1. Always keep in mind the basic features of automotive circuits
The basic features of automotive circuits are low voltage, single line, parallel and negative hitch. When there are more automobile circuits to be expressed in an automobile wiring diagram, the reader will feel that the circuits are complicated. If the basic characteristics of automotive circuits are kept in mind during the reading, it will not be difficult to read the more complicated automotive circuits. According to the basic characteristics of automotive circuits, in reading and fault query should be clear on the following points:
① Automotive electrical system using a single wire connection
Automotive power supply, generator armature terminal and battery positive stake with a wire connected, usually with a positive battery stake connection line or starter motor solenoid switch on the power line terminal as the power supply of automotive circuits at the positive end. Each electric device in the automotive circuit is connected to the positive terminal of the power supply with only one wire, if the power connection terminal of an electric device is also connected to other electric devices, it means that other electric devices and the electric device **** power line. All electrical equipment and power supply positive connection is a single wire.
② The electrical equipment are connected in parallel
Electrical equipment and power supply may be connected in series with fuses, switches or relays and other devices, but no matter how many electrical equipment with the electrical equipment connected to the relationship between the electrical equipment is still in parallel with the relationship between the electrical equipment. If two or more electrical devices are connected to the positive terminal of the power supply through a fuse, it means that these two or more electrical devices use the same protective element. If the two power equipment through a relay contact or switch contact, and then connected to the positive end of the power supply, it shows that the two power equipment circuit is controlled by the same relay or switch.
③ The negative end of the hitch is the negative pole of the power supply
Automotive circuits in the electrical equipment is usually only the positive connection line, through the shell connected to the engine body, body or frame and other metal connections to the negative pole of the power supply (the negative pole of the battery and generator), that is, through the hitch to connect the negative pole of the power supply. While some electrical and electronic devices have wires connecting the positive and negative terminals of the power supply, these appliances or electronic devices do not have a hitch in the shell itself, but through the wire hitch. If these appliances or electronic devices are connected to the negative terminal connecting wire are connected to a certain wire, then this wire is these appliances or electronic devices of the public **** lap wire.
2. Fully understand the automotive wiring diagrams and regulations
To fully understand the characteristics of a variety of automotive wiring diagrams and different countries, different automotive companies, automotive wiring diagrams of different methods.
①Make full use of the characteristics of different automotive circuit diagrams
The schematic diagrams, wiring diagrams and various wiring harness diagrams of automotive circuits have their own strengths and weaknesses. Some automotive information will provide two or more kinds of automotive circuit diagrams at the same time, to take full advantage of the characteristics of the various circuit diagrams, their advantages complement each other, in order to improve the ability to read the diagrams, to facilitate the search for automotive circuit failures.
② Familiarize yourself with the different representations of automotive circuits
The symbols of automotive wiring diagrams have relevant national standards, but different countries and different automotive companies are accustomed to drawing automotive wiring diagrams according to their own style. Before reading these automotive circuit diagrams, you must be very clear about the characteristics of the circuit diagrams, the representation of the devices, wires and terminals labeled meaning, so as to avoid difficulties in reading the diagrams.
3. Familiar with the structure and working principle of the electrical and basic circuits
① Familiar with the structure of the automotive electrical late Wang and electronic devices
Automotive circuits in the electrical and electronic control device components are composed of the basic elements of automotive circuits, familiar with the structure of the electrical and electronic control devices and the basic principle is to analyze the circuit principle of the electrical system to understand the connection relationship, to carry out circuit troubleshooting. Familiarize yourself with the structure and basic principles of the electrical and electronic control devices is to analyze the circuit principle of the electrical system, understand the connection of the line, the basis of circuit diagnosis.
② Familiar with the basic circuits and types of automotive systems
Automotive circuits in some electrical systems have several basic forms of circuit structure. For example, the starter circuit has a starter switch direct control, with a starter relay, with a starter protection function and other structural forms. Fully understand the basic composition of these circuits, the principle of operation and characteristics, in reading the circuit of various models will not be difficult.
4. Familiarize yourself with the function and state of various switches and relays
Automotive circuit diagrams, familiar with the function of the state of switches and relays is also very important.
① Fully understand the function of the switch or relay
Some composite switches have more than one gear and more than one connecting terminal, when reading the map, first of all, we must fully understand the role of the switch gears and their connected circuits; we must be familiar with the relay contacts connected to the controlled circuit and the relay coil is connected to the control circuit, so that we can fully understand the function of the relay.
② Familiar with the switch and relay circuit in different states
In the automotive circuit principle and fault analysis, you need to fully understand the switch or relay circuit path in different states. In the automotive circuit diagram, switches and relays are represented in the initial state, in addition to the initial state of the switch or relay to open and close the situation and the controlled circuit of the on-off situation, but also to be very clear about the operation of the switch, relay coils are energized, and the change of its contacts open and close the situation and the controlled circuit of the on-off situation.
5. Distinguish the relationship between the interrelated circuits
In automotive circuits, a system circuit may have multiple devices and multiple branch circuits, there is a certain relationship between the various devices and circuits, when a circuit failure, it will affect the other circuits work. Understand the relationship between these circuits, to understand the principles of automotive circuits and circuit failure analysis are of great help.
① Parallel relationship
For example, the turn signal circuit on the same side of the front and rear turn signal light circuits is a parallel relationship, they are controlled by the same flasher, when one of the turn signal or its circuit breakage or short-circuit faults, it will be due to the equivalent resistance of the circuit changes to make the flash frequency change. Clear turn signal circuit of this parallel relationship, when there is a single turn signal flash frequency abnormality, it will be associated with the side of the turn signal circuit failure.
② control and be controlled
Relay coil circuit and relay contacts connected to the circuit between the control and be controlled. Clearly this point, in the analysis of the contacts connected to the circuit can not work properly, in addition to thinking of the circuit, the circuit appliances and the possibility of failure of the relay contacts themselves, it will certainly not forget that the relay coil circuit (including line relay coils and control switches, etc.) is also one of the causes of failure.
③ control target correlation
Automotive electronic control system sensor circuits and actuator circuits are connected to electronic controllers, one is to achieve a certain control goal and provide the controlled object state parameters of the information source circuit, the other is the implementation of the control goal of the control execution circuit, associated through the controller. Abnormalities in the sensor circuits have a direct effect on the operation of the control actuator circuits. Therefore, a control actuator does not work or work abnormally, in addition to the cause of the actuator itself, the cause of the failure should also include all the relevant sensors and circuits.
6. Proficiency in circuit analysis
An automotive circuit with a certain function consists of the positive terminal of the power supply through the protective device (fuse or fusible link), the control device (switch or relay contacts), the electrical equipment and the corresponding wiring. Therefore, the method of circuit analysis can help us analyze the principle of the circuit and the cause of circuit failure.
① skilled use of circuit analysis in the map
In the automotive circuit diagram to analyze the circuit principle, available circuit analysis to analyze the circuit access, generally using sequential analysis, that is, from the positive pole of the power supply through the fuse (some circuits may not have), switches (or relay contacts), the lap of the electrical equipment, and then back to the negative pole of the power supply. When more circuits are represented on the circuit diagram, the reverse method can also be used, i.e., from the negative power connection terminal of the power-using equipment, through the switch (or relay contacts), the fuse (if any) to the positive connection terminal of the power supply.
② Application of circuit analysis in automotive circuit fault analysis and diagnosis
Familiar with the circuit analysis method is not only useful for understanding the principle of the circuit, it is also important for circuit fault analysis and fault query. For example, an electrical device does not work, the circuit analysis method to determine whether the circuit is a circuit breaker or short circuit fault; in determining the automotive circuit for the circuit breaker, the automotive circuit can be in the circuit from the positive end of the power supply close to the beginning of the end, by checking the voltage of each connection point by point to find the break; in determining the automotive circuit for the short-circuit fault, can be in the automotive circuit circuit from the power supply to the furthest end of the positive end of the circuit, the power supply to disconnect each connection point by point by point to start. After determining the short circuit fault, you can start from the furthest end of the positive pole of the power supply in the circuit of the car, and then disconnect each connection point by point (voltage detection method) to find the short circuit place.