How to detect the quality of automobile speed sensor

When the car is driving at a speed of about 40km/h and accelerating to 3000~4000r/min, the pointer of the tachometer will drop sharply to 2000r/min instead of slowly dropping to about 500r/min. But at this time, it is difficult for the car to speed up, so it can be considered that the transmission has entered the shift point.

After checking that the transmission oil level is normal, a road test will be conducted to check the upshift speed. Generally, when the throttle opening of a 4-speed automatic transmission is kept at 1/2, the speed of the 4-speed automatic transmission when it normally shifts from 1 to 2nd gear is 25 ~ 35 km/h.. When shifting from second gear to third gear, the speed is 55 ~ 70 km/h; When shifting from the third gear to the fourth gear (overspeed gear), the speed is 90 ~ 120km/h ... If the acceleration of the car is weak while driving, the upshift speed is obviously lower than the above range, indicating that the upshift speed is too low (that is, the upshift is too early); If the car has obvious shift impact when driving, and the upshift speed is obviously higher than the above range, it means that the upshift speed is too high (that is, the upshift is too late). Figure 1 is the shift diagram of automatic transmission, the solid line is the upshift curve, and the dotted line is the downshift curve. Usually, the relationship between the upshift speed of hydraulic automatic transmission and the throttle opening is curvilinear, as shown in figure1-a; The relationship between the upshift speed of electronic automatic transmission and the change of throttle is stepped.

Too low upshift speed is generally caused by the failure of control system, while too high shift speed may be caused by the failure of control system and shift actuator. When doing the road test of automatic transmission with engine tachometer, we should pay attention to the change of engine speed during driving, which is one of the important basis to judge whether the automatic transmission works normally. Put the car in economy mode, keep the throttle valve in the opening range of 1/2, and the engine speed is lower than 3000r/min during the whole driving process from starting to high gear, usually it can reach 2500~3000r/min when it is about to shift gears, and it will drop to about 2000r/min when it just enters shifting gears; The speed of this car is 20~30km/h in 1-2 gear, but it reaches 80km/h in 2-3 gear. At this time, the engine tachometer pointer actually reached more than 4000r/min, while continuing to increase the throttle, and there was no feeling of entering the OD gear. From experience, the promotion is too late.

The reasons for the late upshift are: improper adjustment of throttle cable or throttle position sensor; Main oil pressure or throttle oil pressure is too high; There is something wrong with the computer or sensor.

There is no throttle line in the automatic transmission of this car. According to the fault analysis, it is suspected that the throttle position sensor is improperly adjusted, which leads to the high upshift speed.