Characteristics and reading essentials of automobile circuit diagram

Taking Santana 2000GSi as an example, this paper introduces the reading essentials of Volkswagen circuit diagram. The following figure is the circuit diagram of the electronically controlled gasoline injection ignition system of Santana 2000GSi automobile engine provided by the automobile manufacturer, which is close to the electrical schematic diagram. Circuit diagram of electronically controlled gasoline injection and ignition system for Santana 2000GSi automobile engine; B- air conditioning compressor signal; C- self-diagnosis electronic circuit; D- engine speed signal; E- vehicle speed signal; F60—- idle switch; G6- fuel pump; G28—- speed sensor (gray plug); G39—- oxygen sensor; G40—- Hall sensor; G6- 1 and cylinder 2 knock sensors (white plug); G62—- coolant temperature sensor; G6-3,4 cylinder knock sensor (blue plug); G6- throttle potentiometer; G70—- air mass flowmeter; G72—- air temperature sensor; G88— Idle throttle potentiometer; J17-fuel pump relay; J220-control unit; J338—- throttle body; N30-the first cylinder injector; N31-second cylinder injector; N32-third cylinder injector; N33-fourth cylinder injector; N80—- activated carbon canister solenoid valve; N152-ignition coil; P- spark plug plug; Q- spark plug; S- additional fuse (30a); S5- fuel pump fuse (10a); S 17- control unit fuse (10a); V60- idle speed controller; —Engine ground point (near the engine control unit); -Ground connection between sensor and control unit; —Star grounding socket on the left side of the central junction box. Master the characteristics of specific circuit diagram. Compared with other models, this circuit diagram has certain characteristics. It is not only used to represent the circuit trend of the main components in the automobile electrical system, but also can represent the structure of the electrical circuit. Its main features are as follows: 0 1 control the circuit in turn according to the same system. The whole circuit is arranged vertically from left to right, and the circuits of the same system are put together in a certain range in the whole circuit diagram to form a partially complete control system. The serial number at the bottom of the circuit diagram is convenient for maintenance personnel or users to find the position of each electrical component on the circuit diagram. The four horizontal lines at the top of the circuit diagram are used to represent molded copper sheets pressed into the plastic tray of the central junction box. Among them, three are the live wires leading into the junction box for different purposes, and one is the ground wire. The line marked "30" is a constant line, which is directly connected with the positive electrode of the battery; The reference number "15" is the live wire of the small-capacity electrical equipment controlled by the ignition switch, which is led out from the terminal of the ignition switch 15; Reference number "X" is the live wire of large-capacity electrical equipment controlled by unloading relay. Only when the contacts of the unloading relay are closed (the unloading relay is controlled by the ignition switch to reduce the current passing through the ignition switch and protect the ignition switch) can the current of the "30" line be introduced into the "X" line; The reference number "3 1" is the grounding wire, which is connected to the grounding point of the bracket of the central junction box. The whole circuit has almost no twists and turns. For some electrical equipment with complex lines, in order to make them organically connected without destroying the verticality of drawings, the method of number disconnection is adopted to solve it. For example, draw a small square at the end of the upper part of the circuit above the circuit number "45" at the bottom of the circuit diagram, and the internal number "50" means that the lower part of the circuit should be found at the position of the circuit number "50" at the bottom of the circuit diagram; Similarly, the lower half of the circuit has a small box at the beginning of "50" with an internal number of "45", indicating that the upper half of the circuit should be at the bottom of the circuit diagram with a number of "45". Through these four numbers, the upper and lower sections of the same circuit drawn in different positions are connected. Unified representation of 05-wire connection plug. The connecting plugs in the line are uniformly coded with the letter T, and the next number indicates the number of holes on the plug and the hole serial number corresponding to the connecting line. For example, T4/2 means that the plug has four holes, and the corresponding jack number of the connecting wire is 2; T80/7 1 indicates that the plug (T80 is the connecting plug on the electronic control unit) has 80 holes, while the part above the fifth horizontal line in the upper circuit diagram indicates the equipment and wires installed in the central junction box. For example, in the figure, J 17 is the fuel pump relay, and the number in the small box above is 2, indicating that the relay is inserted in the No.2 position on the front panel of the central junction box. There are 2/30, 4/86, 3/87 and 6/854 groups of numbers around relay J 17, where denominators 30, 86, 87 and 85 refer to the numbers of four pins on the relay, and molecules 2, 4, 3 and 6 refer to the four jacks corresponding to position 2 on the front panel of the central junction box. Another example is S5, the fuel pump fuse, which is located at the fifth position on the right side of the fuse installation position under the front panel of the central junction box, with rated current 10A. Codes d, n, p, e, etc. The connector number on the back of the central junction box is marked on the fifth horizontal line of the upper circuit diagram, and the number after the code indicates the socket position of the wire connected to the connector. For example, E 14 means the 14 th socket on the connector e, and n means that the connector has only one socket. Similarly, D23 and D 13 represent the No.23 and 13 sockets of connector D, respectively, and the wires with the same codes on the contacts are all on the same vehicle. The circuit diagram shows the grounding mode and location of electrical equipment. The horizontal line at the bottom of the circuit diagram represents the grounding wire, and the grounding end of the line is marked with circled digital codes, such as,, etc. Indicates the location of the grounding point. Refer to the legend of the grounding part of each code in the circuit diagram. It can be seen that in the car, not all electrical equipment is directly connected to the metal car body and grounded, some are grounded through grounding sockets, and some are grounded through other electrical equipment or electronic equipment. Some circuit diagrams are colored, so the wires in the circuit are not color coded. Use Chinese characters or English letters to indicate the uncolored conductor color on the circuit diagram. After clarifying the above characteristics of Santana circuit diagram, it is not difficult to read this circuit diagram according to the general reading essentials of circuit diagram. Reading essentials of two general circuit diagrams 0 1 Comparison of legends and graphic symbols Be familiar with the names, positions, quantities and wiring of related parts in drawings. For example, in the above picture, G6 is the fuel pump, J 17 is the fuel pump relay, and S5 is the fuel pump fuse (10A). One end of the fuel pump is connected to the output end of the fuel pump relay J 17 through the fuse S5, and the other end is connected to the star grounding socket on the left side of the central junction box. Analyze the circuit according to the loop principle. Any circuit should be a complete electrical circuit, including power supply, switch (or fuse), electrical equipment (or electronic circuit), wires and connectors. It will be grounded from the positive pole of the power supply to the electrical equipment through wires and switches (or fuses), and then return to the negative pole of the same power supply. Take the fuel pump as an example. Power is supplied to the fuel pump (motor) G6 from the positive battery ("30" power cord) through the closed fuel pump relay contact and fuse S5, and then to the negative battery through the star-shaped grounding socket on the left side of the central junction box. Pay attention to the state of the switch or relay in the circuit. Most electrical equipment or electronic circuits realize different functions by forming loops or changing loops through different states of switches (including electronic switches) or relays. For example, the circuit of the fuel pump G6 can only be formed when the fuel pump relay contact is closed, and the condition for the fuel pump relay contact to be closed is that the relay coil is conductive. Similarly, it can be seen from the circuit diagram that the relay coil of the fuel pump can form a loop through the grounding point in the electronic control unit J220 only when the triode which plays the role of switch is turned on. Tip: For the circuit using multi-gear ignition switch or combination switch, you should also pay attention to the following points: How does the battery (or generator) current reach this switch, whether it passes through other switches or fuses, and which terminal of the switch is the live wire connected to? The multi-gear switch has several gears. Several contacts in the switch act simultaneously or separately. Which electrical devices are turned on or off in each gear? Which switch or B constitutes the single-wire system of automobile circuit, each circuit load is connected in parallel, and two power supplies are connected in parallel, which provides convenience for disassembling and reading the whole automobile circuit. The whole vehicle circuit can be analyzed one by one according to each sub-circuit that constitutes the automobile electrical circuit. Tip: For each sub-circuit, you can also read each sub-circuit. The electronic control system circuit can be divided into engine electronic control system, automatic transmission electronic control system, anti-lock braking electronic control system and other circuits. Engine electronic control system can be divided into different circuits such as gasoline injection control, ignition control and emission control.