Fault phenomenon: a Passat 1.8T diesel vehicle, equipped with BPZ engine, has a mileage of about 400 thousand km. According to the driver, the car was unable to accelerate at high speed. The fault diagnosis test run found that the speed was before 80 km / h. The vehicle accelerates normally; if the speed reaches 80 km / h, the vehicle will continue to accelerate. A fault record with "boost pressure limitation" is detected by the fault detector. The exhaust gas turbocharger is replaced according to the vehicle condition and fault information. The acceleration performance of the vehicle is improved, but the speed of the vehicle can only reach 100 km / h, and the fault detection instrument is stored in the fault record of "exhaust gas recirculation flow". Remove the exhaust gas recirculation valve, then block 2 interfaces, remove the fault code and test the car, the fault is still, and the fault detector stores the fault record of the "low voltage of the air flow sensor". Check the air flow sensor data for 240m coffee (according to the engine speed of 800 R / rain, about 32g/s), normal. The air flow sensor is powered by the fuse $231 by the No. 15 power supply line, and uses a multimeter to measure the voltage of the terminal 2 and terminal 4 to 12 V and 5 V, respectively. In order to completely eliminate the air flow sensor failure, change the air flow sensor after the test, the fault is still, and the fault detector store the "exhaust gas recirculation valve" record of failure. The fault record has been changing, and the fault diagnosis is deadlocked. Reorganize the maintenance idea. Under the static state of the vehicle, the acceleration pedal is urgently stepped. When the engine speed reaches 5000 R / min, the pressure pressure is 1.8bar (1bar=100 kPa), which is in accordance with the test data of the normal vehicle. The maximum pressurization pressure of Passat 1.8T diesel engine can reach 2.2 bar, once the pressure is exceeded. It will be restricted by the pressurized pressure limiting valve. If you want to know if the boost pressure of the car can reach 2.2bar, it must be measured in the road test. In order to prevent the pressure difference of the booster pressure sensor from affecting the measurement results of the boost pressure, it is decided to replace the booster pressure sensor first. However, when replacing the boost pressure sensor, it is found that the fixed bolt on the boost pressure sensor is not screwed, and the boost pressure sensor is slightly loose. The fault excludes the fixed bolts on the pressurized pressure sensor to fasten the rear test, and the vehicle accelerates without retardation when the vehicle is at high speed. The speed can be promoted to 140km / h smoothly, and the fault is excluded. When the fixed bolt on the pressure sensor is loosened, when the pressure pressure is below 1.8 bar, the fixed force can still be countered with the pressure pressure. The contact surface between the pressurized pressure sensor and the inlet pipe can still be sealed and the vehicle accelerates normal; when the pressure pressure exceeds the 1.8bar contact surface, there will be a gap. The pressurized air leaks from the gap, causing the pressure pressure to not continue to rise, and make the mixture thicker, so the vehicle speeds up when the vehicle is at high speed; and once the pressurization pressure drops to 1.8 bar, this kind of inflection leak will disappear, so the vehicle accelerates normal at low speed.