<p>This study examined the residual stress in automotive engine crankshafts, crucial to converting reciprocating motion into rotational motion. Two crankshafts were analyzed: one used and one unused. Samples from the crank pins of the new crankshaft were thermally treated to eliminate residual stress, while wire-cut samples from the used crankshaft retained inherent residual stress. The stress states of both sets of samples were compared using Barkhausen noise amplitude measurements from the fillet regions of the crank pins, which were subjected to high load and stress. X-ray diffraction was also used to validate the Barkhausen noise results. The findings revealed considerable differences in the stress states between the used and new crankshafts, indicating the impact of usage on the mechanical behavior of the crankshaft. This study provides a novel method for quantitatively assessing the durability and performance of automotive components.</p>