A Chery SQR716ES car with a distance of about 128 thousand km. The car was repaired to a small car repair factory because of the damage to the front left part of the car body. The accident partially repaired the car after the accident, but there was a failure to start. The 4S shop nearby was asked for help because it could not be excluded. Fault diagnosis: the maintenance technician has learned from the maintenance personnel of the factory that there is no serious obstacle to the engine part of the traffic accident. Only several wires in the engine main line are broken, and the electrician will be able to start the engine occasionally after the wire has been banded and broken, but the idle speed is unstable and the exhaust pipe is smoked when the engine is accelerated. The engine can't start. First check the ignition system. Pull off the cylinder line of the 1 cylinder and start the engine test fire. No high-voltage spark occurs. The decoder enters the engine control system, and the decoder display system is normal and no fault. This basically eliminates the possibility of sensor and its line failure. The engine uses a non electric electronic ignition system. Each sub cylinder line is connected directly with the ignition module. After the engine ECU receives the signal from the first cylinder on the crankshaft position sensor, the best ignition instruction is issued in accordance with the ignition sequence of the cylinder. Because the crankshaft position sensor is the important basis for engine ECU to control ignition and fuel injection, it is necessary to make a careful inspection. The crankshaft position sensor of the vehicle is a Holzer effect type mounted on the flywheel housing at the front end of the transmission. When the maintenance technician is prepared to measure the signal value of the sensor, the plant power. It is reflected that the power supply, iron lap and signal output of the sensor are normal, and say that if the signal is not normal, the sound of the fuel pump relay should not be heard when the engine is started. To verify the electrician's condition, when the engine is started, the maintenance technician keeps his ears near the fuel pump relay, as the electrician said. So the maintenance technician also concluded that the crankshaft position sensor had a normal signal to the engine ECU. Since the crankshaft position sensor is transmitted to the engine ECU, what are the factors that affect the high pressure fire? From the service department of the factory, they also learned that they borrowed 1 normal Chery cars from the same model, and interchanged the ignition module of the two cars, the engine ECU and the crankshaft position sensor, and the failure phenomenon was the same, and it was proved that all the components of the fault car were good. It is considered that the engine can not be started after the collision, and the main beam of the engine has been sorted out because of the damage, and the phenomenon of short circuit or circuit breakage is doubted. But after careful investigation, this possibility is excluded. Measure the power supply terminal voltage on the ignition module and turn it to 12V after switching on the ignition switch. The troubleshooting has entered the deadlock, so the maintenance technician reorganizes the diagnostic ideas, and again considers that the engine cannot start after the collision, and decides to check the engine outside to see if there is any deformation. When inspecting the flywheel housing, it is found that the flywheel housing has been deformed and the deformation is located at the installation point of the crankshaft position sensor. Due to the deformation of the flywheel shell, the signal of the position sensor of the crankshaft was mismatched. When the engine ECU judged the signal error, it sent out the signal to stop the ignition, thus causing the failure of the engine to start. After replacing the flywheel shell, start the engine test run, the engine starts smoothly, and the idle speed is stable, and the acceleration is good. The above fault is completely eliminated.