In 2012, Land Rover found a 4 sport utility vehicle with a mileage of about 60 thousand km. User reflection: the car can't drive normally. Inspection and analysis: the maintenance personnel commissioning test found that the automatic transmission of the vehicle has entered the protection mode, and the gear is locked in the 3 gear. Detection of transmission control unit, found fault code P0658---- electronic actuator power supply voltage is too low; P2716---- oil pressure regulating solenoid valve D failure. After reading the data flow of the transmission control unit, it is found that the supply voltage is 13.40V, but the power supply voltage of the execution element is 10.40V. Check the circuit diagram. Turn on the ignition switch and measure the voltage of the power supply terminal of the transmission control unit. The voltage of the power unit C0193A-14 of the control unit is 12.65V, and the voltage of the C0193A-9 of the power supply end of the executive element is 12.60 normal. After starting the engine, the above 2 voltages change to 13.40V, but the supply voltage of the actuator in the transmission control unit still shows 10.40V. Because the voltage of the C0193A-9 terminal is normal, it can only be a bad contact between the wire and the body of the executive element. The inspection found that the fixed bolts of the C0560L 1 of the operative element were loosened, and the problem is here. Troubleshooting: tighten the fastening bolts of the tie up and confirm the trouble shooting.