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Buick Has Failure to Communicate

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This bulletin applies to all 2013-2018 Buick and other GM models. When diagnosing multiple DTCs, one of which includes U****Byte 71, any control module may set a DTC for one of its inputs, and that data is shared across the communication bus for other modules to do their respective functions. 

The receiving module may set a 71 byte type DTC. In these cases, the DTC list should be examined for what control module or missing data the U codes point to and check for DTCs related to the managing control modules’ inputs. 

As a general rule, never replace components for “Invalid Data Received” codes within the component. Resolve the system-wide non-communication (not U codes) first and re-evaluate.

Below is one example in which an intermittent wheel speed sensor code was setting U codes across buses and the root cause was tracked back to the wheel speed sensor and EBCM messages:

Problem # 1: The DIC shows “Service Stabilitrack” and “Service ABS.”

Condition: When the EBCM sets any of the wheel speed sensor codes C0035-C0050, it yields “Service Transmission”, “Steering Assist Reduced” and “AWD off” in addition to “Service Stabilitrack” and “Service ABS” messages. This is in addition to several U codes corresponding to the above messages which may include U0121, U0131, B1011, U0414, C0040, U0422, U0415, U2502, U0401, U0403 and U0402.

Cause: The EBCM would set the wheel speed sensor code intermittently, triggering a system malfunction message to be transmitted, resulting in multiple  U codes across the chassis expansion and HS CAN buses. The multiple U codes can cause mis-diagnosis. An erratic wheel speed signal can cause this failure due to the miscommunication in the system when it intermittently fails. When you review the ABS data you may find an erratic signal from the wheel speed sensor. This can be caused by a faulty front hub wheel bearing.

Correction: Diagnose the wheel speed sensor following the service manual. In this example, it was diagnosed that a faulty front hub bearing was the cause of the erratic wheel speed sensor signal.

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