By simulating the experimental properties of a potentiometric CO2 sensor based on Na-alumina, it is confirmed that the conclusion previously drawn about the role of the electron conduction in such a sensor is qualitatively correct. Quantitatively, however, the literature data on the p-electron conductivity prove to give rise to an incorrect picture about the impact of the electronic transference on the sensor performance. The p-conduction parameter a+ determined from a critical evaluation of the sensing characteristics reveals to significantly differ from the literature data with respect to both the magnitude and the temperature dependence. It lies close to the sodium potential of the measuring electrode and, moreover, depends on the CO2 pressure in the surrounding of the electrolyte. As a result, a+ must be considered a variable rather than only a temperature-dependent constant.