Failure phenomenon: a 2000 annual production Volkswagen Santana 2000 sedan, equipped with 01N four-speed automatic transmission, mileage of 110,000 km. The car in the field on the way in the transmission of oil sump damage, resulting in transmission loss of oil and burn. After repairing the local repair shop, maintenance personnel found no high speed gear, and accelerated response slow.
    Troubleshooting: Connect the fault diagnosis machine V. A. G1552, input 02 automatic transmission system, display the temporary fault code "transmission speed sensor signal is too weak", measured at the top of the transmission sensor on the left side of the 60Ω, is a normal range. Suspected the possibility of the sensor failure is small, so the focus of the inspection on the line, when found in the transmission of the tail of the two plugs, found a plug wrong phenomenon.
    The design of the vehicle line to consider the convenience of maintenance checks, all electrical connection plugs are basically the same, such as plug can not be assembled, if there are two sensors in the electrical system, the sensor connection plug pin exactly the same, Then with different colors or the length of the connection wire to distinguish, the car is such a class.
    For the transmission speed sensor and speed sensor of these two sensors, they are from the structure, shape point of view is exactly the same, are electromagnetic, with the two feet plug, and the same resistance, are 60Ω. But their role is not the same. The transmission speed sensor is located on the left side of the top of the transmission to detect the speed of the large sun gear in the planetary gear set. The control unit uses this signal to detect the shift action, perform the ignition advance angle of the engine, and control the multi-plate clutch at the time of gearshift. If this sensor fails, then the transmission control unit will switch to the emergency running state, emergency operation in the 3 block. And the vehicle speed sensor signal is obtained from the pulsator of the input gear, and the transmission control unit uses the signal to determine the shift timing and the slip amount of the control torque converter.
    Transmission speed sensor to harness pin should be black, the speed sensor to the wiring harness should be brown, due to maintenance personnel ignored, causing the transmission in the emergency mode and no high speed gear. Will be two plug on the transfer test, everything is normal.