If there is a failure of several consumers, then the most likely cause is a broken ground connection or a blown fuse. As a rule, failures of electrical equipment are caused by weakening of contacts or their corrosion, blown fuse or jumper melting. Troubleshooting is usually done with a tester (voltmeter) or a test lamp, which are connected between the section of the faulty circuit and a well-stripped ground.
By connecting a tester or a lamp in series along the circuit loop, you can identify a faulty section, which is detected by a power failure or lamp extinction. To search for a short circuit in the wires, you should get the fuse of the circuit under test and connect a lamp or a voltmeter to the gap. A short circuit with ground is indicated by the lamp lighting up when the wires are wiggled from side to side (the tester should show the 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 through a test lamp with a battery) a checked wire-to-ground connection and a well-cleaned ground area. If the ohmmeter shows a circuit (or the lamp will turn on), then the ground connection is reliable. Otherwise, ground contact is broken. Keep in mind that in most cases, the ground serves as a return conductor connecting the circuit to the negative pole of the battery. Therefore, a broken ground connection, or an open circuit in the return current to the battery, can be the main cause of failure.
Finding the source of a malfunction in an electrical system - a general description
A typical electrical circuit consists of a piece of electrical equipment, switches, relays, motors, fuses, blown jumpers or circuit breakers, and wires and connections that connect all the elements together and connect them to the battery and «mass» car. In order to simplify the process of troubleshooting, at the end of this Chapter are electrical diagrams of the vehicle's electrical system.
Before starting to check a faulty circuit, first study the circuit diagram of this circuit in order to understand what elements it consists of. The source of the malfunction can be found faster if you determine which of the elements of this circuit are working properly. If several elements or circuits fail at once, the problem is probably a blown fuse or poor grounding, since often one fuse is responsible for several circuits.
Problems with the operation of an electrical system are usually caused by simple causes such as oxidized or unreliable contacts, a blown fuse, a blown blown jumper, or a faulty relay. Visually check the condition of all fuses, wires, and connections on the faulty circuit before checking other items» chains. If you're going to be using test equipment, use the circuit diagrams to determine which connections you need to check to find a problem.
The main instruments needed to find a fault in the electrical circuit are:
- A) Circuit Tester or Voltmeter (or a 12 volt light bulb with connecting wires).
- b) Control lamp with power supply (or a continuity tester).
- V) Ohmmeter (for measuring resistance).
- G) Battery.
- d) Probes with wires.
- e) Loop wire, preferably with a circuit breaker or fuse, which can be used to test wires or electrical equipment.
Before troubleshooting using test equipment, study circuit diagrams to determine connection points.
To find a loose connection or short circuit point (usually due to a bad or dirty connection, or damaged insulation) the wires can be shaken by hand to see if the circuit breaks when the wire is moved. In this way, you can find a point with an unreliable connection or a point where a short circuit occurs. This test method can be used along with the rest of the tests described in the following subsections.
In addition to the problems associated with a bad connection, the electrical circuit can have two other main faults - the presence of an open circuit or a short circuit.
An open in the circuit can be caused by a break in some wire, or by a lack of connection somewhere in the circuit, preventing current from flowing. An open in the circuit will cause the failure of any piece of electrical equipment in operation, but will not blow the fuse of this circuit.
Short circuit faults are caused by a short somewhere in the circuit, which causes the current flowing in the circuit to start flowing in another circuit, and most often «mass». A short circuit is usually caused by a broken insulation that allows the power wire to touch either another wire or a grounded item such as a body. A short circuit will blow the fuse of the corresponding circuit.
Before locating the source of a fault or when making repairs to an electrical system, remember that different types of wires have different colors.
Finding the break in the chain
To find an open circuit, connect one of the test light probes to the negative terminal of the battery or «mass» car.
Connect the second probe to a connection in the circuit under test, preferably as close as possible to the battery or fuse.
Apply voltage to the circuit. Do not forget that in some circuits there is voltage only if you turn the key in the ignition switch to a certain position.
If voltage is present (what will be indicated by a lit control light or voltmeter readings), 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 way.
When you find the point where there is no voltage, it means that the source of the fault lies 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 the circuit for a short circuit, first disconnect the circuit load (loads are items of electrical equipment 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 terminals.
Apply voltage to the circuit. Do not forget that in some circuits there is voltage only if you turn the key in the ignition switch to a certain position.
If voltage is present (what will be indicated by a lit control light or voltmeter readings), this means that there is a short circuit in the circuit.
If there is no voltage, but the fuse still blows when the load elements are connected, then one of these elements is faulty.
Checking the reliability of grounding
The negative battery terminal is connected to «mass» vehicle - the metal of the engine/gearbox and the vehicle body - and most electrical systems are designed so that only one supply wire is connected to the electrical component and the current is returned through the metal of the vehicle body. This means that the fastening of the electrical equipment element and the car body are part of the electrical circuit. Therefore, a poor or oxidized fastening can cause a large number of malfunctions in the electrical equipment system, from complete failure of the circuit to unreliable operation. In particular, light bulbs can burn dimly (especially if another circuit is switched on using the same ground), engines (e.g. 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 bonding ground strips between various parts of the vehicle, such as between the engine/transmission and the body, usually when there is no metallic contact between the components due to the use of rubber mounts, etc.
To check the grounding, disconnect the battery and connect one of the ohmmeter probes to «mass» car. Connect the second probe to the wire or ground point you want to test. The resistance recorded by the ohmmeter must be zero; if not, check the connection as follows.
If you think the connection is not good, disassemble the connection and clean to bare metal the contact surface and the wire terminal or the surface of the grounding element. Remove all dirt and corrosion, then use a knife to remove a layer of paint in order to obtain a reliable metal-to-metal bond. When assembling, fix the connection securely; 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
On the vehicles in question, multi-pin connectors with plastic housings are used. Mating connectors are held in place by latches or a central screw (e.g. in the sockets under the instrument panel). The latches are disengaged 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 at the terminal.