Multilevel converters use a large amount of semiconductors, allowing the reconfigurate of the converter to work even on internal fault condition. This paper presents a method to detect faulty cells in a cascaded multicell converter requiring just one voltage measurement per output phase. The method is based on high-frequency harmonic analysis, using a dynamic prediction of their behavior, avoiding erroneous detection on transients while keeping the precision under real fault events. Once the faulty cell is detected, it can be bypassed allowing the converter to keep working according to previously reported techniques. Experimental results confirm accurate and fast fault detection, with a good rejection to normal operation transients.