The inspection analysis first uses the fault detector to read the fault information, and the fault information is as follows: the voltage of the 5 terminal of the power supply of the engine sensor is low and the voltage of the ECM wire beam sensor is too low. At the same time, it was found that the engine came into a limp home state and restricted the power output. Then start the engine test, found that the engine idle speed is normal, but the accelerator pedal about 30 s, the engine speed immediately up to 3000 R / min, then no matter how to step on the accelerator pedal, the engine speed will no longer rise, completely unlock the accelerator pedal, the engine back to 900 R / min idle state. According to the failure phenomenon, it is preliminarily believed that the accelerator pedal position sensor is opened inside, so the resistance of the accelerator pedal position sensor changes with the accelerator pedal opening change with the multimeter, and the result is found that the resistance is not changed (after that the sensor is not the slip resistance type), it is found that the sensor has found the reason. The barrier point. The analysis considers that the working condition and the use environment of the vehicle are rather bad. The accelerator pedal position sensor is damaged very well. But after the replacement of the accelerator pedal position sensor, the trouble can not be ruled out. Then proceed to check the accelerator pedal position sensor line. The sensor has 6 lines to the engine ECU. After the line numbers are 1404, 1406, 1403, 1484, 1485 and 1486~, the traverse side connectors of the engine ECU and the sensor are pulled out. The conductance of each wire is measured by a multimeter. The wires are normally conducted. The wire harness connector is suspected to be in bad contact, but the wiring harness connector is repeatedly plugged in. After the test, there was no effect. At this time, it is associated that the fault detector indicates that the voltage is low, so check the power supply of the sensor. The accelerator pedal position sensor should have 2 5V power supplies, measure the voltage on the 1404 line, be 5 V, and measure the voltage on the line 1484, but only 1.39 V; then the engine ECU corresponds to the voltage on the output terminal. It is also 1.39 V, indicating that there is no voltage drop in the circuit. The problem is suspected on the ECU of the engine. So the engine EC[J was replaced, but after the replacement test, the trouble remained. Looking up the circuit diagram of the car, it is found that line 1484 has the power supply of the radiator coolant liquid level sensor and the accelerator pedal position sensor when the 1484 line is out of the two lines, which may cause the voltage drop of the power supply. Through the investigation, it is found that the short circuit of the coolant liquid level sensor on the radiator makes the voltage in the No. 1484 line too low, which causes the engine work to be abnormal. Remove the coolant level sensor on the radiator.