Failure modes such as carbon deposition must be avoided or controlled in order to ensure the safe operation of auxiliary power units running on diesel reformate or other carbon-containing fuels. Electrochemical impedance spectroscopy (EIS) technology and methodology combined with the distribution of relaxation times (DRT) method could be promising technique to investigate the critical operating conditions or play a role in an online monitoring techniques such as total harmonic distortion analysis (THDA) or fast EIS thus allowing counteractions, for example changing of the operating conditions or cell protecting regeneration. The sample anode-supported solid oxide fuel cells for industrial application are analyzed and characterized with the aim of isolating anode processes and enabling fast detection of carbon depositions. Different process mechanisms are successfully separated using this methodology and without a reference electrode, which is of great importance for the practical usage. This study represents a first step in a broader study which will investigate more into carbon depositions and also other ways of deposition and poisoning of the anode and the cathode. (C) 2016 Elsevier Ltd. All rights reserved.