Circuit fault detection
A typical electrical circuit consists of an electrical element, switches, relays, motors, fuses, circuit breakers, wires and connectors that connect the electrical element to the battery and body. To assist in troubleshooting the electrical system, the manual provides wiring diagrams for the vehicle.
Before attempting to determine the source of a fault, study the relevant circuit diagram to get an idea of the elements in this circuit. The number of possible sources of malfunction can be reduced by checking the operation of other elements included in this circuit. If several elements or circuits fail at the same time, the fuse common to these circuits or elements may be defective, or the connection to the body is broken - «weight».
The causes of the malfunction are loose or oxidized connectors, poor contact with the body, blown fuses or faulty relays. Visually check the condition of all fuses, wires and connectors in the failed circuit before proceeding to check the rest of the elements. Use wiring diagrams to identify potential fault points that need to be checked to locate the source of the fault.
The main instruments needed to locate the source of a malfunction are a tester or voltmeter, a 12 V test lamp, an ohmmeter, a battery and a set of wires with probes, a captive puncture, preferably with a circuit breaker or fuse, which is used to bypass the tested wires or elements.
In addition to a bad wire connection in an electrical system, there are two more main types of faults - an open circuit or a short circuit.
The circuit opens as a result of an open circuit in the electrical equipment, which interrupts the current, causing the electrical equipment to turn off.
To test continuity, connect a circuit tester or voltmeter, one lead to the negative battery terminal or ground, and the other to a terminal in the circuit under test, preferably one that is closest to the battery or fuse. In this case, the tested section of the circuit must be energized from the battery, except for the case when the connection to the battery does not conduct current or the fuse is blown (do not forget that some electrical circuits are switched on only when the key in the ignition switch is turned to a certain position).
Turn on the circuit, then connect the tester probe to the connection closest to the circuit breaker on the side of the item being tested.
If there is tension (as evidenced by the ignition of the control lamp or voltmeter readings), which means that there are no breaks in the section of the circuit between the corresponding connection and the switch.
If a section is found where there is no voltage, then an open circuit occurred between this point and the point of the previous test, which had voltage. An open circuit is caused by a damaged or loose connector.
Possible sources of a short circuit can be the following consumers of electricity: lamps, electric motors, heating elements, etc.
Remove the appropriate fuse and connect the tester or voltmeter leads to the fuse terminals.
Turn on the power in the circuit, while not forgetting that some circuits of electrical equipment are turned on only when the key in the ignition switch is turned to a certain position.
If there is voltage in the circuit, then a short circuit has occurred in the circuit.
The negative terminal of the battery is connected to «mass» - body, engine or gearbox. An insecure or oxidized fastening may cause the element to fail or malfunction. Do not forget that many cars use «massive» wires between some elements, such as an engine, transmission with a body, that is, in those places where there is no direct contact between metal elements due to soft rubber mounts or a layer of paint.
To check the reliability of the grounding of the cell, disconnect the battery and connect one of the ohmmeter leads to a reliably grounded cell. Connect the other lead to the wire or body connection to be tested. The resistance shown by the ohmmeter should be zero, if not, then check the connection as follows: if the reliability of contact with «weight», then disassemble the connection, remove dirt and clean the contacts. When reassembling, tighten the connector retainer by applying a coat of petroleum jelly or silicone grease to prevent corrosion.