12.1.2. Search of malfunctions
The consumer, the switches, the relay and wires connected according to the enclosed scheme are a part of electric chains of the car. Before starting troubleshooting it is necessary to study the scheme and to define a possible source of malfunction. For example, the problem of troubleshooting is considerably facilitated if it is possible to check serviceability of other consumers directly or indirectly connected to the suspected chain.
If the refusal of several consumers is observed, then the break of connection with weight or burn-out of a safety lock is the most probable cause. As a rule failures of electric equipment are caused by weakening of contacts or their corrosion, burn-out of a safety lock or an oplavleniye of a crossing point. Search of malfunctions as a rule is carried out visually, and also by means of a tester (voltmeter) or a control lamp which are connected between the site of a faulty chain and well smoothed out weight.
Search of a source of malfunction in system of electric equipment
The typical electric chain consists of an element of electric equipment, switches, the relay, engines, safety locks, the burned-through crossing points or automatic switches and wires and connections which connect all elements among themselves and connect them to the accumulator and mass of the car.
Before check of a faulty chain, study the schematic diagram of this chain in the beginning to understand of what elements it consists. The source of malfunction can be found quicker if to define what of elements of this chain work normally. If several elements or chains fail at once, the problem probably consists in the fused safety lock or bad grounding as often one safety lock is responsible for several chains.
Problems with work of system of electric equipment are usually caused by the simple reasons, such as the oxidized or unreliable contacts, the fused safety lock, the fused burned-through crossing point or the faulty relay. Visually check a condition of all safety locks, wires and connections in a faulty chain before check of other elements of this chain. If you are going to use instrumentations, use schematic diagrams to define what connections need to be checked for failure detection.
4. The main devices necessary for search of malfunction in electric equipment chain, are:
a) the device for verification of schemes or the voltmeter (or a bulb on 12 Volts with connecting wires);
b) a control bulb with the power supply (or the device for check of integrity of chains);
c) an ohmmeter (for measurement of resistance);
d) accumulator;
e) probes with wires;
e) a cap wire, it is desirable with the automatic switch or a safety lock which can be used for check of wires or elements of electric equipment.
Before search of malfunction with use of the control and measuring equipment, study schematic diagrams to define connection points.
For search of unreliable connection or a point of short circuit (usually because of the bad or polluted connection, or the damaged isolation) wires can be shaken by a hand to see whether the chain fails at the movement of a wire. In such way it is possible to find a point with unreliable connection or a point in which there is a short circuit. This method of check can be used along with other tests described in the following subsections.
Besides the problems connected with bad connection, the electric chain can have two other main malfunctions – existence of a gap in a chain or short circuit.
The gap in a chain can be caused by a rupture of any wire or lack of connection somewhere in a chain that will prevent a current of current. The gap in a chain will cause refusal of any element of electric equipment in work, but will not lead to burn-out of a safety lock of this chain.
The malfunctions connected with short circuit are caused by short circuit somewhere in a chain that leads to the fact that the current flowing on a chain begins to flow on other chain, and most often, leaves on weight. Short circuit is usually caused by a rupture of isolation that allows the feeding wire to concern either other wire, or the grounded element, such as a body. Short circuit leads to burn-out of a safety lock of the corresponding chain.
Before search of a source of malfunction or when carrying out repair in system of electric equipment, do not forget that various types of wires have various color.
Search of a rupture of a chain
For search of a rupture of a chain connect one of probes of a control bulb to the negative plug of the accumulator or mass of the car.
Connect the second probe to connection in the checked chain, it is desirable located as it is possible closer to the accumulator or a safety lock.
Give tension on a chain. Do not forget that tension is only present at some chains if to turn a key in the ignition lock in a certain situation.
If tension is present (what the lit-up control bulb or indications of the voltmeter will testify to), it means that a part of a chain between connection and the accumulator is serviceable.
Continue check of other part of a chain in the same way.
When you find a point where tension is absent, it means that the source of malfunction lies between this point and the last point where tension was present. The majority of problems is caused by bad connection.
Search of short circuit
For check of a chain on existence of short circuit, disconnect chain loading in the beginning (loading is elements of electric equipment which consume the electric power, such as bulbs, engines, heating elements etc.).
Remove a safety lock of the corresponding chain and connect a control bulb or the voltmeter to plugs of connection of a safety lock.
Give tension on a chain. Do not forget that tension is only present at some chains if to turn a key in the ignition lock in a certain situation.
If tension is present (what the lit-up control bulb or indications of the voltmeter will testify to), it means that in a chain there is a short circuit.
If there is no tension, but the safety lock nevertheless fuses at connection of elements of loading, so is faulty any of these elements.
Check of reliability of grounding
The negative plug of the accumulator is connected to the mass of the car – to metal of the engine / transmission and a body of the car – and the majority of systems of electric equipment are developed so that one feeding wire approached an element of electric equipment only, and current came back through car body metal. It means that fastening of an element of electric equipment and a body of the car are a part of an electric chain. Therefore, the bad or oxidized fastening can be the reason of a large number of malfunctions in system of electric equipment, from a full exit of a chain out of operation before its unreliable work. In particular, bulbs can dimly burn (especially if other chain using the same grounding is included), engines (for example, engines of screen wipers or the fan of cooling of a radiator) can slowly work and inclusion of any chain can influence work of other chain. Notice that on many cars the connecting grounding strips between various units of the car, for example, between the engine/transmission and a body are used, usually when between elements there is no metal contact because of use of rubber fastenings etc.
For check of reliability of grounding disconnect the accumulator and connect one of ohmmeter probes to the mass of the car. Connect the second probe to a wire or a point of grounding which needs to be checked. Resistance registered by an ohmmeter has to equal to zero; if is not present, check connection as follows.
If you consider that connection not as it should be, investigate connection and smooth out a contact surface and the plug of a wire or a surface of the grounded element to pure metal. Remove completely dirt and traces of corrosion, then, by means of a knife remove a paint coat to receive reliable compound of metal with metal. At assembly, reliably record connection; at installation of the plug of a wire, use gear washers between the plug and a body. After connection, for prevention of formation of corrosion apply a layer of vaseline or silicone lubricant on connection.
Sockets
On the considered cars multicontact sockets with plastic cases are used. Reciprocal parts of sockets are kept by latches or the central screw (for example in sockets under the dashboard).
| Latches are uncoupled by the thin flat tool. In some sockets of latches can be more than two. For check of a chain without socket detachment probes of the device are entered from the socket back against the stop into the plug. |