Carbon corrosion represents one of the most critical degradation mechanisms within state-of-the-art polymer electrolyte membrane fuel cells. Its most prominent consequences include the loss of electrochemical active surface area (ECSA), porosity, and electrical contact within the electrode. The present study seeks a detailed understanding of the dependence between the polarization performance losses and the individual loss terms, both as a function of the amount of corroded carbon. A simplified one-dimensional polarization model is developed with the aim to simulatively reconstruct the empirical polarization curve based on in situ cell characteristics during the course of carbon corrosion. It is shown that this model enables the assignment of nearly all voltage losses at various stages of the corrosion process, up to a cell current density of around 2 A cm^–2. Furthermore, the “observer effect” during the carbon corrosion studies is investigated, where it is demonstrated that the application of characterization steps exerts strong adverse effects on the ECSA. This is explained by the “voltage cycling” conditions which are inevitably introduced during the characterization protocols, part of which is conducted under cell voltage as low as 0.2 V.