If you use ardupilot firmware 4.0 or higher, you may encounter this problem.
This is due to insufficient external power supply. The firmware above 4.0 needs to use the 3DR power module, and the output voltage of the 3DR power module must be 5.2V to 5.8V, and cannot be lower than 5.2V, otherwise an error will be reported.
How to sove it?
1.Use 3DR Power Module to power for Pixhawk,make sure the output voltage of the 3DR power module must be 5.2V to 5.8V, and cannot be lower than 5.2V, otherwise an error will be reported. Do not use the 5V BEC, It is not enough to provide enough voltage.
2.IF you do not have 3DR Power Module ,or the 3DR power Module is Less than 5.2V. You can upload the stable version 3.4.6, download the 3.4.6 from here , http://firmware.ardupilot.org/Copter/stable-3.4.6/PX4-quad/ArduCopter-v2.px4 It is recommended to use the stable version 3.4.6, which is the most stable verified.
3.Do not select Board Voltage at Arm_check parameter,then remember to click the “Write Params”Button.