How to fix U0121 Code: Lost Communication with Anti-Lock Braking System (ABS) ModuleA U0121 means that the vehicle CAN Bus can’t communicate with the Anti-Lock Braking System (ABS) Module.The CAN (Controller Area Network) is a protocol that allows the ECM, PCM, TCM, and ABS modules to communicate with each other.Symptoms of a U0121 Code: Warning lights (ABS ESP BAS Lights)ABS performance issuesPossible Causes of a U0121 Code: Blown FuseIssues with Alternator Charging or Battery Faulty ABS contro