Code U0121
 

Very strange, I haven’t had a problem and haven’t done any work in almost 1k miles. My 8 has just over 144k miles with a freshly remanned engine that I installed myself and this code came on randomly while driving. All of the gauges including the rpms dropped and went back to normal but now my cel and came on which was very weird. Any help is appreciated!

Loose battery cable perhaps? The code is loss of communication with the ABS module, but since your gauges dropped I'm thinking momentary loss of current.

You were correct! It was just a little loss of current in which I just reset the ECU and everything and the light hasn't come back ever since.