Contents: General information ↳ Detecting chain breaks ↳ Short circuit detection ↳ Ground fault detection ↳
Note: Before you begin, read the warnings given in paragraph on safety and in paragraph 1 of this chapter. The procedures described in this chapter concern only the main electrical circuits and should not be used to test electronic circuits of systems (such as anti-lock brake systems), and especially those used by electronic control units.
General information
1. A typical electrical circuit contains an electrical component, switches, relays, motors, fuses, fuse links, or circuit breakers associated with that component, and the wiring and connectors that connect the component to the battery and chassis. To help troubleshoot electrical circuits, wiring diagrams are provided at the end of this guide.
2. Before you begin troubleshooting an electrical circuit, study the relevant wiring diagram and gain a thorough understanding of the components in the circuit. Finding possible sources of failure is easier if you make sure that other components in the circuit are working properly. If several components or circuits fail at the same time, the fault may be related to their common fuse or ground connection.
3. Electrical circuit faults are usually caused by simple reasons such as: loose or corroded connection contacts, poor grounding, a blown fuse or fuse link, or a faulty relay (see paragraph 3 for a detailed description of how to test a relay). Before you begin testing circuit parts, inspect the condition of all fuses, wires, and connectors in the faulty circuit. Use wiring diagrams to determine which connections need to be tested to locate the fault.
4. The list of basic tools for troubleshooting electrical circuits includes a tester or voltmeter (for some tests, a 12-volt light bulb with test leads can also be used); battery powered indicator (also called break indicator); ohmmeter (for measuring resistance); battery with a set of control wires; a jumper wire, preferably with a fuse, that can be used to bypass the wires or electrical components being tested. Before you begin troubleshooting with instruments, determine the points to connect them to from the electrical diagram.
5. To find the source of an intermittent wiring fault (usually caused by a poor connection or damaged wiring insulation), you can simply move the wires. If the contact in the circuit appears and then disappears, then the source of the fault is in that place of the wiring. This method of testing can be used along with any others described in the following subparagraphs.
6. Besides bad contacts, there are two other main types of faults: open circuit and short circuit.
7. When a circuit is broken at any point, the component stops receiving current and, as a result, stops working, although the break in the circuit does not cause the fuse to fail.
8. Short circuits are usually caused by a breakdown in the insulation of electrical wiring, when wires or wires touch each other or the body of the wire. A short circuit usually blows the fuse of the corresponding circuit.
Detecting chain breaks
9. To locate an open circuit, connect one of the tester terminals or the negative terminal of the voltmeter to the negative terminal of the battery or to a good ground.
10. Connect the other terminal of the tester to the connector in the circuit being tested, preferably the one closest to the battery or fuse.
11. Turn on the circuit, then connect the tester terminal to the location closest to the area to be tested. Note that some circuits are only closed when the ignition switch is in a certain position.
12. The presence of voltage (as indicated by the light of the test lamp or the reading of the voltmeter) means that the circuit line between the corresponding connector and the battery is in good condition.
13. Continue checking the rest of the circuit in the same manner.
14. If a point where there is no voltage is found, then the section between this point and the previously checked point is faulty. Check it to find the fault. Most faults are caused by corrosion, breakage or loose contacts.
Short circuit detection
15. Before testing a 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 leads to its terminals.
17. Turn on the circuit, keeping in mind that some circuits are only closed when the ignition switch is in a certain position.
18. The presence of voltage (as indicated by the light of the control lamp or the reading of the voltmeter) confirms a short circuit.
19. If there is no voltage 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 terminal of the battery is connected to the "ground" - the engine-transmission-body assembly. Most electrical consumers have only the positive wire connected to them, and the negative conductor is the metal of the body. This means that the body ground is part of the circuit. Therefore, loose connections can result in a partial or complete break in the circuit. This can cause dim lights (especially if another circuit using the same ground point is on), slow motors (such as the windshield wiper motor or cooling fan motor), and interference from one circuit to another. Note that many vehicles use flexible ground straps to connect components to the body that do not have direct metal-to-metal contact with it, such as the engine-transmission assembly mounted on rubber mounts.
21. To check the reliability of the component ground, disconnect the battery and connect one lead of the ohmmeter to a point with a reliable ground. Connect the other lead of the ohmmeter to the point of the component being 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 the connection, clean both the contact point on the body and the wire tip (or the mounting surface of the unit housing) down to the metal. Remove all traces of dirt and corrosion, scrape off the paint with a knife to ensure a clean metal-to-metal connection. Reassemble the connection and tighten the fasteners carefully. If there are tips at the ends of the wires, install serrated washers between the tip and the housing to ensure a reliable connection. To prevent corrosion of the connection after restoration, lubricate it from the outside with technical petroleum jelly or silicone grease (or periodically spray special moisture-proofing agents on it).
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