Cooling temperature sensor fault analysis

The normal temperature range of the coolant temperature Sensor is -30°C to 120°C, and the corresponding output voltage value is 0.3V to 4.7V. When the ECU detects an output voltage signal outside this range, it can be determined that the sensor circuit has failed. At this time, 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°C coolant temperature stored in advance in the EUC memory, which is used to continue to control the operation of the engine and prevent the signal from malfunctioning. The car cannot drive. However, when the characteristics of the coolant temperature sensor have changed, that is, the voltage signal sent from the sensor to the ECU does not match the actual temperature of the coolant, and the value does not exceed the range monitored by the ECU, the ECU will report an abnormal signal to the ECU. Make wrong judgments. As a result, the injection signal is abnormal and the vehicle operating conditions are poor.

The case of a 99-segment Santana Superman sedan, the fault phenomenon is idle shaking, no fault code.

Because there is no fault code, it is not possible to determine where the fault occurred. According to the fault phenomenon, the possible mechanical failures were checked, and the causes of the failure such as the throttle valve's carbon deposition and the idle speed control actuator's blocking were eliminated.

Then use the AUTOBOSS computer diagnostic instrument to check the electronic control system. When observing the data value of the coolant temperature, it was found that the temperature displayed at idle is not normal, and the data value is unstable and fluctuates. Depress the accelerator pedal to increase the engine speed and increase the load. Observe the increase in 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, resulting in inaccurate injection correction signals.

Replaced the coolant temperature sensor after the test, troubleshooting.

No fault code <br> cases cause the failure judgment <br> characteristic change of the throttle position sensor failure analysis sensor is a throttle position of the throttle valve opening degree, i.e., the engine load change into an electrical signal delivered to the ECU. Based on this signal, the ECU judges the operating conditions of the vehicle and corrects the fuel injection amount in time. If the throttle position sensor has poor operating characteristics, it will cause the ECU to determine the current vehicle operating conditions in the wrong, so that the adjustment of the amount of fuel injection and automotive conditions do not meet, resulting in failure.

Case A 99 Santana Superman sedan, the fault phenomenon is bad acceleration, no fault code.

In the absence of a fault code, there may be no fault in the electronic control system, or there may be a fault in the electronic control system, but the self-diagnosis system cannot monitor it. Based on this analysis, the fuel pressure was first tested. From the results, the oil pressure of the fuel system is normal. The vehicle was then diagnosed using the AUTOBOSS computer diagnostics. The data flow group function was used to check the dynamic data flow of the throttle position sensor and the air flow sensor. When the throttle is slowly opened from the idle position to the fully open position, the amount of air sucked in and the injection time increase as the throttle is opened, and everything is normal. When the accelerator pedal is depressed quickly, the data value of the intake air amount is normal, but there is an abnormality in the change in the data value of the throttle opening angle. From the idle position to the range of around 45°, the data value increases rapidly; in the range of 50° to 70°, the data value increases slowly, that is, the data value lags behind the actual opening angle change of the throttle. It can be judged that, due to changes in the operating characteristics of the throttle position sensor, the sensitivity is reduced, and the responsiveness to the quick opening of the throttle valve is unresponsive, and the ECU issues an incorrect command so that the injector can not respond quickly to changes in the throttle opening degree and the fuel injection is delayed. As a result, engine speed increases slowly and acceleration is poor.

Replace the throttle position sensor. After the road test, the fault disappears!