Note. Before starting work, refer to the precautions given in paragraph «Safety first!» and in chapter 5A. The following checks are for testing main electrical circuits and should not be used to test sensitive electronic circuits (available, for example, in the anti-lock brake system), especially in cases where electronic control units are used (BEU) and multiplex network (see paragraph 1).
General information
1. A typical electrical circuit consists of an electrical element, switches, relays, motors, fuses, fuse links, or circuit breakers associated with that element, as well as wiring and electrical connectors that connect the element to the battery and ground on the chassis. To facilitate the exact determination of a fault in the circuit, electrical diagrams are given at the end of this chapter.
2. Before attempting to troubleshoot an electrical circuit, first study the relevant circuit diagram. You must have a complete understanding of the nature of the elements involved in a particular problem chain. The list of possible causes of a malfunction can be narrowed down by identifying the elements of this circuit that work correctly. If more than one element or circuit is failing at the same time, the problem is likely with a common fuse or ground.
3. Electrical faults are usually the result of simple causes such as poor contact or corroded connections/connectors, faulty ground, blown fuse or fuse, faulty relay (For detailed information on relay testing, see paragraph 3). Before checking items, visually inspect the condition of all fuses, wires, and connections in the problem circuit. Use the wiring diagrams to determine which connections need to be checked to pinpoint the exact cause of the problem.
4. The main instruments needed for troubleshooting electrical circuits include a tester or voltmeter: ohmmeter (for measuring resistance); battery and a set of test wires; changeover connecting wire (preferably with built-in circuit breaker or fuse), which can be used to bypass suspected wires or electrical items. Before attempting to solve a problem with test equipment, determine from the wiring diagram where the instrument should be connected.
5. Sometimes to search for intermittent faults in the wiring (usually due to poor or dirty contact in the connection / connector or damage to the insulation of the wires) it is useful to simply move or shake the wires and see if this causes a malfunction. This should narrow the problem area to a specific section of the wiring. Such a check can be used in conjunction with any of the checks described in the following parts of the paragraph.
6. In addition to faults caused by poor contact, two main types of faults can occur in the electrical circuit - open or short circuit.
7. As a rule, a break is caused by an open somewhere in the electrical circuit, which stops the supply of current to the consumer. The break prevents the element from operating, but does not cause the corresponding fuse to blow.
8. A short circuit is caused by a short somewhere in an electrical circuit, which allows the current flowing through the circuit to take an alternate path (usually by weight). A short circuit is usually caused by a breakdown in the insulation of the electrical wiring, which allows the power wire to touch either another wire or ground (for example, bodies). A short circuit will usually blow the corresponding fuse.
Note. On models equipped with a multiplex network (from model year 2001), to save energy and prevent battery drain, some functions of the electrical system can only be used for 30 minutes after the engine is turned off. Keep this in mind when troubleshooting the power supply circuits for these systems.
Functions affected
Windshield wipers. Power windows. Roof hatch. Interior lighting switched on by door contacts.
Audio equipment.
After this period, the BSI stops supplying power to these circuits. Start the engine to restore power. In addition, the BSI block may turn off some functions (heater fan, heated rear window) depending on the state of charge of the battery. If a malfunction is detected, make sure that the battery is properly charged.
Search for a break in the electrical circuit
9. To check the electrical circuit for an open, connect one tester or voltmeter lead to the negative battery terminal or to a known good ground point.
10. Connect the other wire to a connector on the circuit under test, preferably as close to the battery or fuse as possible.
11. Turn on the electrical circuit. Be aware that some circuits are only energized when the ignition switch is in a certain position.
12. If voltage is present (the indicator on the tester is on or the voltmeter shows voltage), this means that the section of the circuit between the corresponding connector and the switch is OK.
13. Continue to check the rest of the chain in the same way.
14. When achieved «dot», in which there is no voltage, this means that the cause of the malfunction must lie between this «dot» and the previous test «dot», in which the voltage was recorded. Most problems are caused by breakage, corrosion, or a loose connection.
Search for a short circuit in an electrical circuit
15. To test the electrical circuit for a short circuit, first disconnect the load from the circuit. A load or consumer is an element that uses an electric current. present in the circuit; such as lamp, electric motor, heating element, etc.
16. Remove the appropriate fuse from the circuit and connect a tester or voltmeter to the fuse socket terminals.
17. Turn on the circuit. Be aware that some circuits are only energized when the ignition switch is in a certain position.
18. If voltage is present (the indicator on the tester is on or the voltmeter shows voltage), it means that there is a short circuit.
19. If there is no voltage, but the fuse blows after the load is connected, this indicates an internal fault in the load.
Search for a short to ground
20. The negative terminal of the battery is connected to «weight», i.e. with metal parts of the power unit and the car body. Most systems are wired so that they receive only positive power. The current returns through the metal of the car body. This means that the fastening of the elements and the body are part of the electrical circuit. Therefore, loose or corroded supports can cause a range of electrical problems, from complete circuit failure to a puzzling partial failure. In particular, lights can burn dimly (especially when another circuit is running using the same mass point), electric motors can rotate slowly (e.g. wiper motors or radiator cooling fan motor). The operation of one circuit can have, on the one hand, an obvious, and on the other hand, incomprehensible influence on the other. Be aware that many vehicles have ground wires/busbars installed between certain components such as the powertrain and bodywork. They are usually installed in places where the metal surfaces of the elements do not come into contact with each other due to the presence of rubber supports, etc.
21. To test cell grounding, disconnect the battery and connect one ohmmeter lead to a known good ground point. Connect the other wire to the wire to be tested or to the ground connection to be tested. The ohmmeter should read zero. If this is not the case, check the connection as follows.
22. If the ground connection is suspected to be faulty, disassemble the connection and speckle the body contact surface and wire lug or mating element ground surface to a metallic sheen. Carefully remove all traces of dirt and corrosion and then scrape off the paint with a knife to ensure clean contact «metal to metal». When assembling, securely tighten all fastening elements of the connection. When reinstalling the wire lug, place a fine toothed washer between the lug and the body to obtain a clean and secure connection. When refinishing the joint, lubricate it with petroleum jelly or silicone grease to prevent future corrosion. Alternatively, apply (at regular intervals) an in-line ignition sealant or water-repellent lubricant.