System for measuring the impedance of an ion exchange membrane in a fuel cell stack including N electrochemical cells separated by bipolar plates, where N is a natural integer, the system comprising: - a current generator allowing a current to be applied to the fuel cell stack; - a device for measuring voltages of the cells; and - means for determining the impedance of the membrane according to a voltage ripple measured by the measurement device across the terminals of the measured cells when a current is applied by the current generator, these means being installed in the device for measuring voltages of the cells, the system being characterised in that: the device for measuring voltages of the cells comprises: - at least two voltage measurement modules (19a, 19b, 19c, 19d), each module being capable of measuring M voltages across a set of contiguous cells of the fuel cell stack, where M is a natural integer smaller than or equal to N/2, the group of cells measured by the first module being adjacent to the group of cells measured by the second module; - an electronic computer; and - a wired communication bus connecting the at least two measurement modules in series to the computer, each of the measurement modules comprising: - mechanical means for fastening the module to the fuel cell stack, - electronic means for measuring voltage; - electrical means for connecting the bipolar plates to at least one electronic means for measuring voltage; - means for connecting the electronic means for measuring voltage to the communication bus and - the electrical connection means include terminals that can also be used as mechanical fastening means. - a current generator allowing a current to be applied to the fuel cell stack; - a device for measuring voltages of the cells; and - means for determining the impedance of the membrane according to a voltage ripple measured by the measurement device across the terminals of the measured cells when a current is applied by the current generator, these means being installed in the device for measuring voltages of the cells, the system being characterised in that: the device for measuring voltages of the cells comprises: - at least two voltage measurement modules (19a, 19b, 19c, 19d), each module being capable of measuring M voltages across a set of contiguous cells of the fuel cell stack, where M is a natural integer smaller than or equal to N/2, the group of cells measured by the first module being adjacent to the group of cells measured by the second module; - an electronic computer; and - a wired communication bus connecting the at least two measurement modules in series to the computer, each of the measurement modules comprising: - mechanical means for fastening the module to the fuel cell stack, - electronic means for measuring voltage; - electrical means for connecting the bipolar plates to at least one electronic means for measuring voltage; - means for connecting the electronic means for measuring voltage to the communication bus and - the electrical connection means include terminals that can also be used as mechanical fastening means. the device for measuring voltages of the cells comprises: - at least two voltage measurement modules (19a, 19b, 19c, 19d), each module being capable of measuring M voltages across a set of contiguous cells of the fuel cell stack, where M is a natural integer smaller than or equal to N/2, the group of cells measured by the first module being adjacent to the group of cells measured by the second module; - an electronic computer; and - a wired communication bus connecting the at least two measurement modules in series to the computer, - at least two voltage measurement modules (19a, 19b, 19c, 19d), each module being capable of measuring M voltages across a set of contiguous cells of the fuel cell stack, where M is a natural integer smaller than or equal to N/2, the group of cells measured by the first module being adjacent to the group of cells measured by the second module; - an electronic computer; and - a wired communication bus connecting the at least two measurement modules in series to the computer, each of the measurement modules comprising: - mechanical means for fastening the module to the fuel cell stack, - electronic means for measuring voltage; - electrical means for connecting the bipolar plates to at least one electronic means for measuring voltage; - means for connecting the electronic means for measuring voltage to the communication bus and - the electrical connection means include terminals that can also be used as mechanical fastening means. - mechanical means for fastening the module to the fuel cell stack, - electronic means for measuring voltage; - electrical means for connecting the bipolar plates to at least one electronic means for measuring voltage; - means for connecting the electronic means for measuring voltage to the communication bus and - the electrical connection means include terminals that can also be used as mechanical fastening means.