The Allison T14/A50 Transmission Control Module (TCM) is a common component in 2009-2015 Chevrolet and GMC trucks with the 6.6L Duramax engine. These TCMs are known to fail, often due to internal circuit board issues, leading to various transmission problems. A failed TCM can result in messages like "Range Shift Inhibited," "Service Brake System," or "Service Stabilatrak". Other symptoms include erratic shifting, loss of the gear shift indicator, and the transmission slamming into drive or reverse. A failing or failed TCM can also cause a Check Engine Light to illuminate.