Two possibilities:
1. Motor failure or working outside of spec
2. Electronic Speed Controller circuit damage
And if you mean what causes it to appear on your phone:
1. ESC circuit contains micro-controller which gathers information about motor rotation speed, voltage and current. It also monitors whether a change to input causes a proper change in motor movement. If any of the values exceed bounds for certain conditions, the ESC circuit sets proper error bit in its state value.
2. The ESC micro-controller is connected to Flight Controller via serial interface. The FC sends ESCs configuration requests, and receives back the status value (motor speed is set by a different interface, because it requires fast rections).
3. If any of the error bits in status value is non-zero, the FC marks that ESC as faulty. It later sends information about faulty ESCs to Radio Controller through the transmitter on OFDM board.
The annoying thing about it is - the FC doesn't share the information about what specific error the ESC reported. It only shares whether there's a fault or not. Fortunately the details about ESC error can be retrieved from the DAT logs.
Go over to DJI Forum and ask Moderators for FW 1.11.30 ..... a 'fix-it' for ESC errors for some P3A / P3P after recent 1.11.20 FW updates...
If you are not using 1.11.20 FW - then it probably does not apply ... but maybe worth asking them.
What I do not understand is why DJI insist on making people ask for this 1.11.30 FW instead of having online with just a comment ... for ESC error situations ... but NO - you have to go ask them.
