a 2009 models Ford Focus 1.8 L sedan, equipped with automatic transmission, mileage 22000 km, users complained that the car door can not be two back door latch, rear right door power window switch can not lift a glass, driver’s side of the centralized control switch does not control the right rear door power window.
After receiving the vehicle, as determined by the user of the fault test. Combined with the author’s experience in the maintenance of the car according to the fault symptoms, possible causes for the car: the control unit hardware conflict, line failure or malfunction control unit itself. First of all, taking into account the weather suddenly changes or the improper operation of the driver control unit unstable, resulting in network communication error, can not recover on their own, the control unit stops working. For this reason, we decided to conduct a battery power down. After the negative battery cable off of 10 min, which was refitted, test all normal. Successive trials locking and unlocking functions and movements were normal window, but the operation several times, the fault occurs again, power window switch indicator is off.
Figure 1
2
At the 2009 model year Ford Focus sedan, 4 between the door control unit is connected using CAN-LIN driver door control unit and the front passenger-side door between the control unit uses MS-CAN connections, and the control unit driving the rear left side door between the door control unit using LIN wire connection, front passenger-side door control unit and the right rear door control unit using LIN between the line connection (FIG. 1). The driver side door of the diversity control switch controls the right rear door locks and the process window lifter is: the driver door control unit MS-CANrarr; front passenger door control unit LINrarr; rear right door control unit rarr; or rear right door motor window regulator motor. The author then open the right rear door linings, door control unit after checking the right connector, connector intact, completely normal connection. The line will not be the problem? Then check the relevant line (FIG. 2). Using CAN-LIN line connection between the vehicle control unit 4, for measuring the author right front control cable connected to the communication unit between the control unit to the right rear door. It was measured, no grounding line section and the short circuit. Since the door control unit and the front passenger side door rear rightBetween the control unit is passed by the LIN signal line, it will be front passenger door control unit is damaged it? Since the transmission line between the LIN is a digital signal, it decided to observe the signal waveform by means of a transmission line LIN VMM oscilloscope. Since normally the left door control unit, as a reference, the author observed a waveform of the first left door control unit a transmission signal (FIG. 3) with an oscilloscope. Thereafter, the author has an oscilloscope waveform of the signal LIN right door control unit observed. After careful observation comparison, the signal waveform and the signal waveform on the right side of the left side is completely different. Since the left door control unit and a normal line, it may determine the right door control unit problematic. After analysis, the author determines the front passenger-side door control unit is damaged.
Figure 3
After the replacement of the control means, testing the fault persists. Again observed with an oscilloscope waveform of the right line signal LIN, they found no change in the signal waveform as the control unit. Is control program of the control unit in question? So I turn to the control unit new for the re-match, but the test failure remains. At this point the situation so I was somewhat puzzled, the line is no problem, the control unit can also be replaced, why not fault any change it? I decided to consult the user about the specific circumstances at the time of failure, hoping to find some clues.
Figure 4
in consultation with the user to know the car was recently visited by a crash, hit the front passenger side door, and then they sent repair shop for repair, vehicle repair, using just discovered this problem. It seems to be related to the failure of the car collision. As the car’s collision repair work is not in my station, so I follow the user find the relevant personnel to repair the accident, and they understand the situation. Upon inquiry sheet metal technician that the car due to the collision, resulting in the front passenger-side power window lifter damage, and since the window regulator motor, the control unit one, then replaced together. Is it wrong to change the control unit? To determine the author’s judgment is correct, and sheet metal technicians found the old door control unit together. And after the vehicle door control unit can change the comparison, part number two is not the same as the control unit (FIG. 4, FIG. 5), it seems that the problem really vehicleDoor control unit.
Figure 5
back to the station to find the original car same door control unit and after replacing, by matching test vehicle function control unit restore normal troubleshooting.
Summary: As the sheet metal electrical and mechanical maintenance technician understand, resulting in the wrong car door control unit installed, no further door control unit match. By the maintenance of the car, also suggest that the majority of peers, be sure to follow the strict maintenance procedures during vehicle maintenance. If the vehicle is carefully scrutinized in the maintenance inspection, the car will not believe the factory, car problems naturally, will not be delivered to the user. In addition, the maintenance of the car, also suggest that the majority of maintenance personnel, be sure to find the part number of the old parts with new parts when replacement parts are compared. If different, to find out whether there is a real alternative to the relationship, and then replace operation. Modern vehicle control systems become more advanced, does not own control program in some of the new control unit, it needs to match the work program after loading, the control unit will not replace the work is complete.
(Qian Shan Zhen, Guo Qifeng)