the K line on the oBD connects to all the controllers, so whilst you might be able to read the other controllers it doesn't mean the ECU will read, it's no different to removing the ecu and scanning the car. Only way to check is to remove the ecu and read it on the bench, ie directly. It may be an on board fuse/earth has popped and the ecu is dead or in some cases reflashing the ecu in bootmode will fix the issue.
If you want to send me the ecu I can take a look and see if it can be read on the bench/ reflashed. Drop me a pm.