14.2. Detection of malfunctions
Read about precautionary measures (see section 14) before the work beginning.
The following tests are intended for check of the main electric chains and they should not be used for check of sensitive electric chains (such as the ABS system), especially in case in a chain is the electronic operating block.
The typical electric chain consists of an element of electric equipment, switches, the relay, engines, the safety locks, 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. To simplify troubleshooting process, electric circuits of system of electric equipment of the car are given in subsection 14.20.
Before the beginning of check of a faulty chain, in the beginning study the schematic diagram of this chain to understand from what elements it consists.
The source of malfunction can be found quicker if to define, what of elements of this chain work normally.
If some elements or chains fail at once, the problem, possibly, consists in the fused safety lock or bad grounding as often one safety lock is responsible for some 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 (the description of operation of check of the relay see in subsection 14.3).
Visually check a condition of all safety locks, wires and connections in a faulty chain before the beginning of check of other elements of this chain.
If you are going to use instrumentations, use schematic diagrams to define, what connections are necessary for checking for failure detection.
The main devices necessary for search of malfunction in a chain of electric equipment, are the voltmeter (or a bulb on 12 Volts with connecting wires), the device for check of integrity of chains, an ohmmeter (for resistance measurement), the accumulator with connecting wires and a cap wire, it is desirable with the automatic switch which can be used for parallel connection to a chain.
Before the beginning of 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) it is possible to shake wires by a hand to see, whether there is a chain out of operation at wire movement. 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 – gap existence in a chain or short circuit.
The gap in a chain can be caused by a rupture of any wire or absence of connection somewhere in a chain that will prevent a current current. The gap in a chain will cause refusal of any element of electric equipment in work, but will not lead to a peregoraniye 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 that the current flowing on a chains, begins a leak on other chain, and more often, leaves on (weight). Short circuit is usually caused by a rupture of isolation that allows a feeding wire to concern either other wire, or the earthed element, such, as a body. Short circuit leads to a peregoraniye of a safety lock of the corresponding chain.