U0121 GMC - Lost Communication With Electronic Brake Control Module

Repair Importance Level: 3/3
Repair Difficulty Level: 3/3   
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Possible causes

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

Tech notes

There is a factory service bulletin for the following GMC models:

2007-2010 GMC Sierra
2007-2010 GMC Yukon Models
2008-2010 GMC Sierra Hybrid
2008-2010 GMC Yukon Hybrid

GMC Factory Service Bulletin OBDII Code U0121

Possible symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)

U0121 Gmc 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.
OBDII Code U0121 Gmc - Lost Communication With Electronic Brake Control Module - AutoCodes.com

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U0121 GMC Comments

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