This study investigated male post-mortem human subject (PMHS) responses and injuries using an unreinforced production seat in rear-facing frontal impacts. Two PMHS were tested at ∆V of 56kph in an unreinforced production seat with a pretensioner in upright and reclined seatback angles. PMHS were positioned using the same procedures as in a previous study. An instrumented panel was installed behind the seatback with a gap of 100mm that limited seatback rotation. PMHS instrumentation was identical to those used in the previous study with additional strain rosettes on the ribs and strain gauges on the superior pubic rami of the pelves. The major PMHS injuries occurred in the thorax and spine. Both PMHS sustained critical rib fractures (AIS5) and serious to maximal cervical spine injuries (AIS3-6). All rib fractures occurred before maximum seatback rotation. Posterior rib principal strain directions were in an upward direction, indicating shear in the thorax. Both PMHS sustained cervical and thoracic spine injuries due to excessive ramping-up motion. No pelvis fractures occurred, but fibula fractures were observed which suggests more energy was transferred to the lower extremity than in previous tests. The results from this study can be utilised for designing rear-facing seats in vehicles with automated driving systems.