The ECU can tell if the AMM is faulty due to a wiring fault or other (not all) reasons, now you have run the engine with the AMM disconnected you will have a fault code stored to say you have an AMM open/short circuit and so you now have no idea if it was there before or not, you should always read the codes before carrying out any tests. Just because the AMM being disconnected does not make any difference to the way it runs does not mean the AMM is not faulty, that is an old wives tinterweb tale.