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A 2006 mile Shanghai Santana car with a mileage of about 70 thousand km and equipped with BSA engine. The owner enters the factory for repair: occasionally, there is "air throttle" in the running (when the accelerator pedal is stepped up, the engine speed is raised and the speed is not raised). After taking the car: first, verify the failure phenomenon. The road test nearly 10 min also did not appear the car owners reflected the failure phenomenon, engine acceleration, idle speed smooth, the clutch work is also normal, no "skidding" phenomenon. Carefully inquire about the owner of the car, in order to find the law of the failure, such as whether there is a difference between the refrigerator and the heat engine, the fault occurs when the start shift or normal driving, the engine will be extinguished when the failure occurs, and there is no abnormal alarm on the dashboard. After further communication with the owner, it is known that there is no law for the occurrence of the fault. It is possible to appear at any time. When it fails, the speed of the accelerator pedal is stepped down, and the speed of the car will not change, but the speed of the car will suddenly be normal and the car will suddenly go forward. In the new step, the engine can be restored to normal, but the engine idle speed is very stable, and there is no abnormal alarm light on the dashboard. The fault has lasted for more than 3 months, and has changed the throttle body assembly, the intake manifold absolute pressure sensor, the fuel pump and its control relay, the ignition control module, the high. The pressure line and spark plug are also interchanged with the engine of a normal vehicle. When you understand these situations, it's really tricky to feel trouble. Then the fault detector reads the fault information in the engine control module, displays the failure code storage, reads the data flow, and shows the normal data in each condition of the engine. Because the engine is all right now, we have to do some basic checks first. According to the circuit diagram, the power supply of the engine control module, the bypass line, all the lines connected to the throttle part, the wiring of the ignition module, and the control line of the fuel pump are connected, and all the results are normal. The car was forced to carry on the road test, and the fuel pressure gauge was attached to the former occupant side seat, and the change of fuel pressure was monitored in real time, and the fault detector was attached to capture the change of real time data when the fault occurred. The test is nearly 40 min, and the above failures appear. The failure phenomenon, as the customer said, will speed up the pedal, but the speed will not change. In order to see the changes of fuel system pressure and related data flow in time. I have been stepping on the accelerator pedal, not simulating the failure state of the accelerator pedal and then stepping down. Instead, I look at the fuel pressure gauge with my colleagues, and the result shows that the fuel pressure is normal; it continues to look at the relevant data flow, and there is no obvious exception. The fault persists about 10s, engine speed. All of a sudden, the engine went up and then the engine returned to normal. The initial feeling is like insufficient fuel supply. Since the fuel pump is new and the fuel pressure is normal, it is a problem with the fuel filter, but the colleague reflects that the car has just finished the maintenance and changed the fuel filter. Then we continued the test, and not long after the failure to repeat again, this time, we found a rule, that is, when the fault occurs, the accelerator will step on the pedal to the end. Although the engine speed does not rise, the idle speed is very stable, but the idle speed is obviously higher, the instrument shows the speed of about 1200 r/min, and the fault detector shows 1196 r/ Min, check the throttle data and always display idle speed. After obtaining these information, further analysis is carried out, and the reasons for the failure are as follows: one is to accelerate the pedal position sensor fault, the signal is unstable; two is the new throttle controller assembly problem; three is the engine control module. So the car opened back to the factory to continue to repair, considering the throttle is new, the engine control module has been interchanged with the normal car, so the problem is concentrated on the accelerator pedal position sensor, but the replacement accelerator pedal position sensor test, the failure is still. According to the analysis of the failure phenomenon, the engine control module seems to be in the emergency operation mode when the feeling fault occurs. It keeps the engine from extinguishing and the idle speed is maintained at 1200 r/min. Will the engine control module receive the wrong signal and implement the protection operation mode? Since all the related components are normal and the lines are normal, the only brake light switch that has not been checked and also affects the control of the engine module is the only one, because the car adopts the electronic throttle (EPC). If the engine control module receives the wrong brake signal, the above fault may occur. Troubleshooting: after a long circuit test after replacing the brake light switch, the above fault never happened again. After the phone call back, the car has been running normally, so that the fault completely eliminated. Fault summary: the engine control module, in addition to receiving the throttle position, acceleration pedal position and other signals, also receives the wrong brake signal of the brake light switch when the vehicle fails, and the engine control module can not identify the actual condition of the current car, so the default emergency operation mode is adopted.