Thermoelectric generators (TEGs) have been researched and developed for harvesting energy from otherwise wasted heat. For automotive applications this will most likely involve using internal combustion engine exhaust after the catalyst system as the heat source, although applications to exhaust gas recirculation systems and compressed air coolers have been suggested. A thermoelectric generator based on half-Heusler thermoelectric materials was developed, engineered and fabricated, targeting a gasoline passenger sedan application. This generator was installed on a gasoline engine exhaust system in a dynamometer cell, and positioned immediately downstream of the close-coupled three way catalyst. The generator was characterized at over a matrix of steady-state conditions representing the important portions of the engine map, and also at selected transient conditions. Detailed performance results are presented. Measurements indicate the generator can produces over 300 W of power with 900 C exhaust, but less than 50 W when the exhaust is 600 C or below which is typical of the standard test cycles and normal driving.