A method for defect detection for a signal line between an electrode and a measuring- and/or evaluation unit of a magneto-inductive flow measuring device having at least one measuring- and/or evaluation unit, as well as a measuring tube with at least two measuring electrodes and a third electrode, comprising steps as follows: A) ascertaining a ratio of at least two measured electrical impedances between the measuring electrodes and/or between at least one of the two measuring electrodes and the third electrode; B) comparing the impedance ratio with a desired value range and C) outputting a defect report, when the impedance ratio exceeds or subceeds the desired value range, and a magneto-inductive flow measuring device.