I bought my 2010 Mazda 3 without the istop and it had only 1 battery instead of 2. I had the problem with the AT light coming on often and I eventually changed the TCM. The problem still persists! When diagnosing the problem, one of the problems diagnosed is U0101, Lost communication with the TCM. It was there before and after I changed the TCM. What could the problem be?

 

How did you fix it?

 

Not yet sorted. I've changed the TCM and added another battery, before this my car had only one battery. But the problem still continues.