Note: Please read the cautions in the safety paragraph and in paragraph 1 this chapter. The procedures described in this chapter apply only to the main electrical circuits and should not be used to test the electronic circuits of systems (such as anti-lock braking system), and especially those used by electronic control units.
General information
1. A typical electrical circuit contains some electrical component, switches, relays, motors, fuses, fuses, or circuit breakers associated with that component, as well as wiring and connectors that connect the component to the battery and chassis. To assist in troubleshooting electrical circuits, wiring diagrams are provided at the end of this manual.
2. Before troubleshooting an electrical circuit, study the appropriate wiring diagram and get a complete understanding of the components included in this circuit. The search for possible sources of malfunction is easier if you make sure that other components included in this circuit are working. If several components or circuits fail at the same time, the fault may be due to their common fuse or ground connection.
3. Malfunctions in electrical circuits usually occur due to simple causes, such as: loose or corroded connections, unreliable grounding, fuse or fuse failure, or a relay malfunction (see paragraph 3 for a detailed description of the relay test). Before you begin checking circuit details, inspect the condition of all fuses, wires, and connectors in the faulty circuit. Use the wiring diagrams to determine which connections you need to check to pinpoint the location of the problem.
4. The list of basic tools for troubleshooting electrical circuits contains a tester or voltmeter (for some tests, a 12-volt bulb with test leads may also be used); battery powered indicator (also called break indicator); ohmmeter (for measuring resistance); battery with a set of wires for control; jumper wire, preferably with a fuse, which can be used to bypass wires or electrical components under test. Before you start troubleshooting with the help of devices, determine the points for their connection according to the wiring diagram.
5. To find the source of an intermittent wiring fault (usually caused by a bad connection, or damaged wiring insulation), you can just move the wires. If at the same time the contact in the circuit either appears or disappears, then the source of the malfunction is located in this place of the wiring. This verification method may be used along with any of the others described in the following subparagraphs.
6. In addition to bad contacts, there are two more main types of malfunction: open circuit and short circuit.
7. If the circuit breaks in any of its places, the current supply to the component stops and, as a result, its operation, although the break in the circuit does not lead to failure of the fuse.
8. A short circuit is usually caused by a violation of the insulation of the electrical wiring when there is a mutual contact of the wires or the wire with the case. A short circuit usually destroys the fuse in the corresponding circuit.
Open Circuit Detection
9. To test for an open circuit, connect one of the tester's terminals or the negative terminal of a voltmeter to the negative battery terminal or to a good ground.
10. Connect the other tester terminal to a connector on the circuit under test, preferably one closest to the battery or fuse.
11. Turn on the circuit, then connect the tester terminal at the location closest to the area under test. Note that some circuits are only closed when the ignition switch is in a certain position.
12. Presence of voltage (as evidenced by the light of the control light or voltmeter readings), means that the circuit line between the corresponding connector and the battery is good.
13. Continue checking the rest of the circuit in the same way.
14. If the point at which there is no voltage is found, then the section between this point and the previous checked point is faulty. Check it to find a problem. Most failures are caused by corrosion, broken or loose contacts.
Circuit short detection
15. Before checking the circuit for a short circuit, disconnect the load from the circuit (load - components that consume power, such as light bulbs, motors, heating elements, etc.).
16. Remove the appropriate circuit fuse and connect the tester or voltmeter wires to its terminals.
17. Turn on the circuit, bearing in mind that some circuits are closed only when the ignition switch is in a certain position.
18. Presence of tension (as evidenced by the light of the control light or voltmeter readings) confirms a short circuit.
19. If no voltage is present during this test, but the fuse blows when the load is connected, this indicates an internal fault in the load.
Ground Fault Detection
20. The negative battery terminal is connected to "grounding" - engine-transmission-body block. Only the positive wire is suitable for most consumers of electricity, and the metal of the body is the negative conductor. This means that the body mass is part of the chain. In this regard, loose connections can lead to partial or complete breakage of the chain. And this can cause a dim glow of lighting devices (especially if another circuit is switched on using the same ground point), deceleration of motor rotation (such as a wiper motor or a cooling fan motor) and the influence of one circuit on the operation of another. Note that many vehicles use flexible ground straps to connect to the body of units that do not have direct metal contact with it, such as an engine-transmission unit mounted on rubber pads.
21. To check if the component is properly grounded, disconnect the battery and connect one ohmmeter lead to a good ground. Connect the second wire of the ohmmeter to the component to be tested. The ohmmeter should register zero resistance; otherwise, check the component ground connection as follows.
22. If you suspect that the ground connection is broken, disassemble this connection, clean both the contact point on the body and the wire tip (or mounting surface of the assembly housing) to metal. Remove all traces of dirt and corrosion, scrape off the paint with a knife. to ensure a clean metal-to-metal connection. Assemble the connection and carefully tighten the fasteners. If the wire ends have lugs, install serrated washers between the lugs and the housing to ensure a secure connection. In order to prevent corrosion of the connection after restoration, lubricate it from the outside with technical vaseline or silicone grease (or periodically spray on it with special moisture-protective agents).
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