A magnetic flowmeter (20) for measuring flow of a process fluid in a pipe (22) includes a magnetic coil (26) disposed adjacent to the pipe (22) configured to apply a magnetic field to the process fluid. First and second electrodes (30, 32) are disposed within the pipe (22) and electrically coupled to the process fluid and configured to sense an electromotive force (EMF) induced in the process fluid due to the applied magnetic field and flow of the process fluid. Input circuitry (148, 150) is coupled to the first and second electrodes (30, 32) and provides an output related to the sensed EMF. Diagnostic circuitry (212) coupled to the input circuitry (148, 150) is configured to identify a saturation related condition and responsively provide a diagnostic output (204). In another embodiment, saturation prevention circuitry prevents saturation of the input circuitry.