before starting check of other elements. Use schemes of electric equipment for definition of what of trailer clips need to be checked for detection of a source of malfunction.

The main tools necessary for detection of a source of malfunction, the tester or the voltmeter are (the bulb on 12 volts and couple of wires with probes on the ends can be also used for conducting some checks); ohmmeter; the battery and a set of wires with probes, a cap puncture, it is desirable with the automatic switch or a safety lock which is used for a round of the checked wires or elements.

For detection of the reason of unreliable work any of elements (usually because of bad connection or pollution of contacts, and also the damaged isolation) can carry out an inspection stirring of wires. It is necessary to shake a wire by a hand to check whether malfunction at the movement of a wire appears. By such method it is possible to narrow a circle of possible sources of malfunction to any wire.

Along with problems because of bad connection of wires two main types of malfunctions can take place in system of electric equipment – the opened chain or short circuit.

Problems with the opened chain appear as a result of break in electric equipment chain that interrupts course of current. The opened chain will cause shutdown of an element of electric equipment.

Problems with short circuit are caused by short circuit of the site of a chain that leads to leakage of current from other chain, usually directly on a body. Short circuit is usually caused by a rupture of isolation of wires that allows a wire to concern other wire or any grounded element, for example, of a body. Short circuit usually leads to burn-out of the corresponding safety lock.

Detection of a rupture of a chain

1. For check of integrity of a chain connect the device for verification of schemes or the negative probe of the voltmeter to the negative plug of the accumulator or the grounded element.
2. Connect the second probe to connection in the checked chain, it is desirable for the next to the accumulator or a safety lock. At the same time this site of a chain has to be energized from the accumulator if only the socket of connection to the accumulator does not carry current or the safety lock did not fuse (at the same time do not forget that some chains of electric equipment join only at turn of a key in the ignition lock in a certain situation).
3. Include a chain, then connect the tester probe to connection, the next to the chain switch on the party of the checked element.
4. If tension is present (what the control bulb or indications of the voltmeter testifies to), it means that the site of a chain between the corresponding connection and the switch has no gaps.
5. Continue check of a chain in the same way. If the site on which there is no tension is found, it means that the rupture of a chain occurred between this point and a point of the previous check on which there was tension. The majority of problems of the opened chain are caused by the broken or weakened socket.

Detection of a source of short circuit

1. For detection of a source of short circuit disconnect chain loading elements in the beginning (elements of loading of a chain are elements which consume electric current, such as bulbs, electric motors, heating elements, etc.).
2. Remove the corresponding safety lock and connect probes of a tester or the voltmeter to safety lock plugs.
3. Include food in chains, at the same time do not forget that some chains of electric equipment join only at turn of a key in the ignition lock in a certain situation.
4. If tension is present (what the control bulb or indications of the voltmeter testifies to), it means that in a chain there is a short circuit.
5. If when conducting check there is no tension, however the safety lock still fuses at connection of that loading of a chain, it demonstrates failure of an element of loading.

Detection of bad grounding

The negative plug of the accumulator is connected to "weight" – metal of a body, the engine or transmission. At the same time many elements of electric equipment are connected in such a way that only the positive wire approaches them, at the same time current comes back to the accumulator through body metal. It means that fastening of an element of electric equipment and a body are a part of an electric chain. Thereof the bad or rusted fastening can cause failure in the functioning of an element or lead to its unstable or bad work. In particular, bulbs can burn with dim light (especially if in a point of grounding of this bulb grounding any else the switched-on electric equipment element is carried out), electric motors can slowly work, and also work of one chain can have effect imperceptible at first sight on work of other chain. Do not forget that on many cars grounding wires between some elements, such as the engine, transmission and a body are used, that is in those places where there is no direct contact between metal elements because of soft rubber fastenings or a paint coat.

1. For check of reliability of grounding of an element it is necessary to switch-off the accumulator and to connect one of ohmmeter probes to reliably grounded element. Connect other probe to a wire or connection with a body which needs to be checked. Resistance shown by an ohmmeter has to be equal to zero; if is not present, check connection as follows.
2. If you assume lack of grounding, investigate connection and clear the site of a body and the plug of a wire (or the surface of grounding of an element) to pure metal. Carefully remove all traces of dirt, then by means of a knife peel all paint so that the reliable contact of two metal surfaces turned out. At assembly reliably delay fastening of the socket; at connection of the plug of a wire establish a washer with rough edges between the plug and a surface of a body for ensuring reliable connection. At connection prevent emergence of corrosion in the future, having put a layer of vaseline or silicone lubricant.