If you unplug the AMM, all the ECU will do is run the car somewhat poorly on what is called "The Limp Home Mode". Sometimes the car will run identically poor with the ECU unplugged, but I could get no clear sympoms of AMM failure on my wife's car with this method. I tested the AMM by installing the spare AMM. The car ran fine, and continues to run fine. We have a spare AMM for each of our three turbo 700 series cars. The ECU is carried in a zip lock bad in the trunk (son's car), or the tool comparment of the wagons. I bought the AMMs when I was not in a hurry and did not pay much for them ($25 each). The AMMs always cost more when you need one right now. Do you know anyone else with a similar Volvo with whom you can do a little parts eschanging for testing?

Always have the engine and key off when unplugging/pluggin in an AMM.