On certain vehicles, the sensing and diagnostic module (SDM), which controls airbag and pretensioner deployment, contains a software defect which may prevent the deployment of frontal airbags and pretensioners in certain circumstances. Failure of frontal airbags and seatbelt pretensioners to deploy in a crash (when warranted) could increase the risk of injury. Correction: Dealers will reflash the SDM with new software. In vehicles with any previous deployment events recorded in the SDM, the dealers will replace the existing SDM with a new SDM containing the latest software. Note: This recall affects 2014-2017 model year Sierra LD/Silverado LD models and 2015-2016 model year Sierra HD/Silverado HD model vehicles.