Contents: Finding the source of a fault in an… ↧ Finding a break in the chain ↧ Finding a short circuit ↧ Checking the reliability of grounding ↧ Connectors ↧
The electrical circuits of a car include a consumer, switches, relays and wires connected according to the attached diagram (see below). Before you start troubleshooting, you should study the circuit and determine the possible source of the fault. For example, the task of troubleshooting is significantly simplified if you can check the serviceability of other consumers directly or indirectly connected to the suspected circuit.
If there is a failure of several consumers, then the most likely cause is a broken connection to ground or a blown fuse. As a rule, electrical equipment failures are caused by loose or corroded contacts, a blown fuse or a melted jumper. Troubleshooting is usually performed using a tester (voltmeter) or a test lamp, which are connected between the section of the faulty circuit and a well-cleaned ground.
By connecting a tester or a lamp in series along the circuit contour, you can identify a faulty section, which is detected by the loss of voltage or the lamp going out. To find a short circuit in the wires, you should remove the fuse of the circuit being tested and connect a lamp or voltmeter to the gap. A short circuit with ground is indicated by the lamp lighting up when the wires are swung from side to side (the tester should show voltage). When checking, keep in mind that some consumers receive power when the ignition key is in the Accessories or Run position. To check the reliability of the connection to ground, connect through an ohmmeter (or via a control lamp with a battery) the tested wire connection to the ground and a well-cleaned section of the ground. If the ohmmeter shows a circuit (or the lamp will light up), then the ground connection is reliable. Otherwise, the ground contact is broken. Keep in mind that in most cases, the ground serves as a return current conductor connecting the circuit to the negative pole of the battery. Therefore, a broken ground connection, or a break in the return current circuit to the battery, can be the main cause of failure.
Finding the source of a fault in an electrical system - general description
A typical electrical circuit consists of an electrical component, switches, relays, motors, fuses, fuse links or circuit breakers, and the wires and connections that connect all the components together and to the battery and the vehicle ground. To make troubleshooting easier, electrical diagrams of the vehicle's electrical system are provided at the end of this Chapter.
Before you begin testing a faulty circuit, first study the circuit diagram to understand what elements it consists of. You can find the source of the fault faster if you determine which elements of the circuit are working properly. If several elements or circuits fail at once, the problem is likely a blown fuse or poor grounding, since one fuse is often responsible for several circuits.
Problems with the electrical system are usually caused by simple causes, such as oxidized or unreliable contacts, a blown fuse, a burnt-out jumper, or a faulty relay. Visually check the condition of all fuses, wires, and connections in the faulty circuit before checking other elements of the circuit. If you are going to use instrumentation, use the circuit diagrams to determine which connections need to be checked to detect a fault.
The main devices required to find faults in an electrical circuit are:
- a) Circuit testing device or voltmeter (or a 12 volt light bulb with connecting wires).
- b) Control lamp with power supply (or a device for checking the integrity of circuits).
- c) Ohmmeter (for measuring resistance).
- d) Battery.
- d) Probes with wires.
- e) A jumper cable, preferably with a circuit breaker or fuse, that can be used to test wires or electrical components.
Before you begin troubleshooting using test equipment, study the circuit diagrams to determine the connection points.
To find a loose connection or short circuit point (usually due to a poor or dirty connection, or damaged insulation) the wires can be shaken by hand to see if the circuit breaks when the wire moves. In this way, a point with a poor connection or a point where a short circuit occurs can be found. This method of testing can be used along with the other tests described in the following subsections.
Besides problems associated with a poor connection, an electrical circuit can have two other main faults - an open circuit or a short circuit.
An open circuit can be caused by a broken wire or a loose connection somewhere in the circuit that prevents current from flowing. An open circuit will cause a piece of electrical equipment to fail to operate, but will not cause the fuse for that circuit to blow.
Short circuit faults are caused by a short somewhere in the circuit, causing the current flowing in the circuit to flow through another circuit, most often to ground. A short circuit is usually caused by a break in the insulation, allowing the supply wire to touch either another wire or a grounded element, such as the body. The short causes the fuse for the corresponding circuit to blow.
Before troubleshooting or repairing an electrical system, remember that different types of wires have different colors.
Finding a break in the chain
To find an open circuit, connect one of the test light probes to the negative battery terminal or vehicle ground.
Connect the second probe to a connection in the circuit being tested, preferably located as close to the battery or fuse as possible.
Apply voltage to the circuit. Remember that some circuits only have voltage when the ignition key is turned to a certain position.
If voltage is present (what will the illuminated control lamp or voltmeter readings indicate?), this means that the part of the circuit between the connection and the battery is good.
Continue checking the rest of the chain in the same manner.
When you find a point where there is no voltage, it means that the source of the problem is between that point and the last point where voltage was present. Most problems are caused by a bad connection.
Finding a short circuit
To test a circuit for a short circuit, first disconnect the circuit's load (loads are the electrical components that consume electricity, such as light bulbs, motors, heating elements, etc.).
Remove the fuse for the appropriate circuit and connect a test light or voltmeter to the fuse connection terminals.
Apply voltage to the circuit. Remember that some circuits only have voltage when the ignition key is turned to a certain position.
If voltage is present (what will the illuminated control lamp or voltmeter readings indicate?), this means that there is a short circuit in the circuit.
If there is no voltage, but the fuse still blows when connecting the load elements, then one of these elements is faulty.
Checking the reliability of grounding
The negative terminal of the battery is connected to the vehicle's "ground" - the metal of the engine/gearbox and the car body - and most electrical systems are designed so that only one supply wire goes to the electrical component, with the current returning through the metal of the car body. This means that the electrical component's mount and the car body are part of the electrical circuit. Therefore, a poor or corroded mount can cause a wide range of problems in the electrical system, from complete failure of the circuit to unreliable operation. In particular, light bulbs may glow dimly (especially if another circuit is connected that uses the same ground), engines (for example, windshield wiper motors or radiator cooling fan) may operate slowly and turning on one circuit may affect the operation of another circuit. Note that many vehicles use grounding straps between various components of the vehicle, such as between the engine/gearbox and the body, usually where there is no metal to metal contact between the components due to the use of rubber mounts etc.
To check for proper grounding, disconnect the battery and connect one of the ohmmeter probes to the vehicle's ground. Connect the other probe to the wire or ground point you want to check. The resistance registered by the ohmmeter should be zero; if not, check the connection as follows.
If you think the connection is not OK, disassemble the connection and clean the contact surface and the wire terminal or the surface of the grounded element to bare metal. Remove all dirt and corrosion, then use a knife to remove the paint layer to get a reliable metal-to-metal connection. When reassembling, securely fix the connection; when installing the wire terminal, use toothed washers between the terminal and the body. After connecting, apply a layer of Vaseline or silicone grease to the connection to prevent corrosion.
Connectors
The vehicles in question use multi-pin connectors with plastic housings. The mating parts of the connectors are held in place by latches or a central screw (for example in the connectors under the dashboard). The latches are released with a thin, flat tool. Some connectors may have more than two latches. To check the circuit without disconnecting the connector, the probes of the device are inserted from the back of the connector until they stop in the terminal.