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BMW 740Li car engine can't start
  • Automotive

A mileage of about 80 thousand km, the vehicle is E65, equipped with N62 740Li and automatic transmission of BMW 740Li sedan. Users reflect that the engine can rotate when starting the vehicle, but it can't work, and the dashboard and vehicle display display "brake and driving system failure" fault information. After receiving the car: the initial inspection result is that the battery voltage is too low, causing the starter to run incapable. The battery is charged and then started, the engine can turn, but there is no evidence of initial explosion, indicating that the engine system has no fuel injection or ignition. The connection diagnosis instrument is self diagnosed, and the engine system has two fault codes. The contents are "2774, reliability failure of engine shutdown time, and the fault is present"; "2780, crankshaft speed sensor reference mark error, signal disk tooth shape is incorrect, fault is not stored at present". Fault code 2774 is the nature of the current existence, first diagnose it. Into the function detection menu of the engine system, the diagnostic help information of the diagnostic instrument is that the system time of the power module is not consistent with the system time within the DME module. The reasons for the failure include the poor communication of the CAN bus, the damage of the power supply module, etc. Check the power module and related fuse, no abnormal phenomenon. Remove the fault code, start the vehicle, the fault is still. Connecting the fuel pressure gauge, the fuel pressure is 0kPa during the start-up process. Unplug the wiring harness plug of the fuel pump, connect the test lamp, start up, and test the light, indicating that there is no problem with the line, and the fault is in the fuel pump itself. Replace the fuel pump, start the vehicle and run the engine smoothly. The fault code of the whole vehicle electronic control system is cleared, and the fault is completely eliminated. The bus system of the BMW E65 chassis is more complex, and the control mode of the fuel pump is special. The specific control process is as follows: during the starting process, the engine control module transmits the fuel pump instruction signal to the central gateway module through the PT-CAN bus, and the central gateway module transmits the signal to the SIM mode through the byteflight bus. The block (the main control module of the airbag system), the SIM module continues to transmit the signal to the right B column satellite sensor (SBSR) through the byteflight bus, and the SBSR is then controlled by the fuel pump. This fuel pump control mode improves the safety of vehicles, but the control circuit is more complex and more failures. SBSR has self diagnostic function. If the fuel pump is open or short circuited, then SBSR can store relevant fault codes. The reason for this failure is the excessive wear of the fuel pump, which is a mechanical fault. SBSR can not monitor such failures, so there is no record of trouble codes. Insufficient fuel pressure causes power failure, enabling the system to enable failure protection mode, and displaying information on dashboard and on-board displays. The failure protection mode does not cause the engine to fail to start, but the information needs to be removed after starting.

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