•An automotive thermoelectric generator (ATEG) is built and tested experimentally.•ATEG has been tested under four steady-state points and a WLTC driving cycle.•An electric heater is coupled to an ATEG to warm up the exhaust gases.•The system could reduce up to 97% the pollutant emissions of cold starts. Low exhaust gas temperatures of internal combustion engines, resulting from cold-starts, low loads or low temperature ambient conditions, can compromise the performance of the automotive aftertreatment system. In this situation, the engine is running far from its design point, with a very low performance of the catalytic converter since it has not reached its optimal temperature. This effect can result in more than 20% of the total emissions for nitrogen oxides (NOx), hydrocarbons (HC) and carbon monoxide (CO) during a driving cycle. This study presents a new approach for vehicular thermoelectric generators to reduce NOx, HC and CO emissions and solve the cold-start issue. Authors propose the use of a thermoelectric generator coupled to an exhaust gas heater. This system, that operates autonomously, is designed to transform the waste heat into electric heat that can quickly raise the exhaust gas temperature to the optimal level. Results show that an improvement up to 94% of the mean catalyst’s efficiency can be achieved. In addition, the system could reduce up to 94%, 91%, and 97% the pollutant emissions of NOx, HC and CO, respectively, in a WLTC driving cycle with a threshold exhaust gas temperature of 350 °C.