Detection methods and related research of automobile instruments

    No matter how complex the automotive electronic instrument is, it is composed of a traditional transmitter (such as a cooling water temperature switch, a fuel tank float variable resistor, etc.) and a solid-state circuit with the same function as an electromagnetic display device (analog instrument). The microprocessor installed between the transmitter and the display device is used to interpret the signal from the transmitter and calculate the actuator signal sent to the display device. The display device can be a light-emitting diode (LED), a liquid crystal display (LCD) or a cathode ray tube (CRT). The actuator signal from the microprocessor is a voltage pulse that makes the display device work according to the design requirements. When repairing automotive electronic instruments, just like electromagnetic instruments, you should first ensure that the engine is in a completely normal condition. Before assuming that some electronic instruments are faulty, you should first test the engine condition. General test of the system In addition to all the functions of traditional instruments, some electronic instruments on modern cars are equipped with an accumulated time table (E/T), a driving computer or an electronic navigator on the electronic dashboard of some cars, and some are also equipped with more than 10 voice warnings and information prompts or provide more than 20 different voice warnings and visual information according to the equipment of the car. Generally, the display device of each electronic instrument system is mostly independent, but in some new models it may be combined with other electronic functions. Due to the rapid development of the automotive instrument industry, its display functions and operating procedures may be different every year, and even the same year and model of cars may use different systems. Since some cars have more than one instrument manufacturer, the same instrument display device on the car may also use different circuits. Therefore, when diagnosing faults in the electronic instrument system, it is necessary to test according to the diagnostic procedure table of the automobile manufacturer.

　　The electronic instrument system of the automobile is equipped with a self-diagnostic program or test process, which can find problems with the instrument system and store the faults as fault codes or display them in text. Different systems may use different circuits and diagnostic programs. The electronic instrument system of Chrysler automobiles uses its self-diagnostic program to check the display function of the instrument. Through the detection of the self-diagnostic program, it can be determined whether the cause of the problem is inside the circuit of the system or outside the instrument. When the headlight switch is turned on or the rheostat that adjusts the light brightness is turned, if the instrument display does not dim, then: 1 Check the fuse of the headlight circuit. Check whether the connection of the line from the headlight switch to the instrument panel is loose or faulty. If the engine tachometer does not work, check the connection of the line from the instrument panel to the speed sensor . If the engine is electronic fuel injection, the connection of the instrument panel to the electronic fuel injection power module should also be checked. Replacement of display device In most cases, the electronic instrument panel is replaced as an assembly during repair, and the procedures are the same as those for traditional instrument panels. If a meter is broken, the entire instrument panel must be replaced. The trip computer and other electronic display devices are also only replaced and repaired. If the electronic instrument system uses an odometer memory chip, the chip must be removed from the broken instrument panel and installed in the new instrument panel, just like removing the programmable read-only memory (PROM) from the broken electronic control module (ECM) and installing it in the new module. Different countries have different regulations on replacing the failed chip with a new odometer memory chip. Some countries require the original mileage to be posted on the door pillar meter, and some countries program the chip to display the mileage of the original chip. The replacement method of the odometer memory chip will be different for different manufacturers. Chrysler cars need to use a special tool to clamp and pull out the chip. While gently pulling the chip upward, shake it left and right. The replacement steps are as follows: Remove the instrument panel and place it face down on a clean workbench with the bottom of the instrument panel facing the maintenance personnel.

　　Gently press the ear-shaped lock of the odometer chip inspection hole cover toward the center of the inspection hole cover to swing the hole cover open. The conspicuous notch on the integrated circuit chip installed under the hole cover should face the left (the bottom of the dashboard faces the maintenance personnel), and the new chip must be installed in the original position. Clamp the chip with a special tool and remove it from the dashboard. If the chip is not installed in a new dashboard immediately, write the vehicle identification number (VIN) and mileage on an envelope and store the chip in it. Before installing the chip in the new dashboard, check the chip's feet to ensure that they are straight and perpendicular to the chip body.