File in Section:

Service Bulletin

Bulletin No.:
Date:

PIT4056H
October, 2015

PRELIMINARY INFORMATION
Subject:

Unable To Communicate With The EBCM DTC U0121

Models:

2008 - 2015 Buick Enclave
2007 - 2014 Cadillac Escalade, Escalade ESV, Escalade EXT
2007 - 2013 Chevrolet Avalanche, Silverado 1500
2007 - 2014 Chevrolet Suburban, Tahoe
2010 - 2015 Chevrolet Camaro
2009 - 2015 Chevrolet Traverse
2007 - 2015 GMC Acadia
2007 - 2013 GMC Sierra 1500
2007 - 2014 GMC Yukon, Yukon XL, Yukon Denali, Yukon Denali XL
2008 - 2009 Pontiac G8
2007 - 2010 Saturn Outlook
This PI was superseded to update Recommendation and Model Years.
Please discard all copies of PIT4056G.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern
Some owners may comment that the ABS and red brake lamp is on in the IPC. When trying to retrieve DTCs, the
scan tool will not communicate with the EBCM. The scan tool will communicate with all other high and low speed GM
LAN modules and some may have set a U0121 DTC against the EBCM. While performing normal diagnostics it will
be found that the power circuits, ground circuits, communication enable signal circuit, and the GM LAN circuits going
to the EBCM test good. This testing may lead to replacement of the EBCM; however, the concern may still be
present after installing the new EBCM.

Recommendation/Instructions
This concern may be caused by one of the following issues:
1. (If Equipped with StabiliTrak RPO JL4) The Yaw and Lateral Accelerometer (Multi-Axis) Sensor or the Steering
Wheel Angle Sensor supply voltage (circuit 2087 Dk Green) shorted and pulling down the internal circuitry of the
EBCM. Not all vehicles use circuit 2087 to supply voltage to the Steering Wheel Angle Sensor, so be sure to
check Service Information for the specific vehicle that is being serviced. If circuit 2087 is backed out of the
EBCM connector and communication returns, inspect for either this circuit being shorted to ground or for a
sensor concern. On some full size utility vehicles, the circuit may be shorted under the passenger front seat at
the rear camera module bracket. Repair the circuit as necessary and reroute to prevent the concern from
reoccurring
2. A shorted WSS or WSS wiring. In many cases, this is found on Full Size Trucks and Utilities that have
aftermarket lift kits, wheel bearings, and/or WSS wiring. Inspect the WSS sensor wiring for any broken/shorted/
chaffed circuits. If none are found, unplug the WSS one at a time and see if communication returns. If so, repair
and/or replace any wiring/connector and/or WSS issues.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is
resolved without completing every step, the remaining steps do not need to be performed.