some of the most possibles reasons
1/ The cable is only charge and no data
2/ your USB port is out of date (USB 1.0 , 2.0) when the ECU need more recent one
3/ ECU need cable support higher power and your cable is Weak (eg: ECU need 2.0 amp but cable only support 1.5amp)
4/ your ECU can't be read without specific software
as you can see most of the reason turn around the ECU
PS: As ECU is write in SSD/Flash memory the question of power on/off should not enter for start to read it (opposite as HD powered disk)
my 2.0 advice, i hope it help
