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The mileage is about 176 thousand km, and the 2006 Volkswagen Bora car is equipped with BJH engine. The car's hot engine sometimes starts four or five times to start the car. Fault diagnosis: first, the V. A. G1551 is used to query the fault code, no fault code is stored, and the control unit signals are monitored in the idle state. All the work is normal, and the signal function of each sensor can be considered to be normal. In view of the great influence of the coolant temperature sensor on the thermal starting, the emphasis is on the tracking of the temperature sensor signal of the coolant, and no abnormality is observed in the cold and hot car conditions. Because of accidental failure, it is not easy to detect it. First, the hard start of the hot car is analyzed: (1) the fuel injector is permeated by the injector, and the cold starting condition is not needed to adjust under the hot starting condition. Too much fuel is caused by excessive mixture of gas, which leads to insufficient combustion. If there are more than two cylinders, it may be difficult to start the oil. (2) the temperature sensor of the coolant is accidental (can be excluded); (3) the ignition component is poor in performance, especially the thermal stability is poor; (4) the control unit is poor in performance, especially the thermal stability is poor; 5. Check the ventilation mechanism of the carbon canister without clamping phenomenon, and the electronic control circuit of the carbon canister ventilated engine is normal. The detection of spark plugs, the observation electrode and the seat ring is grey and white, and the phenomenon that the electrode has been blackened by insufficient combustion is not found, and the oil pressure is 250kPa, it is normal oil pressure, and the oil pressure does not decrease in 10min after quenching, thus the oil permeation of the injector can be eliminated preliminarily. In addition, if the ignition component is poor in performance, especially the thermal stability is poor, it also causes insufficient combustion, and it does not seem to match the spark plug combustion state of the car. The most likely analysis is that the fuel pump, the fuel injector, the control circuit of the control circuit, the motor control circuit of the fuel pump and the electronic control circuit of the fuel injector on the control circuit. After many tests, the fault phenomenon has finally appeared. At this time, the normal oil pressure is observed, thus eliminating the failure of the electronic control circuit of the fuel pump and fuel pump. Under the condition of failure to start the car, check the power supply line of the control unit: the T121/3 foot and the T121/62 foot have 11V voltage, and the T121/2 foot is normal to the ground. When the car is starting, the T121/112 foot and the T121/113 foot have pulse voltage output. However, the T121/86 to 88 feet detection can not detect the fuel injection pulse signal. At this time in the failure state of starting the car, pull off the plug of the injector and measure 1 feet without electricity. It shows that the reason of the impulsive signal is not in the engine control unit, but the power supply circuit of the injector, which is known by the circuit Tutu 1, S228 (fuel pump motor fuse), S232 (fuel supply fuse of injector), S243 and S234, etc. The fuse of the engine actuator is controlled by the output end of the fuel pump relay J17, because the fuel pump is working normally, indicating that the output terminal voltage of the fuel pump relay J17 is normal, and further checks that S228, S234 and S243 have electricity when the car is not starting, and only S232 is without electricity when starting the car, and the S232 fuse is checked. This problem can be loosely inserted, so the problem can be locked between the common node A99 in the instrument harness and the circuit fault between the injector S232 fuse. After examination, S232 has poor contact in the fuse box, and the S232 circuit is shown in Figure 2. Due to the loosening of S232, it is easy to produce bad electrical conductivity on the weld line seat. With the influence of tidal gas, the fuse socket is exposed to bad contact because of oxidation, and the resistance of the hot car increases, which will naturally cause the difficulty of even starting. At this time, there is a mixture gas too dilute fault storage in the engine control unit (Ou Fa), which is also caused by no fuel injection. Due to contingency, the fault will be cleared by the control unit after a certain starting frequency, and it will bring some difficulties to the trouble shooting.