In the Brazilian automotive market, the Flex Fuel vehicles are known for their ability to run with gasoline, ethanol, or any proportional mixture of them. To allow this flexibility, the vehicle’s fuel system has been adapted to support differences in fuel types available in the Brazilian market, including contaminated fuel that in this paper will be treated as aggressive ethanol. The fuel pump, which has the function of supply fuel to the engine, had to be specially developed for the flex fuel application to support the specific characteristics in Brazilian ethanol. The focus of this paper is to evaluate the influence of different fuels - gasoline, ethanol, and aggressive ethanol in the sparking level of the DC fuel pump commutation system. Using a digital oscilloscope, the voltage signals of the fuel pump were recorded, and it was applied a mathematical formulation to determine the sparking level of the DC motor for the different fuels. The results show that the higher the voltage, the larger the spark level intensity in all fuels considered herein. In addition, the increase in the fuel conductivity also showed an increase on the value for the evaluated parameter. Consequently, the fuel electrical conductivity that is one of the parameters monitored by the Brazilian specification, has a critical influence on the fuel pump operation, which can affect the fuel pump lifetime, due to electro erosion wear caused on the carbon brush and carbon commutator owing to the sparking level.