Since the early years of the trade, car mechanics linked their craft skills to the clinical expertise of medical physicians. They claimed to use such methods as differential diagnosis or to employ their ears to listen for technical flaws: “If the physician cannot make his diagnosis by the appearance of the patient, he will take his stethoscope and listen to the patient’s body. This is how you ought to proceed with your car engine as well.” In this popular image “auto-doctors” shared a symbolic and practical tool with medical physicians: the stethoscope. However, this was not a one-sided comparison, as car mechanics’ listening practices were equally acknowledged by physicians. In one 1960s medical handbook dedicated to the practice and technique of auscultation, a sound-comparing stethoscope, the symballophone, is introduced through reference to similar instruments used by car mechanics to locate missing cylinders. Mediate auscultation, or diagnosis using a stethoscope, initially marked an important shift in the construction of medical knowledge and the definition of professional expertise. However with the advent of more visual and measurable forms of diagnosis in the 1950s and 1960s, auscultation’s real potential is more and more frequently put into question or neglected because it is deemed a subjective, expert, individualized practice. Roughly at the same time, similar shifts from sonic to visual means of diagnosis occurred in the car mechanics trade. The practice of diagnostic listening became contested by new instruments like the oscilloscope or the lung X-ray which were depicted as more objective and reliable than the expert ear. Our presentation will explore these connections, investigating the sonic practices of the two very different fields of medical auscultation and car mechanics. We will reveal how and when listening was considered a legitimate tool for knowledge acquisition. The focus lies in explaining the bodily technique of diagnostic listening: the mode of listening physicians and mechanics employ to detect and identify bodily pathologies and technical malfunctions. Through close readings of trade journals and medical textbooks appearing in the first postwar period (1950-1970), we will compare descriptions of the types of skills developed in these parallel forms of auscultation. Furthermore, we will reflect on the epistemic status of the knowledge which physicians and mechanics generated through these sonic practices.