Summary of The post-investigation of DQ400 TCU failures in a production line provides a profound overview of the core causes affecting the product reliability and process steadiness. Since the various repeating defects were identified after Lean Heat Test and the End-of-Line procedure, the Min KL30 current-based failure was treated as the most frequent and dangerous failure. This defectiveness was highly reoccurring, providing significant danger for electrical functions and final customer satisfaction. As a result, a profound RCA and Structured CAPA were conducted. The root cause of Min KL30 failure was identified through the comprehensive analysis of defective samples, Process Audits, and cross-sectional imaging. This RCA determined that the Min KL30 defect appears due to contamination and micro-residues related to solder that are placed in the near valve connector and baseplate sections. Solder balls, metallic dust, and flux residues create unintended conductive bridges between them in a harsh thermal environment, as observed during the LHT process. More so, the inaccurate soldering temperature, excessive amount of conveyor speed, and bad post-soldier cleaning performance contribute to leftover solder debris on the PCBA. The lack of proper guidelines in AXI contributed to the fact that the device was unable to discover the micro defects. On these grounds, a set of corrective and preventive measures was developed and proposed to eliminate the root causes. The major improvements include a cleaning brush thickness and density increase to make it more reliable in post-solder efficiency, re-soldering temperature re-optimization to avoid the molten solder instability, and reduction of the conveyor speed to guarantee constant and uniformly distributed wetting and solidification of solder. Additionally, recommending renovating the AXI inspection system to a novel one, furnished with complex and accurate image processing algorithms, and defect recognition based on AI will increase defect sensitivity and accuracy, with items like small metallic particles or the solder balls covered under the component insides can be otherwise imperceptible. The estimated results from enacting these measures are immense. While examining the vital process parameters and replacement of the inspection capability, the overall solder defects rate will be at 80 to 90% reduced levels, directly increasing the First Pass Yield and reducing the numerous leans and reworks. The number of Min KL30 current fires will be reduced, to increase the Mean Time Between Failures, a characteristic of better field reliability, which will boost the test rate reduction, lowering the warranty claim strata. On the production side, the process gauge will have better stability, scarce unanticipated stoppers, and increased Overall Equipment Effectiveness compliance. Economically, these endeavors are seen to result in a Cost of Poor Quality breakdown to a more than tenable limit through more supply of material, enhanced test cycle opportunity, and closely flat resource wastage. Therefore, in the end, this research effectively resolves a significant recurring failure within the production process of the DQ400 TCU. Still, more importantly, it adds to the culture of structured problem solving and data-supported decision-making, which continually strengthens the manufacturing system. The conclusion emphasizes the value of process integration, predictive maintenance, and innovative inspection processes within high-end modern automotive electronic manufacturing. Finally, their successful application consolidates the Production line’s status to successfully address its vision of achieving sustainable quality improvement and associated product reliability and long-term competitiveness standards, as desired by the global automotive industry.