U0121 Code: Meaning, Causes, and Symptoms | OBD2 Codes

U0121 – Lost Communication With Electronic Brake Control Module


U0121 Possible Symptoms


Engine Light ON (or Service Engine Soon Warning Light)


U0121 Possible Causes


Faulty Electronic Brake Control Module (EBCM),EBCM harness is open or shorted,EBCM circuit poor electrical connection


U0121 Description


Modules connected to the high speed General Motor Local Area Network (GMLAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.