<p>This study provides a comprehensive investigation into the preload degradation mechanisms of automotive chassis threaded fasteners. These components are subjected to complex and multifaceted vibration environments that significantly influence their mechanical performance. A critical load model is established that incorporates both thread flank plastic deformation and ambient temperature effects, enabling accurate characterization of preload variation under service conditions. By integrating this model with the rotational loosening mechanism, a preload prediction methodology is proposed. The approach is validated through finite element simulations and in-vehicle vibration experiments. Results indicate that the combined influence of frictional slip and progressive plastic deformation at thread interfaces primarily governs preload loss. Moreover, the conversion of measured acceleration loads into equivalent displacement loads facilitates quantitative prediction of preload evolution across the bolt’s service life. The proposed framework not only enhances the reliability assessment of bolted joints but also provides practical guidance for the design and maintenance of automotive fastening systems.</p>