The 2004 Volkswagen Passat 1.8T limousine with a mileage of about 190 thousand km. The car EPC alarm light is often bright, and the other maintenance stations have not been repaired many times, then to my station to repair, replaced the engine harness and instrument harness, generator, control computer, throttle and acceleration pedal, when the EPC alarm light was not bright, but a few days later back to the factory. Fault diagnosis: use a special diagnostic instrument to read the fault code: 18047P1639 035 throttle, pedal position sensor 1, 2; G79, G185, the signal is not clear, and the same as the fault code for the first repair. Through the test, the computer to the throttle power supply line, the green / purple line voltage is 5V, the red / purple line voltage is 3V, the Zong / purple line voltage is 3V; the G79 accelerator pedal acceleration sensor 1 (gray line) voltage is 5V, the G185 acceleration sensor 2 (yellow / Purple line) voltage is 5V; the other signal lines are normal, indicating the throttle, computer, acceleration pedal There is no problem with the communication between them. Since the results of the relevant components are all normal, we need to consider whether the engine sensor signals are abnormal. One by one, the sensor was disconnected and tested repeatedly. It was found that only after the oxygen sensor was disconnected, the failure phenomenon disappeared. Before replacing the post oxygen sensor, the engine data were read, thirty-sixth groups were shown as "0AV" and the thirty-seventh group was displayed as "21.1% 0.44". After replacing the new oxygen sensors, the engine data were read again, the thirty-sixth groups were "0.1 to 0.9V", and the thirty-seventh groups were "37.6%0.1 to 0.8V". Comparing these two sets of data, we can see that the signal of the old post oxygen sensor is lagging behind. After careful examination, it was found that the original rear oxygen sensor of the vehicle was "sub factory parts". According to the experience, the delay of the signal of the oxygen sensor has been encountered, but it has not affected the EPC, but the exception of the car may be due to the abnormal signal of the non specification auxiliary factory parts, causing the internal signal of the engine computer and causing the EPC failure. After replacing the oxygen sensor, the fault is completely eliminated.