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Search of causes of failures of electrical equipment
 | These procedures permit a common diagnosis of the main electric circuit, but should not be used to verify the already fragile electrical systems (such as, for example, ABS), in particular, includes in its membership the electronic control module (PCM). |
Overview
A typical electric circuit consists of a power consumer (operating component), a set of switches, relays, actuators of electric motors, fuses, fuse links / circuit breakers, relevant to the work of the component, and the connective wiring, its contact plugs and connectors. In order to facilitate the implementation of diagnostic procedures in the last section of this chapter shows the wiring diagrams of different systems of electric vehicles.
Before embarking on the search for the causes of failure of the failed consumer of electricity, carefully read the corresponding circuitry as clearly as possible, try to imagine the principle of operation of the components that make up the suspect circuit. The list of possible causes of failure can be minimized by delisting properly functioning components related to the circuit under test. With the simultaneous operation of multiple violations of the components, the most likely cause of failure is the failure of the total for the corresponding circuit fuse / fuse or a ground fault.
The most common electrical failure is easily explained reasons, such as damage by corrosion or loose terminal connections, the failure of the fuse or the fuse, failure relays, etc. Before embarking on the search for internal defects actually failed component, carefully check the condition of all relating to his operation of fuses, connectors and connecting wires.
To determine the list of sites to be inspected and terminal connections, please read the appropriate wiring diagram.
Among the diagnostic equipment needed when searching for electrical failures, should include a universal measuring circuit / voltmeter (for some tests and fit 12-volt bulb with a set of connecting cables), bulb-probe with individual power supply (sometimes also referred to as conductivity meter), ohmmeter , a power supply with a set of connecting cables, as well as a set of jumper cables, equipped with various types of connection terminals and, preferably, a built-in circuit breaker or fuse (to bypass the chain of suspicious areas or electrical components). Before resorting to the use of diagnostic equipment, read the wiring diagram components of a circuit).
To find the causes of the wearer's unstable failure (violations of this kind are usually associated with the oxidation of contact plugs, or loose terminal connections wiring) can be made simple test circuit performed by twitching of various parts of the wiring of the corresponding circuit, which resulted in localized defective segment of the chain. This check can be performed in conjunction with any of the following in the respective sections.
In addition to the problems associated with the violation of the quality of the electrical connections to the most frequently occurring and the likely failure of electric circuits should include breaks and short-circuit.
Open circuit typically caused by mechanical damage to the electrically conductive cores or disconnecting the terminals, resulting in the opening of the electric circuit and stop the circulation of electric current therein. As a result, open-circuit component of its work ceases to function, however, appropriate fuses / fuse-links do not fail.
Short circuit design called an unintended closure of its electrical circuit. This current begins to circulate through the shortest path, usually takes on the weight. Short circuits are mostly related to the violation of the integrity of the insulation of the wiring in the mandatory lead to failure of the relevant fuse / fuse-links.
Check presence of voltage in the circuit
Checking tension among the standard tests in the event of any consumer of electricity. Connect one wire from the meter circuit or a voltmeter to the negative terminal of the battery, or any of properly grounded outlets on the chassis / engine. The second wire unit is connected to terminal connections checked the circuit, preferably closest to the battery or fuse. Apply power to the circuit. Do not forget that some chains are supplied only in certain positions of the ignition switch. If the voltage occurs (light meter is activated, or the display is fixed corresponding to the reading of the voltmeter), then cut the connection between the inspected terminal connection and the battery is OK.
Continue to check in the same spirit, alternately moving from one terminal to another circuit connection in the direction of the battery / fuse. The faulty section of the circuit will be located between the point at which the instrument registers the presence of voltage and the previous tried and serviceable terminal connection. The most common cause of failure is broken wiring or oxidation / loose terminal connections.
Search the short-circuit
Firstly disconnect the customer (s) under test electric circuit (power consumers or payload circuit are called components on the functioning of which is spent the circulating current in the circuit, such as lamps, electric motors, heating elements, etc.). Remove the fuse that protects the circuit under test, and connect it to the mounting terminals bulb-probe or voltmeter. Apply power to the circuit. Remember that some of the circuits are supplied only in certain positions of the ignition switch. If the voltage at the terminals occurs fuse hence the circuit is shorted (tug wiring as short circuit may be caused by wiping its insulation and wear unstable). If pressure is absent, however, after replacing the fuse continues to blow when power is applied to the circuit, so there is a defect in the internal user (s) of electricity, switch or wiring insulation.
Search disorders Ground
The negative terminal of the battery is grounded in the "mass", which serves as a metal powertrain, chassis and car body elements. Electrically mostly electrical circuits are constructed in such a way that the wiring is only used to supply power to the consumer from the positive terminal of the battery, the current returns to the battery is carried on the metal mass. This means that the fixings power consumers forming part of a return circuit. In view of this situation, loose or corroded support members of the working circuit component entails a violation of serviceability of functioning of the circuit (from the most recent complete failure to partial failure of various parts of the chain). In particular, due to the weakening of fasteners can decrease the brightness of lighting (in particular with a common ground with the other loop), or the rotation speed of the motor (for example, a drive wiper or cooling fan). At the same time the failure of one circuit can cause malfunction of another, apparently unrelated to the failed. Please note that on many cars some nodes are interconnected by special buses ground. Such tires are used in cases where there is no direct contact of the metal parts of the unit due to hardware supports flexible rubber bushings (as, for example, supports mounting power unit to the vehicle chassis).
To check the health of the ground component, disconnect the battery and connect one ohmmeter lead obviously a properly grounded point of the car. The second wire gauge to connect the grounding point under test component. The device should fix the zero resistance, otherwise check the faulty connection.
If there is suspicion of violation of the quality of the connection terminal, disassemble the contact assembly ground and smooth out to pure metal mating surfaces of the terminals. Try to completely remove all traces of corrosion and dirt, and then scrape off the paint with a knife, ensuring unambiguous contact metal surfaces. When assembling the unit, take care of the strength of a tightening of fixture. Between terminals and electrical contacts mass, to ensure the quality of the electrical connection, lay the washer with a notch. In order to avoid corrosion development in the future, cover the docked terminal connections with acid-free Vaseline or silicone grease. Good agents are also spray to seal the components of the ignition system and moisture repellent grease.
Search continuity
Unstable failures electricity consumers are most likely to involve a violation of the quality of terminal connections due to oxidation or loosening of fasteners. Often cast component in working condition, is simply to pull the appropriate wiring harness / electrical connector. The easiest way to find an open circuit is to check its working areas for the presence of conduction. Disconnect the power supply circuit and use equipped with autonomous power source meter. Connect the meter to the two outputs of the circuit under test (power supply terminal and a good ground point). If the device detects the presence of conductivity (zero resistance / operation of the lamp-sampler), therefore, the circuit under test plot is serviceable. Otherwise, there is a break. Similarly, the same method can be checked up serviceability of functioning of the circuit breakers.
Electrical connection - general information
Most of the pin connectors onboard electric circuits are made of plastic and are multicontact. Reliability joint halves of the connectors is provided by snap-locking tabs mounted in the plug latches. Large connectors, such as some of the located under the dashboard of a vehicle, often bonded is passed through a central portion of the plug through bolts.
To disconnect equipped with plastic clip connector is usually used a small screwdriver, which should be carefully squeeze locking tabs (after carefully review the design mated connector - often determine the method of fixing his eyes on the halves is not easy, and some connectors are equipped with multiple locking units). Always pull the plug, but in any case not at the wiring harness, to prevent accidental damage to the connector mounted in the terminals.
Connectors always consist of two halves, one of which terminals includes terminals inside the other. In the study of schematic images of connectors try to first determine which of its halves is represented by the illustration - connected to a harness or attached to the component. Remember that one half of the connector terminal is always placed a mirror in relation to the other terminals.
 | Often, the diagnosis of failures of electrical circuits is necessary to check the voltage at the terminals mated connector. In such tests the probe gauge inserted in the corresponding terminals on the rear side of the plug. Be careful, try not to bend or deform the terminal. If the socket terminal is too small, use as a metal probe straightened paper clip, to which you can then connect the wire with the clamp meter crocodile. |
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