The mileage is about 40 thousand km, and the model is TRJ150L, which is equipped with 2TR engine in 2012, FAW TOYOTA Prado sport utility vehicle. User response: after parking for one night, the engine will be turned off quickly after second days of startup, and it needs to start again. Inspection and analysis: the maintenance personnel test the engine control unit, found the fault code B279A---- anti-theft control unit communication line signal continuous high output, the fault code can be cleared. The vehicle anti-theft control unit and the engine control unit transmit data through the data bus. If the communication is interrupted, the engine is not allowed to start. According to the situation reflected by users, the fault should belong to the anti-theft effect. Refer to the circuit diagram of the maintenance manual, measure the communication line between the anti-theft control unit and the engine control unit, and turn it into normal. Measuring the security line of the anti-theft control unit, it is found that the resistance between the body and the body is 235 ohms, which is abnormal. The poor contact of the anti-theft control unit by the iron wire will inevitably lead to the voltage error of the data bus signal. Measure the resistance between the anti theft control unit and the G44-12 terminal, which is 0.7 ohms. The problem lies in the connection between G44-12 and the body. Referring to the circuit diagram, it is found that the G44-12 must be connected to the body through the 3A-71 terminal of the junction box unit J/B NO.3. Remove J/B NO.3 and check the internal conduction of J/B NO.3 in comparison with the circuit diagram. It is found that 3A-71, 3C-44, 3B-20, 3A-34 and 3C-5 in JIB NO.3 have traces of influent corrosion, and the problem lies here. Troubleshooting: thoroughly clean J/B NO.3 with circuit cleaner, test the vehicle on the second day after parking for one night, and the engine start process is completely normal.