Fault caused by sensor characteristic change of th

2022-08-25
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Faults caused by changes in the characteristics of sensors in electronically controlled vehicles

fault analysis caused by changes in the characteristics of coolant temperature sensors

coolant temperature sensors are composed of negative temperature coefficient thermistors that are very sensitive to temperature changes. The resistance has the characteristic that the higher the external temperature is, the smaller the resistance value is. According to this characteristic, the change of resistance value is used to detect the temperature of coolant, and this signal is transmitted to ECU as an important correction signal of fuel injection quantity

for the normal use of the coolant temperature sensor, customers require an English report with a range of -30 ℃ ~ 120 ℃, and the corresponding output voltage value is 0.3V ~ 4.7V. When ECU detects the output voltage signal beyond this range, it can be judged that the sensor circuit has failed. At this time, on the one hand, the self diagnosis system lights up the fault indicator and memorizes the fault code, on the other hand, it provides a fixed value of the 80 ℃ coolant temperature pre memorized in the EUC memory, which is used to continue to control the engine operation and prevent the vehicle from driving due to abnormal signals. However, when the characteristics of the coolant temperature sensor change, that is, the voltage signal sent by the sensor to the ECU is inconsistent with the change of the coolant temperature, and its value does not exceed the range monitored by the ECU, the ECU will make a wrong judgment on this abnormal signal. As a result, the fuel injection signal is abnormal and the vehicle working condition is poor

an example is a 99 Santana era Superman car. The fault phenomenon is that it shivers at idle speed, and there is no fault code

since there is no fault code, it is impossible to determine the location of the fault. Regularly replace the oil suction filter and filter element. According to the fault phenomenon, check the possible mechanical faults, and eliminate the causes of throttle carbon deposition and idle speed control actuator blockage

then use the data flow function of vag1552 tester to check the electronic control system. When observing the data value of coolant temperature, it is found that the temperature displayed at idle speed is abnormal, and the data value is unstable, with fluctuations. Press the accelerator pedal to increase the engine speed and load. Observe the rise of coolant temperature and find that the temperature does not rise evenly. Therefore, it can be judged that the operating characteristics of the coolant temperature sensor have changed before the onset, resulting in the inaccurate injection correction signal

test run after replacing the coolant temperature sensor and troubleshooting

fault analysis caused by the change of throttle position sensor characteristics

throttle position sensor converts the opening of throttle valve, that is, the change of engine load, into an electrical signal and sends it to ECU. ECU judges the working condition of the vehicle according to the signal that the plastic proportion of each vehicle is as high as 30% (4) 0%, and corrects the fuel injection quantity in time. If the throttle position sensor has poor working characteristics, it will cause ECU to make errors in judging the current working condition of the vehicle, so that the adjustment of fuel injection volume does not adapt to the vehicle working condition, resulting in failure

an example is a 99 Santana era Superman car. The fault phenomenon is poor acceleration and no fault code

if there is no fault code, the electronic control system may not be faulty, or the electronic control system may be faulty, but the self diagnosis system cannot detect it. Based on this analysis, the fuel pressure is first detected. From the result, the oil pressure of the fuel system is normal. Then the dynamic data flow of throttle position sensor and air flow sensor is checked with the data flow function of vag1552 detector. When the throttle is slowly opened from the idle position to the full open position, the amount of air inhaled and the injection time increase evenly with the increase of the throttle, and everything is normal. When the accelerator pedal is pressed quickly, the data value of intake air volume is normal, but the data value of throttle opening angle changes abnormally. From the idle position to about 45, the data value increases rapidly; The data value increases slowly in the range of 50 ~ 70, that is, the change of the data value lags behind the change of the actual throttle opening angle. Therefore, it can be judged that due to the change of the working characteristics of the throttle position sensor, the sensitivity decreases, and the slow response to the rapid opening of the throttle, the ECU sends wrong instructions, so that the fuel injector cannot quickly respond to the change of the throttle opening, and the fuel injection lags behind, resulting in the slow increase of the engine speed and poor acceleration

replace the throttle position sensor. After road test, the fault disappears

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