A 2004 production of imported Touareg 4.2, mileage of 70,000 km, the user reflects the car there are the following symptoms: as long as the ignition switch, the radiator electronic fan on the high-speed operation; oil temperature indicator alarm; engine failure warning light Call the police. After consulting the user, that the car had just recently had an accident, then crashed the front bumper and headlamps, but did not damage the line and the engine any parts. The vehicle is used within 2 days after the repair are normal, but then when the vehicle traveled a large impact on the road, the instrument panel on the oil temperature warning lights and engine failure warning lights at the same time lit, had to stop. When you turn on the ignition switch, the electronic fan will turn non-stop, and the air conditioning is no longer cooling, but the user can not determine the fault warning light alarm and electronic fan often turn at the same time.
    According to the user to reflect the situation, I think the failure of the car should be divided into two kinds of conditions for diagnosis and maintenance. ① engine oil temperature, engine failure warning lights and electronic fan failure is not happening at the same time, then troubleshooting at least two aspects need to be considered: First, warning lights, should focus on checking the oil temperature sensor itself and its line; the second is to check the electronic fan control section. ② oil temperature, engine failure warning lights and electronic fan failure occurred at the same time, then the problem may be out of several faulty component power supply lines and ground lines, find the fault should focus on checking the common connection points of several components.
    According to the above ideas, I decided to first exclude the oil temperature, the engine fault warning light alarm problem.
    The VAS5051 detects the engine electronic control system, the results found the following fault meaning of the fault code: oil / oil temperature unreliable signal; activated carbon tank solenoid valve N115 short to the ground or open circuit; activated carbon container electromagnetic Valve N80 short to the ground or open circuit; fuel system to diagnose the pump to the ground short circuit or open circuit. Although the fault code is found, but according to the meaning of the relevant fault code, I believe that several electrical equipment at the same time the probability of damage is very small, so basically determine the instrument alarm is caused by line problems. To this end, I log on the public company to provide electronic information service inquiry system (ElsaWin) query the car circuit diagram, Sure enough, and the author reasoning exactly, all the failure of the electricity supply equipment are provided by a 10A fuse. After inspection, the fuse has been burned.
    After the replacement of a new fuse, just turn on the ignition switch the fuse was burned, which can determine the line to the ground short circuit situation. In our daily maintenance, the situation encountered in the general short circuit there are two: First, the internal short circuit to the ground, the second is the line to the ground short circuit. For the sake of inspection convenience, the author decided to use the method from the line in turn disconnect the components to determine whether the internal short-circuit components. The specific method is: the ignition switch off, the multimeter placed in the break position, the multimeter of the two table pen connected to one end of the fuse supply, the other ground, and then cut off the line in turn related The component looks at the display status of the multimeter, and the multimeter is turned on. When the high pressure sensor G65 (Figure 3) is disconnected, it is found that the plastic plug of the sensor is broken, causing the 2 terminals of the plug to protrude and the metal piece of the fixed plug just shorts the 2 terminals. Will this be the problem that led to the failure of the car? After the plug is processed, the multimeter is shown as off. Installed after the fuse test, three kinds of fault phenomena are gone.
    So why does the car appear three kinds of fault symptoms? Since the fuse S10 is burned when the power supply line of the high pressure sensor G65 is short-circuited, the corresponding electrical equipment connected to the fuse does not work due to power failure. When the instrument control unit can not receive the signal supplied by the oil level / temperature sensor G266, the red oil warning lamp is lit. When the activated carbon tank solenoid valve 2 (N115) and the fuel system diagnosis pump V114 are short to the ground, the engine The control unit that the system problems, then lit the engine failure warning lights; when the two cooling fan control unit power supply after the break, control the cooling fan relay contacts closed, the fan began high-speed operation (protection function).