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The FAW Volkswagen Teng 1.8T distinguished car with a mileage of about 46 thousand km in 2012. User response: the vehicle can not be turned off with one key start, and at the same time, it is accompanied by failure of loudspeaker and headlamp cleaning. Inspection analysis: first, the maintenance personnel connect with the fault diagnosis instrument VAS6150A to check, read the fault code 276412 - enter / start approval button electrical fault (static); read the ignition switch terminal state, find S connection, 75 (X) connection, 15 connection, 50 close; check the J393, J942, and E408 wiring harness plug. Connectors, no loosening, damage and corrosion; check J393, J942, J519 and J527 control unit coding, normal. There is a common feature of the 3 failure phenomena: the horn does not sound, the headlights do not work and the one button can not be flameout. That is, the signal is passed through the J527 control unit, so the maintenance personnel change the new J527 and re code it, and the result is still in trouble. The failure of loudspeaker and headlight cleaning is caused by J519 damage. Referring to the experience of repairing this kind of fault before, the maintenance personnel power off the battery, after the recovery test, the horn, the headlight cleaning and the one button start function normally, but can not be extinguished. In order to find out the cause of the trouble as soon as possible, the maintenance personnel borrowed a similar model and configuration for trial driving. Through careful observation, one key start function can be used normally, one key start button background light L76 is bright, if the light is not bright, the one key start function also fails, according to this consideration may be the startup button failure, because the L76 light is integrated in the E378 one key start device open, so replace one key start press Health, the result is still. In the inspection of the maintenance personnel, the T32g/2 terminal of J942 (terminal and engine start control system control unit) is found to have 12V voltage when the vehicle is not started, and the test drive is in such a state that the terminal is not charged. Dial the T32g/2 terminal, the L76 button light is lit, then the one button start function is resumed. Read the circuit diagram analysis, the T32g/2 terminal is used to monitor the key insertion signal. When the key is inserted, the terminal generates S contact voltage signal. When the key is pulled out, the S contact is broken and automatically switched to a one button start signal. According to the above principle, it is judged that the line between the T32g/2 terminal of J942 and the T16f/16 terminal of the ignition switch between the positive pole short circuit or the electronic ignition switch internal mechanical fault, check the line without fault, and finally judge the fault of the electronic ignition switch itself. Troubleshooting: replace electronic ignition switch D9, troubleshooting. Review summary: the focus of this troubleshooting is to understand the function of the T32g/2 terminal in J942. This terminal is a S contact. When the S contact is disconnected, the disconnected signal is passed to the J942 to enter the one key start function; when the S contact is connected, the closed signal is passed to the J942, the one key start function fails, and the mechanical key can be started. Vehicles. In the process of maintenance, only the function of the S contact signal is fully understood, and the results of the normal vehicle S contact signal voltage under 2 kinds of starting modes are measured by contrast, and the fault points can be found quickly and accurately.