BMW 730Li engine starting difficulties
  • Automotive

A 2003 730Li BMW E66 with a mileage of about 120 thousand km. Users reflect: it is difficult to start the car every morning, the starter is not working, and the day after the start is normal, but the same problem will appear on the second morning. Fault analysis: the fault is obviously caused by battery loss. The self diagnosis is made by using the diagnostic instrument. Multiple control modules store fault codes which are related to low voltage. Combined with the characteristics of the fault analysis: after starting a day after starting, the possibility of generator and battery failure can be eliminated basically, the most probable cause of the fault is the dormant current or the normal dormancy of the vehicle. Close the vehicle and observe the dormancy current with the diagnostic apparatus. After about 30min, the dormant current is still 4.68A, which is too large and should be in the 80mA range. Observe the inside of the car and find that the lighting indicator of the remote control key hole and the start / stop button is still lit. It shows that the vehicle bus has been in a state of operation. Under normal conditions, the lighting indicator of the key hole and starting / stopping button after the locking of the vehicle is automatically extinguished within 3 min, and the seat appliance and switch indicator is extinguished within 5 ~ 16min, and the whole car begins to enter the dormancy state. Combined with past experience, the suspect control module is disconnected one by one, and then observe the remote control key hole and the start / stop button lighting indicator. It was found that when the right front door control module was opened, the indicator was extinguished in 3 min, and the dormancy current of the diagnostic instrument was 1. 2A, which indicated that the cause of the fault was the damage of the right front door control module. The replacement treatment is carried out, and the failure is completely eliminated. The right front door control module is shown in Figure 5-34. The diagnosis of dormancy current is an important part of troubleshooting for starting trouble and battery failure. There are dozens of control modules in the limousine. If one of them fails to work properly, it may cause excessive discharge of batteries. Generally speaking, the vehicle entering dormancy is divided into the following stages: the bus end 15 closes, the bus end R closes, the vehicle insurance lock dies, the bus begins to dormant, the electric appliance is closed after 8 min, and the bus end 30B is closed. When a vehicle is equipped with a telephone and a parking heating system, 60min is required to enter the dormancy process. 30min is needed without these devices.