Thermoelectric generators (TEGs) have become a promising technology for vehicle exhaust heat recovery. Many models and prototypes have been developed and validated with very promising results. The majority of them have been tested under steady-state engine conditions. However, light-duty vehicles operate under wide variable loads, causing significant variation of TEG performance. The purpose of this study is to test and analyze an automotive thermoelectric generator (ATEG) under different steady-state engine conditions and under the transient New European Driving Cycle (NEDC). Results show that both thermal inertia and pressure drop play a key role in designing an ATEG for real applications. Variations on exhaust temperature and mass flow rate prevent achievement of thermal steady state. Consequently, total energy generated during the NEDC is lower than that expected from a steady-state analysis. On the other hand, excessive pressure loss on the exhaust considerably minimizes engine performance. Results show that the overall power generation of the ATEG can be significantly improved by maximizing the heat transfer through TEMs using a finned geometry, employing lower temperature thermoelectric materials and including a hot-side temperature control.