Arrangement for determining the lambda value of an air/fuel mixture

An arrangement determines a voltage which indicates the lambda value of an air/fuel mixture supplied to a combustion engine generating exhaust gas during the operation thereof. The arrangement includes a two-cell oxygen probe mounted in the exhaust gas flow of the engine. The two-cell oxygen probe has an exhaust-gas space for the exhaust gas and an ambient-air space for ambient air. The oxygen probe has a pump cell having two electrodes and a sensing cell having two electrodes. A switchover stage outputs a voltage indicating the electric pump current through the pump cell when a control to the lambda value deviating from one is to be made and outputs that Nernst voltage which is taken off between the electrodes of the sensing cell facing into the ambient air and one of the remaining ones of the electrodes when a control to the lambda value one is to be made. For controlling to the lambda value one, the Nernst voltage supplies a significantly more precise signal than the voltage derived from the pump current.