Fault phenomenon
    1993 Toyota Camry 2.2-liter engine, model 5S-FE, automatic transmission model A-140E. There is a gearbox shift light "ODOFF" lit, followed by automatic transmission lock in the 2 block.
    Fault Judgment and Analysis
    We must first understand the working principle, according to the principle and fault phenomenon targeted to repair, so as to do more with less, less detours.
    A-140E gearbox is an electronically controlled automatic transmission, gearbox shift and torque converter lock are controlled by the gearbox electronic control unit (ECTECU). In this model in the engine electronic control unit and gearbox electronic control unit is made a whole. The transmission electronic control unit receives various input element signals, and uses these signals (mainly the throttle position sensor signal and the vehicle speed sensor signal) to control the first and second shift solenoid valves and the torque converter lock solenoid valve. Electronic control unit has a self-diagnosis system, electronic control system failure, the electronic control unit will store the fault code. A-140E gearbox electronic control unit of the main input components are:
    · Pattern selection switch (PatternSelectSwitch)
    · Parking / neutral (P / N) position switch (Park / NeutralPositionSwitch)
    Throttle position sensor (ThrottlePositionSensor)
    · VehicleSpeedSensor
    Brake light switch (BrakelightSwitch)
    · Oversight switch (ODSwitch)
    · Water temperature sensor (CoolantTemperatureSensor)
    The output elements are:
    The first shift solenoid valve (No. Saolenoid)
    A second shift solenoid valve
    Lock-up solenoid valve
    Then the transmission control system for fault code read. The detection system has a fault code 61, meaning the second speed sensor. Clear the fault code, check the gearbox oil quality, meet the requirements, the gearbox level is also within the specified range. Check the throttle cable and shift lever cable, and slightly adjust. Then the test, gearbox failure still exists. After a long distance, the gearbox fault light "ODOFF" starts to flash, the gearbox enters the fail-safe mode (Fail-safeMode), locked in the 2 block. Read the fault code, or 61.
    This model of the second speed sensor structure for the reed tube, is a contact with the switch components. When the magnetic field changes, the reed switch is turned on or off. The detection steps are as follows: the roof lift, so that the front wheel can be free to turn. Unplug the second sensor on the wire plug, the multimeter placed in the ohm file, with a multimeter to detect the work of the speed sensor. When turning the front wheel, observe the multimeter value for a while, turn it off for a while, keep changing. This shows that the gearbox internal drive speed sensor work components and the speed sensor itself is no problem. Check the line between the second speed sensor and the gearbox electronic control unit, and no fault is detected.
    Is the gearbox computer is faulty, to the shift solenoid valve issued a wrong order? In order to observe the control of the transmission control unit, two automotive instrumentation light bulbs (in order not to affect the normal operation of the solenoid valve, should use low-power bulbs) were connected in parallel on the two shift solenoid valve, and the lamp placed In the cab for observation. When the road test, the two bulbs or light or off, change frequently, there is no law; gearbox shift also with the light bulb or dark synchronization; when the "ODOFF" fault light is lit, the parallel in two The gear on the shift solenoid valve remains in the steady state, the gearbox into the failure protection mode, locked in the 2 block. It can be judged that the shift solenoid valve and its associated circuit are normal.
    Is it really a problem with the computer? Is there any other reason? As a result of no time with the same type of computer replacement test, maintenance in trouble. Some technical staff said that the computer should be a problem, buy a computer installed will be good; there are some people say that the transmission removed to break down, check the gearbox there are no mechanical problems. I insist that there is no sufficient evidence that the computer is bad, do not easily buy a computer or remove the transmission to break down, so as to avoid unnecessary losses.
    Or from the 61 fault code analysis to start. This gearbox shift signal is mainly the speed sensor and throttle position sensor signal. Now assume that the computer and gearbox mechanical parts are good, then you can certainly shift the input signal problems, resulting in gearbox shift is not normal. By detecting the input signal of the throttle position sensor, it is found within the normal range. Is the problem still in the speed sensor? Moreover, there are 61 fault code. Although the second speed sensor has signal output, but the output signal is normal? Through the further study of the second speed sensor, its output waveform should be square wave. The oscilloscope connected to the second speed sensor, the road test, found that the sensor output waveform chaotic, simply do not see the square wave. It is certain that the second speed sensor is damaged.
    Troubleshooting
    After changing the second speed sensor, through the oscilloscope observation, the second speed sensor output is the standard square wave, and with the increase in speed, the waveform frequency also increases. Everything is normal, the customer is satisfied.