Attention! The procedures described below provide a general diagnosis of the condition of the main electrical circuits, but should not be used to test easily vulnerable electrical systems (such as ABS), especially those that include electronic control modules (ECM).
General information
A typical electrical circuit consists of an electrical consumer (working component), a set of switches, relays, actuator motors, fuses, fuses / circuit breakers related to the operation of this component, as well as connecting wiring, its contact terminals and connectors. For the purpose of simplification of performance of diagnostic procedures in the last Section of the present Chapter schemes of electric connections of various systems of electric equipment of the car are given.
Before starting to search for the reasons for the failure of a failed consumer of electricity, carefully study the corresponding electrical circuit, try to imagine as clearly as possible the principle of operation of the components that make up the suspect circuit. The list of possible causes of failure can be minimized by excluding properly functioning components from the list that are relevant to the operation of the circuit under test. If several components fail at the same time, the most likely cause of the failure is the failure of a fuse / fuse common to the corresponding circuits, or a ground fault.
Most often, electrical equipment failures are explained by the simplest causes, such as corrosion damage or loosening of terminal connections, failure of a fuse or fuse, relay failure, etc. Before starting to search for internal defects of the failed component itself, carefully check the condition of all fuses, connectors and connecting wires related to its operation.
To determine the list of units and terminal connections to be checked, study the corresponding wiring diagrams.
Diagnostic equipment needed when troubleshooting electrical equipment should include a universal circuit meter / voltmeter (a 12-volt lamp with a set of connecting wires will also work for some tests), probe lamp with individual power supply (sometimes also called a conductivity meter), an ohmmeter, a power supply with a set of connecting wires, as well as a set of jumper wires equipped with various types of connecting terminals and, preferably, a built-in circuit breaker or fuse (for shunting suspicious sections of a circuit or electrical components). Before resorting to the use of diagnostic equipment, carefully study the wiring diagram of the components of the corresponding circuit (see Section Single lock with ETACS, Galant models 1990-1993 issue).
To find the cause of an intermittent failure (violations of this kind are usually associated with the oxidation of the contact terminals, or loosening of the fastening of the terminal connections of the electrical wiring) a simple circuit check can be performed by twitching various sections of the wiring of the corresponding circuit, as a result of which a defective section of the circuit is localized. This check can be performed in conjunction with any of the following in the relevant subsections.
In addition to problems associated with a violation of the quality of electrical connections, open circuits and short circuits in the circuit should be attributed to the most probable and frequently occurring failures of electrical circuits.
An open circuit is usually caused by mechanical damage to the conductive wires or disconnection of the contact terminals, which leads to the opening of the electrical circuit and the cessation of the circulation of electric current in it. An open circuit will stop the working component from functioning, but the related fuses/fuse links will not fail.
A short circuit is a short circuit of its electrical wiring that is not provided for by the design of the circuit. In this case, the current begins to circulate along the shortest path, usually going to ground. Short circuits most often turn out to be associated with a violation of the integrity of the insulation of the electrical wiring and without fail lead to the failure of the corresponding fuses / fuses.
Checking the presence of voltage in the circuit
Checking the presence of voltage is one of the standard checks in the event of a failure of any consumer of electricity. Connect one of the leads from a circuit meter or voltmeter to the negative battery terminal, or any of the positively grounded points on the vehicle's chassis/engine. Connect the second wire of the instrument to the terminal connection of the circuit under test, preferably closest to the battery or fuse. Apply power to the circuit. Be aware that some circuits are only energized in certain positions of the ignition switch. If tension is present (the meter lamp turns on, or the corresponding reading is fixed on the voltmeter indicator), then the segment of the circuit between the terminal connection being checked and the battery is working.
Continue the test in the same vein, alternately moving from one terminal connection of the circuit to another, moving in the direction from the battery / fuse. The faulty section of the circuit will be located between the point at which the device does not register the presence of voltage and the previous tested and working terminal connection. Most often, the cause of the failure is a broken electrical wiring, or oxidation / loosening of the terminal connection.
Search for the causes of a short circuit
Disconnect the consumer first (And) electric power of the tested circuit (consumers of electricity, or the payload of the circuit, are the components for the operation of which the current circulating in the circuit is consumed, such as lamps, electric motors, heating elements, etc.). Remove the fuse that protects the circuit under test and connect a test lamp or voltmeter to its installation terminals. Apply power to the circuit. Remember that some of the circuits are only energized in certain positions of the ignition switch. If voltage is present at the fuse terminals, then a short circuit has occurred in the circuit (pull the wiring, as a short circuit can be caused by rubbing its insulation and be unstable). If there is no voltage, but the fuse after replacement continues to blow when power is applied to the circuit, then there is an internal defect of the consumer (to her) electricity, switch or electrical wiring insulation.
Search for ground faults
The negative battery terminal is grounded at "mass", which is the metal of the power unit, chassis and car body elements. The electrical circuits of most electrical equipment are constructed in such a way that the electrical wiring is used only to supply power to the consumer from the positive terminal of the battery, while the current is returned to the battery through the mass metal. The foregoing means that the fasteners of electricity consumers form the return part of the electrical circuit. In view of the situation described, loosening or corrosion of the supporting elements of the working component of the circuit entails a malfunction of the circuit (from complete failure of the last failure to partial failure of various sections of the circuit). In particular, as a result of loosening fasteners, the brightness of lighting fixtures may decrease (especially if there is a common ground with another circuit), or the speed of rotation of the electric motor (e.g. wiper drive or cooling fan). In this case, the failure of one circuit can cause a disruption in the functioning of another, externally in no way connected with the failed one. Please note that on many vehicles certain nodes are connected to each other by special grounding buses. Such tires are used in cases where there is no direct contact between the metal parts of the blocks due to the equipment of the supports with flexible rubber bushings (as, for example, in the supports for attaching the power unit to the chassis of the car).
To test for proper component grounding, disconnect the battery and connect one of the ohmmeter leads to a known good ground point on the vehicle. Connect the second test lead to the ground point of the component under test. The device should fix zero resistance, otherwise you should check the connection (see below).
If you suspect a violation of the quality of the terminal connection, disassemble the ground contact assembly and clean the mating surfaces of the terminals to bare metal. Try to completely remove all traces of corrosion and dirt, then scrape off the paint with a knife, achieving unambiguous metal-to-metal contact. When assembling the assembly, take care of the fastener tightening strength. Between the wiring terminals and the ground contacts, to ensure the quality of the electrical connection, lay knurled washers. Coat mated terminal connections with acid-free Vaseline or silicone grease to prevent future corrosion. Ignition sealant spray and water-repellent lubricant are also good tools.
Finding open circuits
Unstable failures of electricity consumers most often turn out to be associated with a violation of the quality of terminal connections due to oxidation or loosening of fasteners. Often, simply tugging on the associated wiring harness/electrical connector is enough to bring a component to working order. The easiest way to find an open circuit is to check its working areas for conductivity. Turn off the power supply to the circuit and use the meter equipped with an independent power supply. Connect the meter leads to both outputs of the circuit under test (power supply terminal and a well-grounded point). If the device detects the presence of conductivity (zero resistance/probe lamp operation), therefore, the tested section of the circuit is working. Otherwise, a break occurs. In a similar way, the correct functioning of the switches can be checked.