U0101 code what is the fix?

Question

I had a transmission replaced in my mazda 5 sport . ammco told me that that code that came up mean my transmission was bad. so I had them to replaced the transmission so when I went to get it back I drove out the gate and the light pop back on . they said that they test drive it for 10 miles without a problem but I could not get a mile out of it before light pop back on . what is the problem.the code is still saying u0101 lost communciation