The Buick lacrosse 2. 4L car with a mileage of about 143 thousand km in 2007. Customer response: the interior lights on the roof of the car are always bright. Inspection and analysis: the car interior lamp setting is controlled by the opening or closing of the door. The body control unit (BCM) receives the signal on the door lock switch on the door, the door of the lock door switch provides the signal in the open state to light the inner lamp (door control lamp), cut off the delay power supply of the RAP accessories, start the anti-theft system and delay the lock door and so on. If the lock door switch provides the wrong signal, it may cause the interior lamp to be always bright. Before troubleshooting, we will briefly analyze the working process of the lock switch of lacrosse car. In the door lock motor assembly. The door lock motor and lock switch are integrated. Figure 1 shows the circuit diagram of the lock switch, which indicates that the door lock is completely closed. The lock door switch is a switch with 3 positions, which are closed, half closed (not closed) and open (gated). In practical use, the closing of the door switch means that the door is completely closed to the second lock, and the half closure of the lock switch means that the door is only closed to the first lock, and the unclosed signal is mainly used for the "door of the car". The body control unit (BCM) provides voltage for the lock switch, and the lock door switch provides the 3 state signals of the door to BCM. As an example of the left front door switch, it can be seen from the circuit diagram that when the left front door lock always connects to the gate of the 7 foot (low potential signal), the body control unit (BCM) thinks the door is in the open position, and the line will be switched on only when the left front door is open. When the No. 6 leg is connected with a tight line (low potential signal), the body control unit (BCM) considers the door half closed. According to the circuit diagram, when the door is in the open and half closed state, the line connected with the No. 8 foot will be locked by the lock switch. When the BCM did not receive the low potential signal on the two lines of the gated and not closed, the door was considered to be in full clearance. So how do we check the signal status of the lock switch? We can read the "close / open" state by reading the "XX door open switch" signal in the BCM data stream by TECH2. Therefore, most of the vehicles that appear to be on the inside light or the alarm system can alarm without any reason can use TECH2 to find out the wrong door locks accurately. Troubleshooting: using TECH2 to read the data flow, you can see that whether the right rear door is open or closed, the data flow is always displayed in the open state. After replacing the motor assembly of the right rear door lock, the car interior lights are always bright.