Note. Before you begin, refer to the prejudices in the section "Safety first!" (at the beginning of this guide). The following checks are for general circuit tests and should not be applied to sensitive electronic circuits (such as ABS), in particular where electronic control units are used.
General information
1. A conventional electrical circuit consists of electrical components - switches. relays, motors, fuses, fuses, etc., connected by wires to the positive and negative terminals of the battery, as a power source. To facilitate troubleshooting in electrical circuits, electrical circuit diagrams are provided at the end of this chapter.
2. Before starting troubleshooting, carefully study the corresponding circuit according to the diagram in order to get a complete understanding of its components. A possible source of failure can be determined by verifying that other circuit components are functioning normally. If several components or circuits fail at the same time, the fault is most likely in the appropriate fuse or ground/negative wire connection.
3. Electrical problems usually occur for simple reasons such as corroded contacts, poor ground connections due to oxidation, a blown fuse or fuse, a faulty relay (refer to paragraph 3 for relay test information). Therefore, before starting a detailed check of the components of the problem circuit, visually check the condition of all its fuses, wires and connections. Follow the diagram to see which pins and connections should be checked to determine the problem.
4. For most checks, you only need to have the following basic tools; tester or voltmeter (for some checks, a 12-volt test light with two wires is also suitable); probe (self-powered control lamp), ohmmeter (for measuring resistance), battery and a set of wires; wires - "cigarette lighters" with a circuit breaker or built-in fuse that can be used to bypass suspicious circuit elements. Before trying to troubleshoot using tools, study the diagram to find out which points it is advisable to connect the device to.
5. To find "wandering" circuit failure, which is usually due to poor contact or insulation, move the wiring to see if the malfunction does not disappear or appear. This troubleshooting method can be combined with the methods described below.
6. In addition to problems associated with poor contacts, two main types of faults can appear in the electrical circuit - open and short circuits.
7. An open circuit interrupts the electrical current, stopping the operation of the system components, but does not cause a fuse to blow.
8. Short circuit (KZ) allows electric current to leave the circuit "bypass" by, in most cases on the body. Usually a short circuit occurs due to aged or damaged wire insulation, which makes it possible "naked" wire to close to another wire, or case. Usually, during a short circuit, a fuse in the corresponding circuit is lit.
9. Fuses are designed to protect circuits from overload. A blown fuse indicates a problem in the protected circuit - before replacing the fuse, find the cause of the blown fuse and eliminate it. Replace the blown fuse with a new one of the prescribed rating. Installation "bugs" and fuses rated for high current will cause the circuit to overheat or cause a fire.
Finding an open circuit
10. To detect an open circuit, connect one tester lead or negative lead of a voltmeter to the negative battery terminal, or a good ground (bodywork). Connect the other terminal of the instrument to a connector on the circuit under test, preferably one closest to the positive battery terminal or fuse. Apply power to the circuit. Note that some circuits only receive power when the ignition key is turned to a certain position. Presence of voltage (as evidenced by the glow of the control light or the deviation of the instrument arrow) means that the section of the circuit between the connection point and the positive terminal of the battery is good. Continue checking the circuit in the same way. If the point at which there is no voltage is found, then the section of the circuit between this point and the previous one, where the voltage was present, is faulty. Check it to determine the problem. Most failures are due to bad contacts - breakage, corrosion or weakening.
Short circuit search
11. Before checking the circuit for short circuit, disconnect the load from this circuit (components - current consumers - lamps, motors, heating elements, etc.).
12. Turn off the ignition. To de-energize the circuit, remove the appropriate circuit fuse and connect the wires of a tester, voltmeter, or test light to its contacts.
13. Apply power to the circuit, bearing in mind that some circuits only receive power when the ignition key is in a certain position. Presence of voltage (the control lamp lights up or the instrument pointer deviates) confirms the presence of a short circuit in the circuit. If there is no voltage at the same time, and the fuse still blows when the load is connected, then the fault is in the load itself.
Break detection "masses"
14. The negative terminal of the battery has electrical contact with "weight" - engine block, gearbox, car body. Only the positive wire is suitable for most current consumers, the negative conductor is the body. This means that the mass is a section of the chain. Thus, loose connections can lead to an open circuit - partial or complete. This can cause the lights to dim (especially if another consumer is switched on using the same ground connection point), deceleration of motor rotation (wiper motor or heater fan motor) and the influence of one circuit on the operation of another. Many vehicles use flexible braided copper tapes (tires) connections of masses that are not directly electrically connected to each other, for example, as an engine / gearbox block to the body, which is installed on the body on rubber insulating pads of supports.
15. In order to check the reliability of contact with the mass of a particular component, disconnect the battery, then connect one wire of an ohmmeter to the body, and the second wire to the tested point of the component. The ohmmeter should read zero, otherwise check the component ground connection as follows.
16. If there is a suspicion that the connection to ground is broken, disassemble this connection, clean the contact point on the body and the wire tip (or the mating surface of the component body) to metal. Remove all traces of dirt and corrosion, and scrape off the paint with a knife so that the metal-to-metal joint is clean. Assemble the connection and tighten the fasteners. If there are looped lugs on the ends of the wires, install notched washers between them and the housing. To prevent corrosion of the joint, lubricate the outside of the joint with petroleum jelly or silicone grease (do it regularly).
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