Contents: Checking for voltage ⬇ Short circuit detection ⬇ Checking the grounding serviceability ⬇ Conductivity checks ⬇ Localization of the break ⬇
Repair procedures and diagnostic codes for electronic control systems are discussed in Chapter 5.
A typical electrical circuit may include: an electrical component, various switches, relays, motors, fuses, circuit breakers, or circuit breakers associated with the component, and the wiring and electrical connectors that connect the component to the battery and body ground. To make it easier to troubleshoot electrical circuits, schematic diagrams of electrical connections are included at the end of the Manual.
Before you start troubleshooting any of the electrical circuits, carefully read the corresponding diagram in order to have as clear an idea of its functional purpose as possible. Narrowing the troubleshooting area is usually accomplished by gradually identifying and eliminating normally functioning components of the same circuit. When several components or circuits fail at the same time, the most likely cause of failure is the burnout of the corresponding fuse or a ground fault (different circuits in many cases can be shorted to one fuse or ground terminal).
Electrical equipment failures are often due to simple causes such as corrosion of terminals or failure of a fuse or relay. Perform a visual inspection of the condition of all fuses, wiring, and electrical connectors in the circuit before proceeding to more specific inspections of the circuit components.
When using diagnostic equipment to troubleshoot a fault, carefully plan in accordance with the electrical diagrams included at the end of the Manual where and in what sequence the equipment should be connected in order to most effectively identify the fault.
Basic diagnostic tools include an electrical circuit tester or voltmeter (a 12-volt test light with a set of connecting wires can also be used) and a tester, which includes a light bulb, its own power source and a set of connecting wires. In addition, a jump start cable kit equipped with alligator clips and preferably a circuit breaker should always be carried in the vehicle, which can be used to bypass and connect various electrical components during circuit diagnostics. As mentioned above, before you start checking the circuit using diagnostic equipment, determine the connection points using the diagrams.
Checking for voltage
Checks for the presence of voltage are performed in the event of a malfunction of the circuit. Connect one of the electrical circuit tester leads to either the negative battery terminal or a well-grounded point on the vehicle body. Connect the other tester lead to the terminal of the circuit's electrical connector, preferably the one closest to the battery or fuse. If the tester's indicator light comes on, there is voltage on that section of the circuit, which confirms that the circuit between that terminal and the battery is working properly. Continuing in a similar manner, explore the rest of the outline. The detection of a lack of voltage indicates the presence of a fault between this point of the circuit and the last of the previously checked points (where the voltage was present). In most cases, the cause of failure is loose electrical connections and poor contact quality.
Note: Remember that power is supplied to some of the on-board electrical circuits only in certain ignition switch positions.
Short circuit detection
One method of finding a short circuit is to remove the fuse and connect a test lamp or voltmeter in its place. There should be no voltage in the circuit. Pull the wiring while watching the test lamp. If the lamp starts to blink, there is a short to ground somewhere in the harness, possibly caused by a wire insulation failure. A similar check can be performed for each of the circuit components, including switches.
Checking the grounding serviceability
This test is performed to determine the reliability of the component grounding. Disconnect the battery and connect one of the wires of the self-powered test lamp to a known good ground point. Connect the other wire of the lamp to the harness or terminal being tested. If the lamp lights up, the grounding is OK (and vice versa).
Conductivity checks
The test is carried out to identify breaks in the electrical circuit. After disconnecting the power supply to the circuit, check it using a test lamp equipped with an independent battery. Connect the test leads to both ends of the circuit (or to the "power" end (+) and a well-grounded point on the body), if the test lamp lights, there is no open circuit in the circuit. Failure of the lamp to turn on indicates a violation of the circuit conductivity. In a similar way, you can check the serviceability of the switch by connecting a tester to its terminals. When the switch is turned to the "On" position, the test indicator lamp should light.
Localization of the break
When diagnosing a suspected circuit break, it is quite difficult to visually detect the cause of the malfunction, since inspecting the terminals for corrosion or damage to the quality of their contacts is difficult due to limited access to them (usually the terminals are covered by the connector housing). A sharp jerk of the connector housing on the sensor or its wire harness in many cases leads to the restoration of conductivity. Keep this in mind when trying to isolate the cause of a suspected open-loop circuit failure. Intermittent failures may be caused by oxidation of terminals or poor quality contacts.
Diagnosing electrical circuit faults is not a difficult task at all, provided that there is a clear understanding that current is flowing to all electrical loads (lamp, electric motor, etc.) from the battery through wires via switches, relays, fuses, fusible links, and then returns to the battery through the vehicle ground. Any problems associated with the failure of electrical equipment can only be caused by the interruption of the supply of voltage to this electrical equipment.
Text taken from this website (Skodabook.ru)