Maintenance case of fault light on BMW E70 acceleration transmission system.

Vehicle information: the driving distance of E70 engine N55 is 164 1 10KM. Fault phenomenon: the owner reports that the vehicle is speeding up, the transmission system is faulty, and the fault indicator light is on. Repair process: 1. The fault code detected by ISTA special computer is 2C57, booster pressure adjustment, reliability: low pressure. Perform the steps in "abl _ dit _ b1214 _ TVD _ 46 _ LDR-Boost Pressure Regulator" and test according to the steps. The exhaust baffle is working normally. Under the control of the automobile computer, the vacuum valve rod of the turbocharger wastegate works normally. Even if the cycle starts, air pressure reducing valve can hear the movement sound. No leakage was found when the air intake system was sealed with the fog tester. No abnormality was found in the three-way catalytic detection. The exhaust gas turbocharger is tested, and the results show that there is no fault of low boost pressure. After performing the ABL step, you will be prompted to program in ISTA-P3.58.0 or later. After programming with ISTA-P, the fault still exists in trial operation. 2. Read the fault code again and try again. The results show that the fault occurs in the process of slow acceleration every time, and the fault of transmission system will not affect the acceleration. When the vehicle is tested on the expressway, the sudden acceleration to 200km/H will not cause the fault of low pressurization. 3. Because the fault of this car appears in a specific speed range, there is no diagnosis idea for the time being, so simply consider eliminating the fault of low pressurization. In addition to the above factors, there are vacuum degree of vacuum hose, crankcase pressure, pre-throttle pressure sensor/post-throttle pressure sensor, EPDW valve, DME and turbocharger. 5. After replacing the front accelerator booster sensor and the rear accelerator booster sensor of the same vehicle, the test run failure remains unchanged. According to the comprehensive diagnosis, it is decided to replace the turbocharger for testing. Confirm that the valves of turbine, pump wheel and wastegate of turbocharger are normal. When checking the valve of circulating air pressure reducing valve, you can see that the diaphragm of the valve is broken into small holes. According to the structure of turbocharger, please thoroughly understand why the fault of too low boost pressure only occurs at a specific speed. 6. Because the turbine speed changes rapidly during the rapid acceleration, the boost loss does not affect the intake boost at this time, so the boost of the car is low when it is slowly accelerated to about 2000r/m, and there is no abnormality during the rapid acceleration. After replacing the circulating air pressure reducing valve, the test run fault was completely solved. Maintenance summary: 1. During normal pressurization, pressurized air enters the diaphragm through four small holes. At this time, the pressure in the diaphragm acts on the inner side of the valve, and the elasticity of the spring is greater than the pressurization pressure on the outer side of the valve, so that the valve cuts off the bypass valve. 2. After the circulating air pressure reducing valve power supply is turned off, the valve is pushed out under the force of the spring inside the diaphragm, and the valve performs the closing process of the bypass valve. When accelerating slowly, the boost pressure enters the diaphragm through four small holes at the top of the circulating air pressure reducing valve valve, and the diaphragm is less damaged, so it becomes a lost data stream of boost pressure. 3. When verifying the fault, we must find out the conditions and laws of the fault. The lack of theoretical knowledge ruled out circular air pressure reducing valve from the beginning and took many detours.