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Vehicle is at the dealership, and the mechanic says the TCM is needed, but no codes are displayed because the TCM is not at all communicating. The car won't change into any gear anymore. Allison 6 speed 2013 GMC 3500 HD Denali. Just urgently need your thoughts.
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Posted : 10/05/2023 6:50 pm
Thank you for reaching out. Not having codes will make it difficult to isolate the problem. If the dealership confirmed no communication then the issue could very well be the TCM however all other components need to be thoroughly inspected. Basically, the software is no good. We'll have to replace all microprocessors and install GM-approved software to fix the issue.
This post was modified 7 months ago by Serge - UpFix Team
Posted : 10/05/2023 6:50 pm